CN114740336B - Amplifier test circuit and test method - Google Patents

Abstract

The invention discloses an amplifier test circuit and a test method, which relate to the field of integrated circuit testing, and comprise a signal source, a multi-channel filter group A, an amplifier to be tested, a multi-channel filter group B, a measuring device and a data processing module, wherein the output end of the signal source is connected to the input end of the multi-channel filter group A, the output end of the multi-channel filter group A is connected to the input end of the amplifier to be tested, the output end of the amplifier to be tested is connected to the input end of the multi-channel filter group B, the output end of the multi-channel filter group B is connected to the input end of the measuring device, and the output end of the measuring device is connected to the input end of the data processing module; the multi-channel filter group A and the multi-channel filter group B each comprise at least two filter paths, and the filter paths can be switched for use; the invention can reduce the accuracy requirements of the amplifier test on the signal source and/or the measuring device, reduce the dependence of the amplifier test on the high-precision signal source and the high-precision measuring device, and has the advantages of high test accuracy, low cost, and the like.

Description

Amplifier test circuit and test method

Technical Field

The present invention relates to the technical field of integrated circuit testing, and in particular to an amplifier testing circuit and a testing method, which are used to reduce the accuracy requirements of amplifier testing on signal sources and measuring devices.

Background technique

Amplifiers are the largest analog integrated circuit modules in the world and are also key components of almost all systems on chips (SoCs). Testing the spectrum performance of low-distortion amplifiers is critical and extremely challenging. To ensure accurate spectrum test results, IEEE standards and industry test techniques require that the total distortion of the signal source and measurement device must be at least ten times or 20 dB lower than that of the circuit under test. Otherwise, the nonlinear errors of the signal source and measurement device will seriously deteriorate the output of the circuit under test. Today, the total harmonic distortion (THD) of commercial low-distortion amplifiers has been as low as -120 dB or even lower. To test the spectrum performance of low-distortion amplifiers, the distortion of the excitation signal provided by the signal source should be at least -140 dB, and the linearity of the test instrument used to collect the output signal of the amplifier under test should be at least 24 bits. The THD value of most current advanced signal generators is only slightly lower than -90 dB. Even after filtering with expensive high-quality bandpass filters, the total harmonic distortion of the resulting signal is only between -120 dB and -130 dB. For measuring devices, taking analog-to-digital converters (ADCs) as an example, high-precision ADCs are usually based on Σ-Δ modulation technology. The conversion rate of such ADCs is so slow that it cannot meet the speed requirements of today's high-precision amplifier spectrum testing. For off-chip test environments, such as mass production testing and characteristic testing, it is very difficult to obtain ultra-low distortion input signals with a total harmonic distortion as low as -140dB and ultra-high-precision measuring devices. For built-in self-test, this requirement is simply impossible to achieve. At present, domestic and foreign academic and industrial circles have conducted a lot of research on the challenges of high-precision signal sources and high-precision measuring devices in amplifier testing, but no practical methods have been reported. Therefore, the problem of low-distortion amplifier spectrum testing needs to be solved urgently.

Summary of the invention

In order to solve the problems existing in the prior art, the present invention provides an amplifier test circuit and a test method, so that a signal source and a measuring device with relatively low precision can be applied to the spectrum test of a low-distortion amplifier.

To achieve the above object, the present invention provides the following technical solution: an amplifier test circuit, comprising a signal source, an amplifier under test, a measuring device and a data processing module, and a multi-channel filter group A connected between the signal source and the amplifier under test and/or a multi-channel filter group B connected between the amplifier under test and the measuring device, wherein the multi-channel filter group A and the multi-channel filter group B each comprise at least two filter paths, and the filter paths can be switched for use;

When the amplifier test circuit only includes the multi-channel filter group A, a low-precision signal source and a high-precision measurement device are used;

When the amplifier test circuit only includes the multi-channel filter group B, a high-precision signal source and a low-precision measurement device are used;

When the amplifier test circuit includes both the multi-channel filter group A and the multi-channel filter group B, a low-precision signal source and a low-precision measurement device are used.

Furthermore, the multi-channel filter group A and the multi-channel filter group B have the same or different circuit structures and both meet the following three requirements: (1) the linearity of the multi-channel filter group is not lower than the linearity of the amplifier under test; (2) the fundamental amplitudes of the signals filtered by different filtering paths of the same filter group are equal; and (3) different filtering paths of the same filter group have different filtering characteristics for signals of the same frequency.

Furthermore, the multi-channel filter group A and the multi-channel filter group B each include a plurality of filters and switches, and the filters meet two conditions: (1) the transfer function of the filter is known; (2) the filter has the function of changing the amplitude and/or phase of the output signal; and the switch is a multiplexer or a plurality of switches, and the linearity of the switch is not lower than the linearity of the amplifier under test.

Furthermore, the signal source is a circuit, instrument or device capable of providing a sinusoidal signal, and the total harmonic distortion of the signal source is at most 80 dB greater than the accuracy requirement specified in the IEEE standard; the measuring device is a circuit, instrument or device having the function of converting an analog signal into a digital signal, and the accuracy of the measuring device is at most 8 bits lower than the accuracy requirement specified in the IEEE standard.

Furthermore, the data processing module is a computer, FPGA or DSP capable of executing algorithms and storing data.

The present invention also provides an amplifier testing method, which tests the above amplifier testing circuit, and the specific steps are as follows:

S1 When the amplifier test circuit has both multi-channel filter group A and multi-channel filter group B, the specific steps are:

S1.1 Multi-channel filter group A includes n filter paths, and multi-channel filter group B includes s filter paths. Select one filter path among the n filter paths of multi-channel filter group A and one filter path among the s filter paths of multi-channel filter group B, connect the two filter paths with a signal source, an amplifier under test, and a measuring device to form an amplifier test circuit, and record the selected filter path;

S1.2 The signal source generates a set of input signals, which are filtered by the multi-channel filter group A and then enter the amplifier under test to stimulate the amplifier under test. The output signal of the amplifier under test is filtered by the multi-channel filter group B, and the measuring device converts the analog signal into a digital signal, which is the test data of this group of filtering paths;

S1.3 changing the filter path in multi-channel filter group A and/or multi-channel filter group B to form another set of amplifier test circuits, and recording the selected filter path;

S1.4 Use a signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, repeat steps S1.2 and S1.3, and collect at least 3 groups and at most n×s groups of test data of different filter paths;

S1.5 data processing module receives the test data output by the measuring device and processes the test data to obtain the spectrum parameters related to the harmonics of the amplifier under test;

S2 When the amplifier test circuit only has the multi-channel filter group A, the specific steps are:

S2.1 The multi-channel filter group A includes n filter paths, one of the n filter paths of the multi-channel filter group A is selected, and the filter path is connected with a signal source, an amplifier under test, and a measuring device to form an amplifier test circuit;

S2.2 The signal source generates a set of input signals, which are filtered by the multi-channel filter group A and then enter the amplifier under test to stimulate the amplifier under test. The output signal of the amplifier under test is converted into a digital signal by the measuring device, which is the test data of the group of filtering paths;

S2.3 changing the filter path of the multi-channel filter group A to form another group of amplifier test circuits, and recording the selected filter path;

S2.4 using a signal source to generate a signal having the same amplitude, frequency and initial phase as the first set of input signals, repeating steps S2.1 and S2.3, and collecting at least two sets of test data of different filter paths;

S3 When the amplifier test circuit has a multi-channel filter group B, the specific steps are:

S3.1 A multi-channel filter group B includes s filter paths, one of the s filter paths in the multi-channel filter group B is selected, and the filter path is connected with a signal source, an amplifier under test, and a measuring device to form an amplifier test circuit;

S3.2 The signal source generates a set of input signals to stimulate the amplifier under test. The output signal of the amplifier under test is filtered by the multi-channel filter group B, and the measuring device converts the analog signal into a digital signal, which is the test data of the group of filter paths;

S3.3 changing the filter path through the multi-path filter group B to form another set of amplifier test circuits, and recording the selected filter path;

S3.4 Use a signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, repeat steps S3.2 and S3.3, and collect test data of at least 2 groups of different filter paths.

Furthermore, in steps S1.3, S2.3 and S3.3, the filtering paths of the multi-channel filter group A and the multi-channel filter group B are changed at least once.

Further, in step S1, when the multi-channel filter group A and the multi-channel filter group B respectively include two filter paths, the harmonic calculation formula of the amplifier under test has four representation forms. Any one of the expression forms can be selected to calculate the harmonic information of the amplifier under test. The four expressions are:

In the formula, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-way filter group A, respectively, and H ₃ and H ₄ are the transfer functions of filter 3 and filter 4 included in the multi-way filter group B, respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and _fin is the frequency of the input signal; h _m1k , h _m2k , h _m3k and h _m4k are the spectrum lines of the kth harmonic of the test data m ₁ , m ₂ , m ₃ and m ₄ , respectively; m ₁ represents the output data collected by the measuring device when filter 1 and filter 3 are selected to be connected into a channel; m ₂ represents the output data collected by the measuring device when filter 1 and filter 4 are selected to be connected into a channel; m ₃ represents the output data collected by the measuring device when filter 2 and filter 3 are selected to be connected into a channel; m ₄ represents the output data collected by the measuring device when filter 2 and filter 4 are selected to be connected into a channel.

Further, in step S2, when the multi-channel filter group A includes two filter paths, the harmonic calculation formula of the amplifier under test has the following two expressions. Any one of the expressions can be selected to calculate the harmonic information of the amplifier under test. The two expressions are respectively:

In the formula, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-path filter group respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and fi _n is the frequency of the input signal; h _m1k and h _m2k are the spectrum lines of the kth harmonic of the test data m ₁ and m ₂ respectively; m ₁ represents the output data collected by the measuring device when filter 1 is selected to be connected into a path; m ₂ represents the output data collected by the measuring device when filter 2 is selected to be connected into a path.

Furthermore, in step S3, when the multi-filter bank B includes two filter paths, the harmonic calculation formula of the amplifier under test has the following expression:

In the formula, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-path filter group respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and fi _n is the frequency of the input signal; h _m1k and h _m2k are the spectrum lines of the kth harmonic of the test data m ₁ and m ₂ respectively; m ₁ represents the output data collected by the measuring device when filter 1 is selected to be connected into a path; m ₂ represents the output data collected by the measuring device when filter 2 is selected to be connected into a path.

Compared with the prior art, the present invention has at least the following beneficial effects:

The amplifier test circuit and test method proposed by the present invention abandon the idea that only high-precision signal sources and high-precision measuring devices with accuracy meeting the IEEE standard accuracy requirements can test the amplifier in the traditional test method, and instead use low-precision signal sources and/or low-precision measuring devices with accuracy lower than the IEEE standard accuracy requirements to test the amplifier under test. Compared with the traditional test method, when two groups of multi-channel filter groups are used, the present invention can simultaneously reduce the accuracy requirements of the signal source and the measuring device, the total harmonic distortion of the signal source can be increased by up to about 60dB, and the accuracy of the measuring device can be reduced by up to about 6 bits; when only one group of multi-channel filter groups is used, the present invention can reduce the accuracy requirements of the signal source or the measuring device separately, and the amplitude of reducing the accuracy requirements is greater, the total harmonic distortion of the signal source can be increased by up to about 80dB, and the accuracy of the measuring device can be reduced by up to about 8 bits. Therefore, the present invention can greatly reduce the test cost of amplifier testing and the dependence on precision instruments.

Since the low-precision signal source and low-precision measuring device used in the present invention both contain nonlinear errors, if the traditional test method is still used to test the amplifier, the nonlinear errors of the signal source and the measuring device will seriously deteriorate the output signal of the amplifier under test, resulting in the inability to obtain the spectrum performance parameters of the amplifier under test. The present invention connects a multi-channel filter group after the signal source and/or the amplifier under test, utilizes the spectrum correlation of the filtered signal, and combines the algorithm provided by the present invention to extract the harmonic information of the amplifier under test from the output signal deteriorated by the signal source and/or the measuring device, and then calculates the spectrum performance parameters of the amplifier under test; since the filter circuit used has a simple structure and is easy to implement, the proposed algorithm has high computational efficiency and accurate parameter estimation, therefore, compared with the traditional method, the present invention only adds a small amount of additional hardware overhead and computing power, and can achieve the purpose of significantly reducing the accuracy requirements of the amplifier test on the signal source and/or the measuring device.

Furthermore, since the present invention has the ability to reduce the accuracy requirements of the signal source and/or the measuring device, the present invention can not only significantly reduce the testing cost, but also solve the problem that the existing test instruments cannot test the ultra-low distortion amplifier, and can also provide a practical solution for built-in self-test and on-chip system testing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a method for testing an amplifier using a low-precision signal source and a low-precision ADC, as proposed by the present invention;

FIG2 is a schematic diagram of a method for testing an amplifier using a low-precision signal source proposed by the present invention;

FIG3 is a schematic diagram of a method for testing an amplifier using a low-precision ADC proposed by the present invention;

4 is a schematic diagram of a circuit using a low-precision signal source and a low-precision ADC test amplifier according to Embodiment 1 of the present invention;

5 is a schematic diagram of a circuit for testing an amplifier using a low-precision signal source according to Embodiment 2 of the present invention;

6 is a schematic diagram of a circuit for testing an amplifier using a low-precision measurement device according to Embodiment 3 of the present invention;

7 is a diagram of simulation results obtained by testing an amplifier with a THD value of -121.42dB using a signal source with a THD value of -79.76dB and a measuring device with a THD value of -118.13dB according to the circuit and method provided in Example 1;

FIG8 is a diagram of simulation results obtained by testing a low-distortion amplifier using a random low-precision signal source and a low-precision measurement device in 500 simulations according to the circuit and method provided in Example 1.

9 is a diagram of simulation results obtained by testing an amplifier with a THD value of -118.08dB using a signal source with a THD value of -67.72dB provided by the circuit and method of Example 2;

FIG10 is a diagram showing simulation results of the circuit and method provided in Example 2, using a measuring device with a 14-bit accuracy to test an amplifier with a THD value of -119.70 dB.

Detailed ways

In order to make the purpose, technical scheme and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, it will be appreciated by those skilled in the art that in the embodiments of the present invention, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical schemes claimed for protection by the claims of the present application can be implemented.

In a first aspect, the present invention provides an amplifier test circuit, as shown in FIG1 , the amplifier test circuit comprises: a signal source, a multi-channel filter group A, an amplifier under test, a multi-channel filter group B, a measuring device and a data processing module, wherein the output end of the signal source is connected to the input end of the multi-channel filter group A, the output end of the multi-channel filter group A is connected to the input end of the amplifier under test, the output end of the amplifier under test is connected to the input end of the multi-channel filter group B, the output end of the multi-channel filter group B is connected to the input end of the measuring device, the output end of the measuring device is connected to the input end of the data processing module, wherein a low-precision signal source and a low-precision measuring device are used.

Preferably, the signal source is used to generate the input signal required for the amplifier test, and the signal source includes but is not limited to a digital-to-analog converter (DAC), a commercial signal source, a function generator, etc.; any circuit, instrument or device that can provide a sinusoidal signal can be regarded as a signal source.

Preferably, the signal source used in the present invention does not need to meet the requirement of at least 3 to 4 bits higher than the accuracy of the circuit under test as stipulated in the IEEE standard. The accuracy of the signal source can be lower than the accuracy requirement of the IEEE standard. Taking the THD value as an example, the THD value of the signal source can be at most about 60dB higher than the accuracy requirement of the IEEE standard.

Preferably, the multi-channel filter group A and the multi-channel filter group B are both composed of a plurality of filters and switches, and are used to filter the output signal of the signal source and the output signal of the amplifier under test respectively, so as to generate a plurality of groups of spectrally related output signals;

The spectral correlation of the output signal means that the filtered output signals can be linked through the transfer function of the filter, so that in the subsequent data processing, the spectral correlation between the output signals can be used to calculate the spectral parameters of the amplifier under test, such as THD, SFDR, etc.

Preferably, the filter must meet the following two conditions: (1) the transfer function of the filter is known; (2) the filter has the function of changing the amplitude or phase of the output signal; the filter includes but is not limited to RC low-pass filters, resistor attenuators, etc. Any circuit that has the function of changing the amplitude, frequency and/or phase characteristics of a signal can be used as a filter;

In particular, the direct path can also be viewed as a filter.

Preferably, the switch is used to change the filtering path of the above-mentioned multi-channel filter group A and multi-channel filter group B. The switch can be a multiplexer or a plurality of switches. The linearity of the switch should not be lower than the linearity of the amplifier under test to avoid introducing additional distortion components.

Preferably, the multi-channel filter group includes at least two channels, and channels may be added according to actual conditions. The multi-channel filter group must meet the following three requirements: (1) The linearity of the multi-channel filter group must be high, and its linearity should not be lower than the linearity of the amplifier under test to avoid introducing additional distortion components; (2) The fundamental amplitudes of signals filtered by different filter channels of the same filter group are equal; (3) Different filter channels of the same filter group have different filtering characteristics for signals of the same frequency.

Preferably, the circuit structure of the multi-channel filter group A and the circuit structure of the multi-channel filter group B may be the same or different;

Measuring devices are used to convert analog signals into digital signals; measuring devices include but are not limited to ADC, spectrum analyzer, etc. Any circuit, instrument or device that has the function of converting analog signals into digital signals can be regarded as a measuring device.

Preferably, the measuring device used in the present invention does not need to meet the requirement of at least 3 to 4 bits higher than the accuracy of the measured circuit as specified in the IEEE standard. The accuracy of the measuring device can be lower than the accuracy requirement of the IEEE standard. Taking resolution as an example, the resolution of the measuring device used in the present invention can be at most about 6 bits lower than the accuracy requirement of the IEEE standard. Preferably, the data processing module is used to obtain dynamic parameter indicators for evaluating the spectral characteristics of the measured amplifier based on multiple groups of output data collected by the measuring device, combined with the transfer function of the known multi-channel filter group, and using the algorithm proposed by the present invention; the data processing module should have the ability to execute algorithms and store data. The data processing module includes but is not limited to computers, FPGAs, DSPs, etc.

To achieve the above-mentioned purpose and other related purposes, in a second aspect, an embodiment of the present invention provides an amplifier testing method, which specifically comprises the following steps:

The first step is to prepare for the test, including: selecting a suitable multi-channel filter group; editing the test program in the data processing module; connecting the signal source, multi-channel filter group A, the amplifier under test, multi-channel filter group B, the measuring device and the data processing module;

The second step is to select a filter path in the multi-channel filter group A and a filter path in the multi-channel filter group B, connect the two filter paths with the signal source, the amplifier under test and the measuring device to form a set of test paths, and record the selected filters;

In the third step, the signal source generates a set of input signals, which are filtered by the multi-channel filter group A and then enter the amplifier under test to stimulate the amplifier under test. The output signal of the amplifier under test is filtered by the multi-channel filter group B, and the measuring device converts the analog signal into a digital signal to obtain the test data of the group of filter paths.

Step 4: The data processing module receives and stores the test data collected by the measuring device;

Step 5: changing the filter paths in the multi-channel filter group A and/or the multi-channel filter group B to form another set of test paths, and recording the selected filters;

The sixth step is to use a signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, and repeat the third step, the fourth step and the fifth step until a sufficient number of test data of different filter paths are collected; the number of test data groups is determined by the number of filters included in the multi-channel filter group A and the multi-channel filter group B. For example, the multi-channel filter group A contains n (n≥2) filter paths, and the multi-channel filter group B contains s (s≥2) filter paths. Then the number of test data groups required is at least 3 groups and at most n×s groups, wherein the filter path of the multi-channel filter group A is changed at least once, and the filter path of the multi-channel filter group B is changed at least once.

Step 7: In the data processing module, the collected data is processed. When the multi-channel filter group A and the multi-channel filter group B each contain two filter paths, there are four representations of the harmonic calculation formula of the amplifier under test. Any one of the representations can be used to calculate the harmonic information of the amplifier under test. The four calculation formulas are:

Wherein, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-channel filter group A, respectively, and H ₃ and H ₄ are the transfer functions of filter 3 and filter 4 included in the multi-channel filter group B, respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and fi _n is the frequency of the input signal; h _m1k , h _m2k , h _m3k and h _m4k are the spectrum lines of the kth harmonic of the test data m ₁ , m ₂ , m ₃ and m ₄ , respectively; m ₁ represents the output data collected by the measuring device when filter 1 and filter 3 are selected to be connected into a channel; m ₂ represents the output data collected by the measuring device when filter 1 and filter 4 are selected to be connected into a channel; m ₃ represents the output data collected by the measuring device when filter 2 and filter 3 are selected to be connected into a channel; m ₄ represents the output data collected by the measuring device when filter 2 and filter 4 are selected to be connected into a channel;

The calculation formulas for the total harmonic distortion THD and spurious-free dynamic range SFDR of the amplifier under test are:

THD＝10log ₁₀ (∑ _k≥2 |2h _uk | ² ) (5)

As shown in FIG2 , when only the accuracy requirement of the signal source for the amplifier test is reduced, a multi-channel filter group A can be set only between the signal source and the amplifier under test, and the amplifier can be tested using a low-precision signal source and a high-precision measurement device. Specifically:

1. The present invention uses a high-precision measuring device that meets the accuracy requirements of the IEEE standard to test the amplifier, that is, the distortion of the measuring device is at least ten times or 20 dB lower than the distortion of the amplifier under test, so as to avoid the nonlinear distortion of the measuring device from deteriorating the output of the amplifier under test.

2. The present invention can further reduce the accuracy requirements of the amplifier test on the signal source. Compared with the accuracy requirements of the IEEE standard, the present invention can reduce the accuracy requirements of the amplifier test on the signal source by up to about 80dB;

3. The test steps of the amplifier test circuit are as follows:

3.1 The multi-channel filter group A includes n filter paths, one of the n filter paths of the multi-channel filter group A is selected, and the filter path is connected with a signal source, an amplifier under test and a measuring device to form an amplifier test circuit;

3.2 The signal source generates a set of input signals, which are filtered by the multi-channel filter group A and then stimulate the amplifier under test. The output signal of the amplifier under test is converted into a digital signal by the measuring device, which is the test data of the group of filtering paths;

3.3 Change the filter path of the multi-channel filter group A to form another set of amplifier test circuits, and record the selected filter path;

3.4 Use a signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, repeat steps 3.2 and 3.3, change the filtering path of multi-channel filter group A at least once, and collect test data of at least 2 groups of different filtering paths.

4. When the multi-channel filter group A contains two filter paths and the collected test data is 2 groups, the method is used to calculate the harmonic calculation formula of the amplifier under test in the following two forms, and any one of them can calculate the harmonic information of the amplifier under test. The two calculation formulas are:

Wherein, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-channel filter group A respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and _fin is the frequency of the input signal; h _m1k and h _m2k are the spectrum lines of the kth harmonic of the test data m ₁ and m ₂ respectively; m ₁ represents the output data collected by the measuring device when filter 1 is selected to be connected as a path; m ₂ represents the output data collected by the measuring device when filter 2 is selected to be connected as a path;

As shown in FIG3 , when only the accuracy requirement of the amplifier test on the measuring device is reduced, a multi-channel filter group B can be set only between the amplifier under test and the measuring device, and a high-precision signal source and a low-precision measuring device can be used. Specifically:

1. The present invention uses a high-precision signal source that meets the IEEE standard accuracy requirements to test the amplifier, that is, the distortion of the signal source is at least ten times or 20 dB lower than the distortion of the amplifier under test, so as to avoid the nonlinear distortion of the signal source from deteriorating the output of the amplifier under test.

2. The present invention can further reduce the accuracy requirements of amplifier testing on measuring devices. Compared with the accuracy requirements of the IEEE standard, the present invention can reduce the accuracy requirements of amplifier testing on measuring devices by up to about 8 bits;

3. The test steps of the amplifier test circuit are as follows:

3.1 The multi-channel filter group B includes s filter paths, one of the s filter paths in the multi-channel filter group B is selected, and the filter path is connected with a signal source, an amplifier under test and a measuring device to form an amplifier test circuit;

3.2 The signal source generates a set of input signals, which enter the amplifier under test to stimulate the amplifier under test. The output signal of the amplifier under test is filtered by the multi-channel filter group B, and the measuring device converts the analog signal into a digital signal, which is the test data of the group of filtering paths;

3.3 Change the filter path through the multi-channel filter group B to form another set of amplifier test circuits, and record the selected filter path;

3.4 Use a signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, repeat steps 3.2 and 3.3, change the filtering path of multi-channel filter group B at least once, and collect test data of at least 2 groups of different filtering paths.

4. When the multi-channel filter group B contains two filter paths and the collected test data is 2 groups, the harmonic calculation formula used by this method to calculate the amplifier under test has the following expression:

In the formula, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-path filter group B respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and fi _n is the frequency of the input signal; h _m1k and h _m2k are the spectrum lines of the kth harmonic of the test data m ₁ and m ₂ respectively; m ₁ represents the output data collected by the measuring device when filter 1 is selected to be connected into a path; m ₂ represents the output data collected by the measuring device when filter 2 is selected to be connected into a path.

Example 1

An amplifier test circuit and test method provided by the present invention are used to reduce the accuracy requirements of the amplifier test on the signal source and the measurement device, as shown in FIG4 , and specifically include the following steps:

First, in this embodiment, the multi-channel filter group A and the multi-channel filter group B have the same circuit structure; the multi-channel filter group A is composed of filter 1 and filter 2 connected in parallel, and the multi-channel filter group B is composed of filter 3 and filter 4 connected in parallel; filter 1 and filter 3 are first-order low-pass RC filters, and their transfer functions can be expressed as follows:

Where ω ₀ is the corner frequency of filter 1, _RL and _CL are the resistance and capacitance that constitute the first-order low-pass RC filter.

Filter 2 and filter 4 are resistor attenuators, and their transfer functions can be expressed as

Where _R1 and _R2 are the resistors that make up the resistance attenuator.

The second step is to select a suitable signal source and measurement device. For example, a signal source with a THD value about 60 dB higher than the IEEE standard accuracy requirement and an ADC with an accuracy about 4 bits lower than the IEEE standard accuracy requirement.

The third step is to connect the circuit and make preparations before the test, including: editing the test program in the data processing module; connecting the signal source, multi-channel filter group A, the amplifier under test, multi-channel filter group B, the measuring device and the data processing module;

Step 4, select the filter 1 path of the multi-channel filter group A and the filter 3 path of the multi-channel filter group B, connect the filter 1 path and the filter 3 path with the above-mentioned signal source, the amplifier under test and the measuring device to form a first group of test paths, and record the selected filter paths;

Step 5: The signal source generates a set of input signals, which are filtered by the multi-channel filter group A. The filtered input signals excite the amplifier under test. The output signals of the amplifier under test are filtered by the multi-channel filter group B and then input into the measuring device. The measuring device converts the analog signals into digital signals and transmits them to the data processing module.

Step 6: The data processing module receives the digital signal output by the measuring device and stores the group of data as m ₁ ;

Step 7: Change the selection of filter paths in the multi-channel filter group A and the multi-channel filter group B through the switch, select the filter 1 path of the multi-channel filter group A and the filter 4 path of the multi-channel filter group B, connect the filter 1 path and the filter 4 path with the signal source, the amplifier under test and the measuring device to form a second group of test paths, record the selected filter, use the signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, repeat the fifth and sixth steps, and record the reorganized data as m ₂ ;

Step 8: Change the selection of filter paths in the multi-channel filter group A and the multi-channel filter group B by using switches, select the filter 2 path of the multi-channel filter group A and the filter 3 path in the multi-channel filter group B, connect the filter 2 path, the filter 3 path, the signal source, the amplifier under test and the measuring device to form a third group of test paths, record the selected filter, use the signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, repeat the fifth and sixth steps, and record the reorganized data as m ₃ ;

The ninth step is to process the collected data (m ₁ , m ₂ and m ₃ ) in the data processing module; the harmonic calculation formula of the amplifier under test is expressed as:

Wherein, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-channel filter group A, respectively, and H ₃ and H ₄ are the transfer functions of filter 3 and filter 4 included in the multi-channel filter group B, respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and _fin is the frequency of the input signal; h _m1k , h _m2k and h _m3k are the spectrum lines of the kth harmonic of the test data m ₁ , m ₂ and m ₃ , respectively; m ₁ represents the output data collected by the measuring device when filter 1 and filter 3 are selected to be connected into a channel; m ₂ represents the output data collected by the measuring device when filter 1 and filter 4 are selected to be connected into a channel; m ₃ represents the output data collected by the measuring device when filter 2 and filter 3 are selected to be connected into a channel;

The calculation formulas for the total harmonic distortion THD and spurious-free dynamic range SFDR of the amplifier under test are:

THD＝10log ₁₀ (∑ _k≥2 |2h _uk | ² ) (5)

FIG7 is a diagram of simulation results obtained by testing an amplifier with a THD value of -121.42dB using a signal source with a THD value of -79.76dB and a measuring device with a THD value of -118.13dB according to the circuit and method provided by the present invention. In the figure, the x-axis represents the normalized frequency, the y-axis represents the normalized power, the spectrum marked with an asterisk represents the real spectrum diagram of the amplifier under test, and the spectrum marked with a circle represents the simulated spectrum diagram obtained by the method of the present invention. In order to accurately test the spectrum performance of an amplifier with a THD value of -121.42dB, the traditional method requires the THD value of the signal source and the measuring device to be as low as -140dB, which not only requires expensive testing instruments, but is almost impossible to achieve on-chip testing. The method provided by the present invention only uses a signal source with a THD value of -79.76dB and a measuring device with a THD value of -118.13dB to test an amplifier with a THD value of -121.42dB, and the test accuracy of the method of the present invention is the same as that of the traditional method. Compared with traditional methods, the method of the present invention can reduce the accuracy requirements of the amplifier test on the signal source by about 60dB and the accuracy requirements of the amplifier test on the measuring device by about 20dB while obtaining accurate test results, significantly reducing the demand for precision test instruments and thus greatly reducing test costs.

FIG8 is a diagram of simulation results obtained by randomly using low-precision signal sources and low-precision measuring devices to test a low-distortion amplifier in 500 simulations according to the circuit and method provided by the present invention. In the simulation, the total harmonic distortion of the amplifier is randomly generated in the range of -125dB to -115dB. In the figure, the x-axis represents the THD value of the amplifier under test, the y-axis represents the THD error value of the amplifier under test obtained by the present invention, and the asterisk mark represents a single simulation result. As can be seen from the figure, the THD value of the amplifier measured by the method of the present invention has a small error with its true value, and the maximum error is only 0.97dB.

Example 2

An amplifier test circuit and a test method provided by the present invention are used to reduce the accuracy requirement of the amplifier test on the signal source, as shown in FIG5 , and specifically include the following steps:

In the first step, in this embodiment, the multi-channel filter group A is composed of filter 1 and filter 2 connected in parallel. Filter 1 is a second-order low-pass RC filter, and its transfer function can be expressed as:

Where _ωn is the natural angular frequency, ζ is the damping coefficient, _RL1 , _RL2 , _CL1 and _CL2 are respectively the resistor and capacitor constituting a second-order low-pass RC filter.

Filter 2 is a resistor attenuator, and its transfer function can be expressed as:

Where _R1 and _R2 are the resistors that make up the resistance attenuator.

The second step is to select a suitable signal source and measurement device. For example, select a signal source with a THD value about 70dB higher than the IEEE standard accuracy requirement, and select an ADC with an accuracy that meets the IEEE standard accuracy requirement.

The third step is to connect the circuit and make preparations before testing, including: editing the test program in the data processing module; connecting the signal source, the multi-channel filter group A, the amplifier under test, the measuring device and the data processing module;

Step 4, select the filter 1 path of the multi-path filter group A, connect the above signal source, the amplifier under test and the measuring device into the first group of test paths, and record the selected filter path;

Step 5: The signal source generates a set of input signals, which are filtered by the multi-channel filter group A. The filtered input signals excite the amplifier under test, and the output signals of the amplifier under test are input into the measuring device. The measuring device converts the analog signals into digital signals and transmits them to the data processing module.

Step 6: The data processing module receives the digital signal output by the measuring device and stores the group of data as m ₁ ;

Step 7: Change the filter path of the multi-channel filter group A through the switch, select the filter 2 path of the multi-channel filter group A, connect it with the signal source, the amplifier under test and the measuring device to form the second test path, record the selected filter, use the signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, and repeat the fifth and sixth steps, and record the reorganized data as m ₂ ;

Step 8: In the data processing module, the collected data ( _m1 and _m2 ) are processed; the harmonic calculation formula of the amplifier under test has two representation forms. Either expression form can be used to calculate the harmonic spectrum of the amplifier under test. The two calculation formulas are:

Wherein, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-channel filter group A respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and _fin is the frequency of the input signal; h _m1k and h _m2k are the spectrum lines of the kth harmonic of the test data m ₁ and m ₂ respectively; m ₁ represents the output data collected by the measuring device when filter 1 is selected to be connected as a path; m ₂ represents the output data collected by the measuring device when filter 2 is selected to be connected as a path;

The calculation formulas for the total harmonic distortion THD and spurious-free dynamic range SFDR of the amplifier under test are:

THD＝10log ₁₀ (∑ _k≥2 |2h _uk | ² ) (5)

FIG9 is a diagram of simulation results obtained by testing an amplifier with a THD value of -118.08dB using a signal source with a THD value of -67.72dB according to the circuit and method provided by the present invention. In the figure, the x-axis represents the normalized frequency, the y-axis represents the normalized power, the spectrum marked with an asterisk represents the real spectrum diagram of the amplifier under test, and the spectrum marked with a circle represents the simulated spectrum diagram obtained according to the method of the present invention. In order to test the spectrum characteristics of an amplifier with a THD value of -118.08dB, the traditional method requires the THD value of the signal source to be as low as about -140dB. For existing high-precision signal sources, it is almost impossible to generate such a low-distortion signal. The method provided by the present invention only uses a signal source with a THD value of -67.72dB to test an amplifier with a THD value of -118.08dB, and the test accuracy of the method of the present invention is the same as that of the traditional method. Compared with the traditional method, the method of the present invention can reduce the accuracy requirement of the amplifier test on the signal source by about 70dB under the condition of obtaining accurate test results, significantly reducing the demand for precision instruments in the amplifier test, thereby greatly reducing the test cost.

Example 3

When an amplifier test circuit provided by the present invention is used to test an amplifier, as shown in FIG6 , the following steps are specifically included:

In the first step, in this embodiment, the multi-channel filter group B is composed of filter 1 and filter 2 connected in parallel, and filter 1 is an active first-order low-pass RC filter, and its transfer function can be expressed as:

Where ω ₀ is the corner frequency of filter 1, _RL1 , _RL2 , _RL3 and _CL are the resistor and capacitor respectively constituting an active first-order low-pass RC filter.

Filter 2 is a direct path, and its transfer function can be expressed as

_H2 (jω)＝1

The second step is to select a suitable signal source and measurement device. For example, select a signal source whose THD value meets the accuracy requirements of the IEEE standard, and select an ADC whose accuracy is about 8 bits lower than the accuracy requirements of the IEEE standard.

The third step is to connect the circuit and make preparations before testing, including: editing the test program in the data processing module; connecting the signal source, the amplifier under test, the multi-channel filter group B, the measuring device and the data processing module;

Step 4, select the filter 1 path of the multi-path filter group B, connect the above signal source, the amplifier under test and the measuring device into the first group of test paths, and record the selected filter path;

Step 5: The signal source generates a set of input signals to excite the amplifier under test. The output signal of the amplifier under test is filtered by the multi-channel filter group B. The filtered input signal is input into the measuring device. The measuring device converts the analog signal into a digital signal and transmits it to the data processing module.

Step 6: The data processing module receives the digital signal output by the measuring device and stores the group of data as m ₁ ;

Step 7: Change the filter path of the multi-channel filter group through the switch, select the filter 2 path of the multi-channel filter group B, connect it with the signal source, the amplifier under test and the measuring device to form the second test path, record the selected filter, use the signal source to generate a signal with the same amplitude, frequency and initial phase as the first group of input signals, and repeat the fifth and sixth steps, and record the reorganized data as m ₂ ;

Step 8: In the data processing module, the collected data (m ₁ and m ₂ ) are processed; the harmonic calculation formula of the amplifier under test has the following expression:

In the formula, h _uk is the spectrum line of the kth harmonic of the amplifier under test; H ₁ and H ₂ are the transfer functions of filter 1 and filter 2 included in the multi-path filter group B respectively; ω is the corner frequency of the filter, ω=2×π× _fin , and fi _n is the frequency of the input signal; h _m1k and h _m2k are the spectrum lines of the kth harmonic of the test data m ₁ and m ₂ respectively; m ₁ represents the output data collected by the measuring device when filter 1 is selected to be connected into a path; m ₂ represents the output data collected by the measuring device when filter 2 is selected to be connected into a path.

The calculation formulas for the total harmonic distortion THD and spurious-free dynamic range SFDR of the amplifier under test are:

THD＝10log ₁₀ (∑ _k≥2 |2h _uk | ² ) (5)

FIG10 is a simulation result diagram obtained by testing an amplifier with a THD value of -119.70dB using a measuring device with a precision of 14 bits according to the circuit and method provided by the present invention. In the figure, the x-axis represents the normalized frequency, the y-axis represents the normalized power, the spectrum marked with an asterisk represents the real spectrum diagram of the amplifier under test, and the spectrum marked with a circle represents the simulated spectrum diagram obtained according to the method of the present invention. In order to accurately test the spectrum performance of an amplifier with a THD value of -119.70dB, the traditional method requires the accuracy of the measuring device to be at least 22 bits, and for existing measuring devices, it is usually faced with a compromise between accuracy and speed, bandwidth, etc. The method provided by the present invention can test an amplifier with a THD value of -119.70dB using only a 14-bit measuring device, and the test accuracy of the method of the present invention is the same as that of the traditional method. Compared with the traditional method, the method of the present invention can reduce the accuracy requirement of the measuring device for amplifier testing by about 8 bits under the condition of obtaining accurate test results, significantly reducing the demand for precision testing instruments for amplifier testing, thereby greatly reducing the test cost.

Therefore, the present invention can significantly reduce the accuracy requirements of the amplifier test on the signal source and/or measurement device, thereby greatly reducing the test cost of the amplifier test, solving the problem of the difficulty in obtaining high-precision test instruments in ultra-low distortion amplifier testing, and providing a practical solution for on-chip testing of amplifiers.

Claims (8)

1. The amplifier testing method is characterized in that an amplifier testing circuit comprises a signal source, a tested amplifier, a measuring device and a data processing module, and a multipath filter bank A connected between the signal source and the tested amplifier and/or a multipath filter bank B connected between the tested amplifier and the measuring device, wherein the multipath filter bank A and the multipath filter bank B at least comprise two filter paths, and the filter paths can be switched for use;

when the amplifier test circuit only comprises a multipath filter group A, a low-precision signal source and a high-precision measuring device are adopted;

when the amplifier test circuit only comprises a multipath filter bank B, a high-precision signal source and a low-precision measuring device are adopted;

when the amplifier test circuit comprises a multipath filter group A and a multipath filter group B, a low-precision signal source and a low-precision measuring device are adopted;

The specific steps for testing by adopting the amplifier testing circuit are as follows:

s1, when the amplifier test circuit is provided with a multipath filter group A and a multipath filter group B, the specific steps are as follows:

S1.1, a multipath filter bank A comprises n filter paths, a multipath filter bank B comprises S filter paths, one filter path of the n filter paths of the multipath filter bank A and one filter path of the S filter paths of the multipath filter bank B are selected, the two filter paths, a signal source, a tested amplifier and a measuring device are connected into a group of amplifier test circuits, and the selected filter paths are recorded;

S1.2, the signal source generates a group of input signals, the input signals are filtered by a multipath filter bank A, the tested amplifier is excited, the output signals of the tested amplifier are filtered by a multipath filter bank B, and the analog signals are converted into digital signals by the measuring device, namely the test data of the group of filter paths;

s1.3, changing filter paths in a multi-path filter group A and/or a multi-path filter group B to form another set of amplifier test circuits, and recording the selected filter paths;

S1.4, generating signals with the same amplitude, frequency and initial phase as the first group of input signals by using a signal source, repeating the steps S1.2 and S1.3, and collecting test data of at least 3 groups and at most n multiplied by S groups of different filter paths;

s1.5, the data processing module receives test data output by the measuring device and processes the test data to obtain frequency spectrum parameters related to harmonic waves of the amplifier to be measured;

s2, when the amplifier test circuit is only provided with the multipath filter group A, the specific steps are as follows:

S2.1, the multipath filter bank A comprises n filter paths, one filter path of the n filter paths of the multipath filter bank A is selected, and the filter paths, a signal source, a tested amplifier and a measuring device are connected into a group of amplifier test circuits;

s2.2, the signal source generates a group of input signals, the input signals are filtered by the multipath filter bank A and then enter the tested amplifier to excite the tested amplifier, and the output signals of the tested amplifier are converted into digital signals by the measuring device, namely the test data of the group of filter paths;

S2.3, changing the filter paths of the multipath filter bank A to form another set of amplifier test circuits, and recording the selected filter paths;

S2.4, generating signals with the same amplitude, frequency and initial phase as the first group of input signals by using a signal source, repeating the steps S2.1 and S2.3, and collecting test data of at least 2 groups of different filter paths;

S3, when the amplifier test circuit is provided with the multipath filter group B, the specific steps are as follows:

S3.1, the multipath filter bank B comprises S filter paths, one filter path of the S filter paths in the multipath filter bank B is selected, and the filter paths, a signal source, a tested amplifier and a measuring device are connected into a group of amplifier test circuits;

S3.2, the signal source generates a group of input signals to excite the tested amplifier, the output signals of the tested amplifier are filtered by the multipath filter bank B, and the analog signals are converted into digital signals by the measuring device, namely the test data of the group of filter paths;

s3.3, changing the filter path passing through the multipath filter bank B to form another set of amplifier test circuits, and recording the selected filter path;

S3.4, generating signals with the same amplitude, frequency and initial phase as the first group of input signals by using a signal source, repeating the steps S3.2 and S3.3, and collecting test data of at least 2 groups of different filter paths;

in step S1, when the multipath filter bank a and the multipath filter bank B respectively include two filter paths, the harmonic calculation formula of the tested amplifier has four expression forms, one expression form is arbitrarily selected, the harmonic information of the tested amplifier can be calculated, and the four expression forms are respectively:

Wherein h _uk is the spectral line of the kth harmonic of the amplifier to be tested; h ₁ and H ₂ are transfer functions of the filter 1 and the filter 2 included in the multiple filter bank a, respectively, and H ₃ and H ₄ are transfer functions of the filter 3 and the filter 4 included in the multiple filter bank B, respectively; ω is the turning frequency of the filter, ω=2×pi×f _in,f_in is the frequency of the input signal; h _m1k、h_m2k、h_m3k and h _m4k are the spectral lines of the kth harmonic of the test data m ₁、m₂、m₃ and m ₄, respectively; m ₁ represents output data collected by the measuring device when the filter 1 and the filter 3 are selected to be connected in a path; m ₂ represents output data collected by the measuring device when the filter 1 and the filter 4 are selected to be connected in a path; m ₃ represents output data collected by the measuring device when the filter 2 and the filter 3 are selected to be connected in a path; m ₄ denotes output data collected by the measuring device when the filter 2 and the filter 4 are selected to be connected in a path.

2. The method for testing an amplifier according to claim 1, wherein the multiple filter bank a and the multiple filter bank B have the same or different circuit structures, and each of the three following requirements is satisfied: (1) The linearity of the multipath filter bank is not lower than that of the amplifier to be tested; (2) The fundamental wave amplitude values of the signals filtered by different filtering paths of the same group of filter banks are equal; (3) Different filter paths of the same set of filter banks have different filter characteristics for signals of the same frequency.

3. The amplifier testing method according to claim 1, wherein the multipath filter bank a and the multipath filter bank B each comprise a plurality of filters and switches, and the filters satisfy two conditions: (1) the transfer function of the filter is known; (2) The filter has the function of changing the amplitude and/or phase of the output signal; the switch is a multiplexer or a plurality of switches, and the linearity of the switch is not lower than that of the amplifier to be tested.

4. An amplifier testing method according to claim 1, wherein the signal source is a circuit, instrument or device capable of providing a sinusoidal signal, the total harmonic distortion of the signal source being at most 80dB greater than the accuracy requirements specified by the IEEE standard; the measuring device is a circuit, instrument or device having the function of converting an analog signal into a digital signal, the accuracy of the measuring device being at most 8 bits lower than the accuracy requirements specified by the IEEE standard.

5. The method of claim 1, wherein the data processing module is a computer, FPGA or DSP capable of executing an algorithm and storing data.

6. The method according to claim 1, wherein in steps S1.3, S2.3 and S3.3, the filter paths of the multiple filter bank a and the multiple filter bank B are changed at least 1 time.

7. The method of claim 1, wherein in step S2, when the multipath filter bank a includes two filter paths, the harmonic calculation formula of the tested amplifier has the following two expression forms, and one expression form is arbitrarily selected, and the harmonic information of the tested amplifier can be calculated, where the two expression forms are respectively:

Wherein h _uk is the spectral line of the kth harmonic of the tested amplifier; h ₁ and H ₂ are transfer functions of the filter 1 and the filter 2 included in the multipath filter bank, respectively; ω is the turning frequency of the filter, ω=2×pi×f _in,f_in is the frequency of the input signal; h _m1k and h _m2k are the spectral lines of the kth harmonic of the test data m ₁ and m ₂, respectively; m ₁ represents output data collected by the measuring device when the selection filter 1 is connected as a path; m ₂ denotes output data collected by the measuring device when the selection filter 2 is connected in the path.

8. The method according to claim 1, wherein in step S3, when the multi-filter bank B includes two filter paths, the harmonic calculation formula of the tested amplifier has the following expression:

Wherein h _uk is the spectral line of the kth harmonic of the tested amplifier; h ₁ and H ₂ are transfer functions of the filter 1 and the filter 2 included in the multipath filter bank, respectively; ω is the turning frequency of the filter, ω=2×pi×f _in,f_in is the frequency of the input signal; h _m1k and h _m2k are the spectral lines of the kth harmonic of the test data m ₁ and m ₂, respectively; m ₁ represents output data collected by the measuring device when the selection filter 1 is connected as a path; m ₂ denotes output data collected by the measuring device when the selection filter 2 is connected in the path.