CN114740336B - Amplifier test circuit and test method - Google Patents
Amplifier test circuit and test method Download PDFInfo
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- CN114740336B CN114740336B CN202210529007.7A CN202210529007A CN114740336B CN 114740336 B CN114740336 B CN 114740336B CN 202210529007 A CN202210529007 A CN 202210529007A CN 114740336 B CN114740336 B CN 114740336B
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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Abstract
The invention discloses an amplifier test circuit and a test method, which relate to the field of integrated circuit test and comprise a signal source, a multipath filter group A, a tested amplifier, a multipath filter group B, a measuring device and a data processing module, wherein the output end of the signal source is connected with the input end of the multipath filter group A; 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; the invention can reduce the precision requirement 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 precision, low cost and the like.
Description
Technical Field
The invention relates to the technical field of integrated circuit testing, in particular to an amplifier testing circuit and an amplifier testing method, which are used for reducing the precision requirements of amplifier testing on a signal source and a measuring device.
Background
Amplifiers are the largest volume analog integrated circuit modules in the world and are also a key component of almost all systems on chip (SoCs). Spectral performance testing of low distortion amplifiers is critical and very challenging. To ensure accurate spectral 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 20dB less than that of the circuit under test, otherwise, nonlinear errors of the signal source and measurement device will severely degrade the output of the circuit under test. Today, the total harmonic distortion (total harmonic distortion, THD) of commercial low distortion amplifiers is already as low as-120 dB, or even lower. To test the spectral performance of a low distortion amplifier, the signal source should provide an excitation signal with a distortion of at least-140 dB, and the test instrument collecting the output signal of the amplifier under test should have a linearity of at least 24 bits. The THD value of most of the current advanced-performance signal generators is only slightly lower than-90 dB, and the total harmonic distortion of the obtained signals is only between-120 dB and-130 dB even after the signals are filtered by adopting an expensive high-quality band-pass filter. For measurement devices, taking analog-to-digital converter (ADC) as an example, high-precision ADCs are typically based on sigma-delta modulation techniques, the conversion rate of such ADCs is too slow to meet the speed requirements of today's high-precision amplifier spectrum testing. For off-chip test environments, such as mass production tests, property tests, etc., it is very difficult to obtain ultra-low distortion input signals with total harmonic distortion as low as-140 dB and ultra-high precision measurement devices. For built-in self-tests, this requirement cannot be fulfilled at all. At present, the academic circles and the industry at home and abroad have conducted a great deal of research on the aspect of coping with challenges of high-precision signal sources and high-precision measuring devices in amplifier tests, and no practical method has been reported yet. Therefore, the problem of low distortion amplifier spectrum testing needs to be solved.
Disclosure of Invention
In order to solve the problems in the prior art, the 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.
In order to achieve the above purpose, the present invention provides the following technical solutions: the amplifier test 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 multiplexing filter set A and a multiplexing filter set B, a low-precision signal source and a low-precision measuring device are adopted.
Furthermore, the multipath filter group A and the multipath filter group B have the same or different circuit structures, and all the following three requirements are met: (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.
Further, 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.
Further, 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 80dB greater than the precision requirement 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.
Further, the data processing module is a computer, an FPGA or a DSP with the capability of executing an algorithm and storing data.
The invention also provides an amplifier testing method, which tests the amplifier testing circuit, and comprises the following specific steps:
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 and then enter a tested amplifier to excite the tested amplifier, the output signals of the tested amplifier are filtered by a multipath filter bank B, and then the analog signals are converted into digital signals by a 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, signals with the same amplitude, frequency and initial phase as the first group of input signals are generated by using a signal source, the steps S3.2 and S3.3 are repeated, and test data of at least 2 groups of different filter paths are acquired.
Further, in steps S1.3, S2.3 and S3.3, the filtering paths of the multiple filter bank a and the multiple filter bank B are changed at least 1 time.
Further, 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, and the harmonic information of the tested amplifier can be calculated, where 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,fin is the frequency of the input signal; h m1k、hm2k、hm3k 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.
Further, 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, so that 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,fin 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.
Further, in step S3, when the multi-filter bank B includes two filter paths, the harmonic calculation formula of the amplifier to be tested 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,fin 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.
Compared with the prior art, the invention has at least the following beneficial effects:
The invention provides an amplifier test circuit and a test method, which abandon the idea that in the traditional test method, only a high-precision signal source and a high-precision measuring device with precision meeting the IEEE standard precision requirement can be used for testing an amplifier, and instead, a low-precision signal source and/or a low-precision measuring device with precision lower than the IEEE standard precision requirement are used for testing the tested amplifier; when only one group of multipath filter banks is used, the invention can independently reduce the accuracy requirement of a signal source or a measuring device, the amplitude of the accuracy requirement is reduced to be larger, the total harmonic distortion of the signal source can be improved by at most about 80dB, and the accuracy of the measuring device can be reduced by at most about 8 bits. Therefore, the invention can greatly reduce the test cost of amplifier test and the dependence on precise instruments.
Because the low-precision signal source and the low-precision measuring device adopted by the invention both contain nonlinear errors, if the amplifier is still tested by adopting the traditional testing method, the nonlinear errors of the signal source and the measuring device can seriously deteriorate the output signal of the tested amplifier, so that the spectral performance parameters of the tested amplifier cannot be obtained. According to the invention, the multipath filter bank is connected behind the signal source and/or the tested amplifier, and the harmonic information of the tested amplifier can be extracted from the output signal deteriorated by the signal source and/or the measuring device by utilizing the spectrum correlation of the filtered signal and combining the algorithm provided by the invention, so that the spectrum performance parameter of the tested amplifier can be calculated; because the filter circuit has simple structure and easy realization, the proposed algorithm has high operation efficiency and accurate parameter estimation, compared with the traditional method, the invention can achieve the aim of greatly reducing the accuracy requirement of the amplifier test on the signal source and/or the measuring device by only adding a small amount of hardware expenditure and calculation force.
Furthermore, the invention has the capability of reducing the precision requirement of a signal source and/or a measuring device, so that the invention not only can obviously reduce the test cost, but also can solve the problem that the existing test instrument cannot test the ultralow distortion amplifier, and can provide a practical solution for built-in self-test and system-on-chip test.
Drawings
FIG. 1 is a schematic diagram of a method of testing an amplifier using a low-precision signal source and a low-precision ADC according to the present invention;
FIG. 2 is a schematic diagram of a method of testing an amplifier using a low precision signal source according to the present invention;
FIG. 3 is a schematic diagram of a method of testing an amplifier using a low-precision ADC according to the present invention;
FIG. 4 is a schematic circuit diagram of a test amplifier employing a low precision signal source and a low precision ADC according to embodiment 1 of the present invention;
FIG. 5 is a schematic circuit diagram of a test amplifier employing a low precision signal source in accordance with embodiment 2 of the present invention;
FIG. 6 is a schematic circuit diagram of a test amplifier employing a low precision measurement device according to embodiment 3 of the present invention;
FIG. 7 is a graph of simulation results from testing an amplifier having a THD value of-121.42 dB using a signal source having a THD value of-79.76 dB and a measurement device having a THD value of-118.13 dB in accordance with the circuit and method provided in example 1;
Fig. 8 is a graph of simulation results of testing a low distortion amplifier using a low precision signal source and a low precision measurement device randomly in 500 simulations according to the circuit and method provided in example 1.
FIG. 9 is a graph of simulation results of the circuit and method provided in example 2 using a signal source with a THD value of-67.72 dB to test an amplifier with a THD value of-118.08 dB;
fig. 10 is a graph of simulation results of testing an amplifier having a THD value of-119.70 dB using a 14-bit measurement device, using the circuit and method provided in example 2.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art will understand that in the embodiments of the present application, numerous technical details have been set forth in order to provide a better understanding of the present application. The technical solutions claimed in the claims of the present application can be realized without these technical details and various changes and modifications based on the following embodiments.
In a first aspect, the present invention provides an amplifier test circuit, as shown in fig. 1, comprising: the device comprises a signal source, a multipath filter group A, a tested amplifier, a multipath filter group B, a measuring device and a data processing module, wherein the output end of the signal source is connected with the input end of the multipath filter group A, the output end of the multipath filter group A is connected with the input end of the tested amplifier, the output end of the tested amplifier is connected with the input end of the multipath filter group B, the output end of the multipath filter group B is connected with the input end of the measuring device, and the output end of the measuring device is connected with the input end of the data processing module, wherein a low-precision signal source and a low-precision measuring device are adopted.
Preferably, the signal source is used to generate the input signal required for amplifier testing, including but not limited to digital-to-analog converters (DACs), commercial signal sources, function generators, etc.; any circuit, instrument, device, or the like capable of providing a sinusoidal signal can be considered a signal source.
Preferably, the signal source adopted by the invention does not need to meet the requirement that the precision of the signal source is at least 3 to 4 bits higher than that of the circuit to be tested, which is specified by the IEEE standard, the precision of the signal source can be lower than that of the IEEE standard, and the THD value of the signal source can be at most about 60dB higher than that of the IEEE standard by taking the THD value as an example.
Preferably, the multipath filter group A and the multipath filter group B are respectively formed by a plurality of filters and switches and are used for respectively carrying out filtering processing on the output signals of the signal source and the output signals of the tested amplifier so as to generate a plurality of groups of frequency spectrum related output signals;
the spectrum correlation of the output signals means that the filtered output signals can be related by the transfer function of the filter, so that in the subsequent data processing, the spectrum parameters of the tested amplifier, such as THD, SFDR, etc., can be calculated by using the spectrum correlation between the output signals.
Preferably, the filter satisfies 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; filters including, but not limited to, RC low pass filters, resistive attenuators, etc., may be used as filters in any circuit that has the function of changing the amplitude, frequency, and/or phase characteristics of a signal;
In particular, the direct path may also be regarded as a filter.
Preferably, the switch is used to change the filtering paths of the above-mentioned multipath filter bank a and multipath filter bank B, and the switch may be a multiplexer or a plurality of switches, and the linearity of the switch should not be lower than that of the amplifier to be tested, so as to avoid introducing additional distortion components.
Preferably, the multipath filter group at least comprises two paths, and the paths can be added according to actual conditions, and the multipath filter group needs to meet the following three requirements: (1) The linearity of the multipath filter bank is high, and the linearity of the multipath filter bank is not lower than that of the amplifier to be tested so as to avoid introducing additional distortion components; (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.
Preferably, the circuit structure of the multipath filter bank a and the circuit structure of the multipath filter bank B may be the same or different;
the measuring device is used for converting the analog signal into a digital signal; measurement devices including, but not limited to, ADCs, spectrum analyzers, etc., any circuit, instrument, device, etc. that has the function of converting an analog signal to a digital signal may be considered a measurement device.
Preferably, the measuring device adopted by the invention does not need to meet the requirement that the precision of the circuit to be measured is at least 3 to 4 bits higher than that of the circuit to be measured, the precision of the measuring device can be lower than that of the IEEE standard, and the resolution of the measuring device adopted by the invention can be at most about 6 bits lower than that of the IEEE standard by taking resolution as an example. Preferably, the data processing module is used for obtaining the dynamic parameter index for evaluating the spectral characteristics of the tested amplifier finally by utilizing the algorithm provided by the invention according to a plurality of groups of output data acquired by the measuring device and combining the transfer function of the known multipath filter group; the data processing module should have the ability to execute algorithms, store data. The data processing module includes, but is not limited to, a computer, FPGA, DSP, etc.
To achieve the above and other related objects, in a second aspect, an embodiment of the present invention provides an amplifier testing method, which specifically includes the following steps:
the first step, prepare before making the test, include: selecting a proper multipath filter bank; editing a test program in a data processing module; the device comprises a signal source, a multipath filter bank A, a tested amplifier, a multipath filter bank B, a measuring device and a data processing module;
selecting a filtering path of the multipath filter bank A and a filtering path of the multipath filter bank B, connecting the two filtering paths with a signal source, a tested amplifier and a measuring device to form a group of testing paths, and recording the selected filters;
Thirdly, the signal source generates a group of input signals, the input signals enter the tested amplifier after being filtered by the multipath filter bank A, the tested amplifier is excited, 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, so that test data of the group of filter paths are obtained;
Fourth, the data processing module receives and stores the test data acquired by the measuring device;
fifthly, changing the filter paths in the multipath filter bank A and/or the multipath filter bank B to form another group of test paths, and recording the selected filters;
A sixth step of generating signals with the same amplitude, frequency and initial phase as the first group of input signals by using a signal source, and repeating the third step, the fourth step and the fifth step until test data of a sufficient number of different filter paths are acquired; the number of sets of test data is determined by the number of filters comprised by the multiple filter bank A and the multiple filter bank B, e.g. the multiple filter bank A comprises n (n.gtoreq.2) filter paths and the multiple filter bank B comprises s (s.gtoreq.2) filter paths, the number of sets of test data required is at least 3 and at most n x s sets, wherein the filter paths of the multiple filter bank A are changed at least 1 time and the filter paths of the multiple filter bank B are changed at least 1 time.
Seventh, in the data processing module, the collected data is processed. When the multipath filter group A and the multipath filter group B respectively comprise two filter paths, the harmonic calculation formula of the tested amplifier has four expression forms, any expression form is selected, the harmonic information of the tested amplifier can be calculated, and the four calculation formulas 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,fin is the frequency of the input signal; h m1k、hm2k、hm3k 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 represents output data collected by the measuring device when the filter 2 and the filter 4 are selected to be connected in a path;
the total harmonic distortion THD and spurious free dynamic range SFDR of the tested amplifier are calculated as:
THD＝10log10(∑k≥2|2huk|2) (5)
As shown in fig. 2, when the accuracy requirement of the amplifier test on the signal source is only reduced, a multipath filter bank a can be arranged between the signal source and the tested amplifier, and the amplifier is tested by adopting a low-accuracy signal source and a high-accuracy measuring device, specifically:
1. The invention uses the high-precision measuring device meeting the IEEE standard precision requirement to test the amplifier, namely the distortion of the measuring device is at least ten times or 20dB lower than the distortion of the measured amplifier, so as to avoid the nonlinear distortion of the measuring device from deteriorating the output of the measured amplifier.
2. The invention can further reduce the precision requirement of the amplifier test on the signal source, and compared with the precision requirement of the IEEE standard, the invention can reduce the precision requirement of the amplifier test on the signal source by at most about 80dB;
3. The test steps of the amplifier test circuit are specifically as follows:
3.1 the multipath filter group A comprises n filter paths, one filter path in the n filter paths of the multipath filter group 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;
3.2 the signal source generates a group of input signals, after the input signals are filtered by the multipath filter bank A, the tested amplifier is excited, 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;
3.3 changing the filter path of the multipath filter group A to form another group of amplifier test circuits and recording the selected filter path;
3.4 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 3.2 and 3.3, changing the filtering paths of the multipath filter group A at least 1 time, and collecting test data of at least 2 groups of different filtering paths.
4. When the multipath filter group A comprises two filtering paths and the acquired test data is 2 groups, the harmonic calculation formula for calculating the tested amplifier has the following two expression forms, and any one can be selected to calculate the harmonic information of the tested amplifier. The two calculation formulas are respectively as follows:
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 a, respectively; ω is the turning frequency of the filter, ω=2×pi×f in,fin 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 represents output data collected by the measuring device when the selection filter 2 is connected in the path;
As shown in fig. 3, when the accuracy requirement of the amplifier test on the measuring device is only reduced, a multipath filter bank B can be arranged between the tested amplifier and the measuring device, and a high-accuracy signal source and a low-accuracy measuring device are adopted, specifically:
1. the invention uses the high-precision signal source meeting the IEEE standard precision requirement to test the amplifier, namely the distortion of the signal source is at least ten times or 20dB lower than that of the tested amplifier, so as to avoid the nonlinear distortion of the signal source from deteriorating the output of the tested amplifier.
2. The invention can further reduce the precision requirement of the amplifier test on the measuring device, and compared with the precision requirement of the IEEE standard, the invention can reduce the precision requirement of the amplifier test on the measuring device by at most about 8 bits;
3. The test steps of the amplifier test circuit are specifically as follows:
3.1 the multipath filter group B comprises s filter paths, one filter path of the s filter paths in the multipath filter group 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;
3.2, the signal source generates a group of input signals, the input signals enter the tested amplifier 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;
3.3 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;
3.4 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 3.2 and 3.3, changing the filtering paths of the multipath filter bank B at least 1 time, and collecting test data of at least 2 groups of different filtering paths.
4. When the multipath filter bank B comprises two filter paths and the collected test data is 2 sets, the harmonic calculation formula for calculating the tested amplifier has the following expression form:
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 B, respectively; ω is the turning frequency of the filter, ω=2×pi×f in,fin 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.
Example 1
The invention provides an amplifier test circuit and a test method, which are used for reducing the precision requirements of amplifier test on a signal source and a measuring device, as shown in fig. 4, and specifically comprise the following steps:
first, in this embodiment, the multiple filter bank a and the multiple filter bank B have the same circuit structure; the multipath filter bank A is formed by connecting a filter 1 and a filter 2 in parallel, and the multipath filter bank B is formed by connecting a filter 3 and a filter 4 in parallel; the filters 1 and 3 are first order low pass RC filters, the transfer function of which can be expressed as
Where ω 0 is the turning frequency of the filter 1,R L and C L are the resistance and capacitance, respectively, that make up the first order low pass RC filter.
Filter 2 and filter 4 are resistive attenuators, the transfer function of which can be expressed as
Where R 1 and R 2 are the resistances that make up the resistive attenuator.
A second step of selecting a suitable signal source and measuring device, for example, selecting a signal source with THD value about 60dB higher than the IEEE standard precision requirement, selecting an ADC with precision about 4 bits lower than the IEEE standard precision requirement;
Third, the connection circuit, ready for testing, comprises: editing a test program in a data processing module; the device comprises a signal source, a multipath filter bank A, a tested amplifier, a multipath filter bank B, a measuring device and a data processing module;
A filter 1 passage of the multipath filter bank A and a filter 3 passage of the multipath filter bank B are selected, the filter 1 passage and the filter 3 passage are connected with the signal source, the amplifier to be tested and the measuring device to form a first group of test passages, and the selected filter passages are recorded;
Fifthly, the signal source generates a group of input signals, the input signals are filtered by the multipath filter bank A, the filtered input signals excite the tested amplifier, the output signals of the tested amplifier are filtered by the multipath filter bank B and then input into the measuring device, and the measuring device converts analog signals into digital signals and transmits the digital signals to the data processing module;
A sixth step, the data processing module receives the digital signal output by the measuring device and stores the group of data as m 1;
A seventh step of changing the selection of filter paths in the multipath filter bank A and the multipath filter bank B through a switch, selecting a filter 1 path of the multipath filter bank A and a filter 4 path of the multipath filter bank B, connecting the filter 1 path, the filter 4 path, a signal source, a tested amplifier and a measuring device into a second group of test paths, recording the selected filter, generating signals with the same amplitude, frequency and initial phase as those of the first group of input signals by using the signal source, and repeating the fifth step and the sixth step, and recording the reorganized data as m 2;
Eighth, changing the selection of filter paths in a multi-path filter bank A and a multi-path filter bank B through a switch, selecting a filter 2 path of the multi-path filter bank A and a filter 3 path of the multi-path filter bank B, connecting the filter 2 path, the filter 3 path, a signal source, a tested amplifier and a measuring device into a third set of test paths, recording the selected filter, generating signals with the same amplitude, frequency and initial phase as those of the first set of input signals by using the signal source, and repeating the fifth step and the sixth step, wherein the recorded reorganized data is m 3;
ninth, in the data processing module, processing the collected data (m 1、m2 and m 3); the harmonic calculation form of the tested amplifier is expressed as follows:
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,fin is the frequency of the input signal; h m1k、hm2k and h m3k are the spectral lines of the kth harmonic of the test data m 1、m2 and m 3, 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;
the total harmonic distortion THD and spurious free dynamic range SFDR of the tested amplifier are calculated as:
THD＝10log10(∑k≥2|2huk|2) (5)
Fig. 7 is a graph of simulation results of testing an amplifier having a THD value of-121.42 dB using a signal source having a THD value of-79.76 dB and a measuring device having a THD value of-118.13 dB in accordance with the circuit and method provided by the present invention. In the figure, the x-axis represents normalized frequency, the y-axis represents normalized power, the frequency spectrum marked with an asterisk represents the real spectrogram of the amplifier under test, and the frequency spectrum marked with a circle represents the simulated spectrogram obtained according to the method of the invention. To accurately test the spectral performance of an amplifier with a THD value of-121.42 dB, the traditional method requires that the THD value of the signal source and the measuring device be as low as-140 dB, which not only requires expensive testing instruments, but also is hardly realized on-chip testing. The method provided by the invention only adopts a signal source with the THD value of-79.76 dB and a measuring device with the THD value of-118.13 dB to test the amplifier with the THD value of-121.42 dB, and the method has the same test precision as the traditional method. Compared with the traditional method, the method can reduce the precision requirement of the amplifier test on the signal source by about 60dB under the condition of obtaining the accurate test result, and reduce the precision requirement of the amplifier test on the measuring device by about 20dB, thereby remarkably reducing the requirement on a precision test instrument and greatly reducing the test cost.
Fig. 8 is a diagram of simulation results of testing a low distortion amplifier using a low precision signal source and a low precision measurement device randomly in 500 simulations according to the circuit and method provided by the present invention. In the simulation, the total harmonic distortion of the amplifier was randomly generated in the range of-125 dB to-115 dB. In the figure, the x-axis represents the THD value of the tested amplifier, the y-axis represents the THD error value of the tested amplifier obtained by the invention, and the asterisk marks represent the single simulation result. As can be seen from the graph, the THD value of the amplifier measured by the method of the present invention has a small error with the true value, and the maximum error is only 0.97dB.
Example 2
The invention provides an amplifier test circuit and a test method, which are used for reducing the precision requirement of amplifier test on a signal source, as shown in fig. 5, and specifically comprise the following steps:
In the first step, in the present embodiment, the multipath filter bank a is formed by connecting the filter 1 and the filter 2 in parallel, where the filter 1 is a second-order low-pass RC filter, and its transfer function can be expressed as:
wherein omega n is the natural angular frequency, Zeta is the damping coefficient of the material,R L1、RL2、CL1 and C L2 are the resistance and capacitance, respectively, that make up the second order low pass RC filter.
The filter 2 is a resistive attenuator, the transfer function of which can be expressed as:
Where R 1 and R 2 are the resistances that make up the resistive attenuator.
A second step of selecting a proper signal source and measuring device, for example, selecting a signal source with THD value about 70dB higher than the IEEE standard precision requirement, selecting an ADC with precision meeting the IEEE standard precision requirement;
third, the connection circuit, ready for testing, comprises: editing a test program in a data processing module; the device comprises a signal source, a multipath filter group A, a tested amplifier, a measuring device and a data processing module, wherein the signal source, the multipath filter group A, the tested amplifier, the measuring device and the data processing module are connected;
step four, selecting a filter 1 passage of a multipath filter bank A, connecting the signal source, the amplifier to be tested and the measuring device into a first group of test passages, and recording the selected filter passage;
Fifthly, the signal source generates a group of input signals, the input signals are filtered by the multipath filter bank A, the filtered input signals excite the tested amplifier, the output signals of the tested amplifier are input into the measuring device, and the measuring device converts analog signals into digital signals and transmits the digital signals to the data processing module;
A sixth step, the data processing module receives the digital signal output by the measuring device and stores the group of data as m 1;
A seventh step of changing a filtering path of the multipath filter bank A through a switch, selecting a filter 2 path of the multipath filter bank A, connecting the multipath filter bank A with a signal source, a tested amplifier and a measuring device to form a second group of testing paths, recording the selected filter, generating signals with the same amplitude, frequency and initial phase as those of the first group of input signals by using the signal source, and repeating the fifth step and the sixth step, wherein the recorded reorganized data is m 2;
Eighth, in the data processing module, processing the collected data (m 1 and m 2); the harmonic calculation formula of the tested amplifier has two expression forms, any one expression form is selected, the harmonic spectral line of the tested amplifier can be calculated, and the two calculation formulas 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 a, respectively; ω is the turning frequency of the filter, ω=2×pi×f in,fin 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 represents output data collected by the measuring device when the selection filter 2 is connected in the path;
the total harmonic distortion THD and spurious free dynamic range SFDR of the tested amplifier are calculated as:
THD＝10log10(∑k≥2|2huk|2) (5)
Fig. 9 is a graph of simulation results from testing an amplifier having a THD value of-118.08 dB using a signal source having a THD value of-67.72 dB in accordance with the circuit and method provided by the present invention. In the figure, the x-axis represents normalized frequency, the y-axis represents normalized power, the frequency spectrum marked with an asterisk represents the real spectrogram of the amplifier under test, and the frequency spectrum marked with a circle represents the simulated spectrogram obtained according to the method of the invention. To test the spectral characteristics of an amplifier with a THD value of-118.08 dB, the conventional method requires that the THD value of the signal source is as low as about-140 dB, which is hardly achievable for existing high-precision signal sources, to generate such low-distortion signals. The method provided by the invention only adopts a signal source with the THD value of-67.72 dB to test the amplifier with the THD value of-118.08 dB, and the method has the same test precision as the traditional method. Compared with the traditional method, the method can reduce the precision requirement of the amplifier test on the signal source by about 70dB under the condition of obtaining the accurate test result, and obviously reduces the requirement of the amplifier test on a precise instrument, thereby greatly reducing the test cost.
Example 3
When the amplifier testing circuit provided by the invention is used for testing an amplifier, as shown in fig. 6, the method specifically comprises the following steps:
In the present embodiment, the multipath filter bank B is formed by connecting a filter 1 and a filter 2 in parallel, wherein the filter 1 is an active first-order low-pass RC filter, and the transfer function thereof can be expressed as follows;
Where ω 0 is the turning frequency of the filter 1, R L1、RL2、RL3 and C L are the resistance and capacitance, respectively, that make up the active first order low pass RC filter.
The filter 2 is a direct path whose transfer function can be expressed as
H2(jω)＝1
Selecting a proper signal source and a proper measuring device, for example, selecting a signal source with THD value meeting the precision requirement of the IEEE standard, and selecting an ADC with the precision about 8 bits lower than the precision requirement of the IEEE standard;
Third, the connection circuit, ready for testing, comprises: editing a test program in a data processing module; the device comprises a signal source, a tested amplifier, a multipath filter bank B, a measuring device and a data processing module;
Step four, selecting a filter 1 passage of a multipath filter bank B, connecting the signal source, the tested amplifier and the measuring device into a first group of test passages, and recording the selected filter passage;
fifthly, 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, the filtered input signals are input into the measuring device, and the measuring device converts analog signals into digital signals and transmits the digital signals to the data processing module;
A sixth step, the data processing module receives the digital signal output by the measuring device and stores the group of data as m 1;
A seventh step of changing the filtering path of the multipath filter bank through a switch, selecting the filter 2 path of the multipath filter bank B, connecting the multipath filter bank B with a signal source, a tested amplifier and a measuring device to form a second group of testing paths, recording the selected filter, generating signals with the same amplitude, frequency and initial phase as those of the first group of input signals by using the signal source, and repeating the fifth step and the sixth step, wherein the recorded reorganized data is m 2;
Eighth, in the data processing module, processing the collected data (m 1 and m 2); 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 B, respectively; ω is the turning frequency of the filter, ω=2×pi×f in,fin 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.
The total harmonic distortion THD and spurious free dynamic range SFDR of the tested amplifier are calculated as:
THD＝10log10(∑k≥2|2huk|2) (5)
Fig. 10 is a graph of simulation results of testing an amplifier having a THD value of-119.70 dB using a 14-bit precision measurement device in accordance with the circuit and method provided by the present invention. In the figure, the x-axis represents normalized frequency, the y-axis represents normalized power, the frequency spectrum marked with an asterisk represents the real spectrogram of the amplifier under test, and the frequency spectrum marked with a circle represents the simulated spectrogram obtained according to the method of the invention. To accurately test the spectral performance of an amplifier having a THD value of-119.70 dB, conventional methods require that the accuracy of the measurement device be at least 22 bits, while existing measurement devices are typically faced with a compromise in accuracy versus speed, bandwidth, etc. The method provided by the invention can test the amplifier with the THD value of-119.70 dB by adopting a 14-bit measuring device, and the method has the same test precision as the traditional method. Compared with the traditional method, the method can reduce the precision requirement of the amplifier test on the measuring device by about 8 bits under the condition of obtaining the accurate test result, and obviously reduces the requirement of the amplifier test on the accurate test instrument, thereby greatly reducing the test cost.
Therefore, the invention can obviously reduce the precision requirement of the amplifier test on the signal source and/or the measuring device, thereby greatly reducing the test cost of the amplifier test, solving the problem that a high-precision test instrument is difficult to obtain in the ultralow distortion amplifier test and providing a feasible solution for the on-chip test of the amplifier.
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,fin is the frequency of the input signal; h m1k、hm2k、hm3k 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,fin 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,fin 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.
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