KR100241787B1 - Automatic frequency control arrangement for superheterodyne receiver - Google Patents

Abstract

The present invention relates to an automatic frequency control device for a superheterodyne receiver.

An apparatus for automatic frequency control of a superheterodyne type receiver which receives a frequency shift keying modulated signal, mixes with a predetermined local oscillation frequency signal generated by a local oscillator, and then takes only an intermediate frequency to demodulate original data. A sampling unit for continuously sampling the demodulated data for one period and a duty measurement unit for detecting a difference in duty when the demodulated data is in a high state and a low state by inputting sampling data output from the sampling unit; And a digital / analog converter for converting the detected duty difference into an analog signal and feeding back to the local oscillator as a frequency adjustment signal.

Description

Automatic Frequency Control Unit of Superheterodyne Receiver

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for automatic frequency control (hereinafter referred to as AFC) in a wireless communication terminal, and more particularly, to an AFC apparatus and method by duty determination of demodulated data.

In order to receive a signal modulated by frequency shift keying (FSK), a superheterodyne or a homodyne method is used.

1 is a block diagram showing the configuration of a conventional homodyne receiver.

The signal FC received at the homodyne receiver is the FSK frequency modulated with a constant deviation. The local oscillator 12 generates a local oscillation frequency signal FL having the same frequency as the received signal FC. A mixer 11 mixes the received signal FC with a local oscillation frequency signal FL. The channel filter 13 filters only components corresponding to a desired signal, that is, a deviation, from the output of the mixer 11. The demodulator 14 demodulates the original data from the signal filtered by the channel filter 13. The above is a part included in the reference numeral 100 and is a component of a basic homodyne receiver. As shown here, the first and second counters 15 and 16, a comparator 17, and a digital / analog (hereinafter referred to as D / A), are further provided with a conversion unit 18. Is for automatic frequency control.

Since the data DATA demodulated by the demodulator 14 is an FSK signal, the high and low states are repeated. The first counter 15 counts the frequency generated by the channel filter 13 while the data DATA is in the high state. The second counter 16 counts the frequency generated by the channel filter 13 while the data DATA is low. The comparator 17 compares the number counted by the first and second counters 15 and 16 and outputs a predetermined comparison signal having a digital form according to the comparison result. The D / A converter 18 converts the comparison signal into an analog form. The comparison signal converted into the analog form is fed back to the local oscillator 12 to correct the frequency of the local oscillator 12, and this operation is repeated until the correct frequency.

The reason why the frequency of the local oscillator 12 becomes inaccurate is due to temperature or other environmental factors. Figure 2 shows the data recovery form when the local oscillation frequency is generated correctly and the form of the baseband signal, Figure 3 shows the data recovery form when the local oscillation frequency is generated incorrectly and the form of the baseband signal It is shown.

Referring to FIG. 2, when the frequency FL generated from the local oscillator 12 is exactly positioned at the center as shown in 2A, the high state and the low state are shown as shown in 2B. The demodulation data DATA having the same duration and the baseband signal in each state, that is, the output of the channel filter 13 can be obtained.

Referring to FIG. 3, when the frequency FL generated from the local oscillator 12 deviates from the center for some reason as shown in (3A), the demodulation data DATA is high as shown in (3B). While maintaining the state, the frequency of the baseband signal output from the channel filter 13 decreases than normal and increases while maintaining the low state.

In order to demodulate desired data in the homodyne receiver, a baseband signal corresponding to a deviation is essential. This is because desired AFC operation is performed using the frequency difference of the baseband signal.

However, the super heterodyne reception method is a method of mixing and detecting a high frequency signal induced in an antenna circuit with a high frequency signal oscillated by a local oscillator in a receiver and converting it into an intermediate frequency, which is a difference between two high frequencies, to receive and amplify and detect it. Due to this characteristic, there is no baseband signal, and therefore, the AFC operation cannot be performed in the superheterodyne receiver like the aforementioned homodyne receiver.

Accordingly, an object of the present invention is to provide an automatic frequency control apparatus for a superheterodyne receiver.

The present invention for achieving the above object is a superheterodyne receiver for receiving a frequency shift keying modulated signal, mixing with a predetermined local oscillation frequency signal generated in the local oscillator and then taking only the intermediate frequency to demodulate the original data. An automatic frequency control apparatus comprising: a sampling unit for continuously sampling the demodulated data for one period; and a duty when the demodulated data is in a high state and a low state by inputting sampling data output from the sampling unit; And a duty measuring unit for detecting a difference, and a digital / analog converter for converting the detected duty difference into an analog signal and feeding back the local oscillator as a frequency adjustment signal.

1 is a block diagram showing the configuration of a conventional homodyne receiver

2 is a diagram illustrating a form of data recovery and a form of a baseband signal when a local oscillation frequency is generated accurately;

3 is a diagram illustrating a form of data recovery and a form of a baseband signal when a local oscillation frequency is incorrectly generated;

4 is a block diagram showing the configuration of a superheterodyne receiver according to an embodiment of the present invention.

5 is a diagram illustrating a data recovery form and a sampling data count thereof when a local oscillation frequency is generated correctly;

6 is a diagram illustrating a data recovery form and a sampling data count thereof when a local oscillation frequency is generated correctly;

7 illustrates a duty recovery procedure in a data stream.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, numerous specific details such as components of specific circuits are shown, which are provided to help a more general understanding of the present invention, and it is understood that the present invention may be practiced without these specific details. It will be self-evident to those of ordinary knowledge. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

4 is a block diagram showing the configuration of a superheterodyne receiver according to an embodiment of the present invention.

When the superheterodyne receiver receives a signal that is FSK modulated and transmitted, the mixer 41 mixes the frequency FC of the received signal with a predetermined local oscillation frequency FL. The local oscillator 42 generates a local oscillation frequency FL that is different from the reception frequency FC and the intermediate frequency IF so that the receiver can receive a desired signal. The local oscillator 42 is connected to a crystal 43 and a varactor 44. The varactor 44 may control a frequency by changing an internal capacitance value according to an input voltage. The intermediate frequency filter 45 is connected to the output terminal of the mixer 41 to take only the intermediate frequency of the output of the mixer 41. The demodulator 46 inputs the intermediate frequency to demodulate the original data. The sampling unit 47 inputs and demodulates the demodulated data.

The duty measuring unit 200 inputs sampling data output from the sampling unit 47 to detect a difference in duty when the demodulated data DATA is in a high state and a low state. Specifically, in order to determine the duty of the demodulated data DATA, it is necessary to check the duration in each state by using a clock higher than the data rate, and one period of data input by the sampling unit 47 is input. If sampling is performed continuously during the time period, it is possible to know how many sampling data are detected in the high state and how many sampling data are detected in the low state. The first counter 48 counts the number of sampling data for the data in the high state. The second counter 49 counts the number of sampling data for the low state data. The comparator 50 compares the number counted by the first and second counters 48 and 49 and outputs a comparison signal having a predetermined value according to the result. The temporary memory unit 51 temporarily stores the value output from the comparator 50.

The D / A converter 52 converts the digital value output from the temporary memory 51 into an analog form. This converted analog value is applied to the varactor 44 to precisely adjust the frequency of the local oscillator 42 by increasing or decreasing the frequency.

Fig. 5 shows the data recovery form when the local oscillation frequency is generated correctly and its sampling data count value.

When the local oscillation frequency FL generated by the local oscillator 42 is exactly centered, the difference between the center frequency FL and both deviation frequencies FL + 4.5KHz and FL-4.5KHz is exactly the same. do. Therefore, the number of sampling data counted by the first and second counters 48 and 49 also exactly matches. In conclusion, in such a case, it is not necessary to adjust the frequency of the local oscillator 42.

Fig. 6 shows the data recovery form when the local oscillation frequency is incorrectly generated and its sampling data count value.

The illustrated form assumes that the local oscillation frequency FL that occurs in the local oscillator 42 is not centered correctly and has been turned to the right. In this case, data having a duration proportional to the frequency difference is output due to the characteristics of the demodulation unit 46 of the quadrature detection method using an intermediate frequency. That is, since the interval between the center frequency FL + Δf and the right deviation frequency FL + 4.5KHz is narrow, the duration is small, and the distance between the left deviation frequency FL-4.5KHz is wide and the duration is large. Therefore, the demodulated data waveform is not normally duty as shown.

However, conventional demodulators have a built-in quick charge circuit to compensate for this duration. Specifically, by shifting the reference voltage to maintain the correct duty after a certain time has elapsed. Therefore, it is difficult to know how far the local oscillation frequency is from the center. 7 is a diagram illustrating a duty recovery procedure in a data stream.

In this embodiment, a part in which a high state and a low state are alternately repeated (for example, a preamble portion of a POCSAG code) of a data stream is used to know how far from the center the local oscillation frequency is. The result of sampling only the first few bits is stored in the temporary storage unit 51. This value is converted into analog form by the D / A converter 52 and then applied to the varactor 44 to accurately adjust the frequency of the local oscillator 42 by increasing or decreasing the frequency. The value stored in the temporary memory unit 51 is maintained until it is changed to the next new value. Only the moment of initial power on is stored as a new value, so there is no fear of changing the data processing period.

In the case of FIG. 6 described above, the local oscillator 42 is increased by increasing the capacitance of the varactor 44 such that the analog value output from the digital / analog converter 52 has a form of a reduced voltage than before. This reduces the frequency deviation of.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention facilitates automatic frequency control of a superheterodyne receiver by recognizing a change in frequency through duty determination of demodulated data. In addition, since ASIC can be converted from sampling to analog conversion, it is effective to reduce the volume of the terminal when implemented in a single chip. In addition, even with low-cost crystals with large temperature variations, this automatic frequency control can reduce the variation, which is effective in reducing the manufacturing cost of the receiver.

Claims (6)

In the automatic frequency control apparatus of a superheterodyne type receiver which receives a frequency shift keying modulated signal, mixes with a predetermined local oscillation frequency signal generated by a local oscillator, and then takes only an intermediate frequency to demodulate original data. A sampling unit for continuously sampling the demodulated data for one period; A duty measurement unit configured to input sampling data output from the sampling unit to detect a difference in duty when the demodulated data is in a high state and a low state; And a digital / analog converter for converting the detected duty difference into an analog signal and feeding back the frequency oscillator to the local oscillator as a frequency adjustment signal. The method of claim 1, wherein the duty measurement unit, A first counter for counting the number of sampling data detected in the high state of the demodulated data; A second counter for counting the number of sampling data detected in a low state of the demodulated data; And a comparator for comparing the counts counted by the first and second counters and outputting a comparison signal having a predetermined value according to the result. The method of claim 2, wherein the duty measuring unit, And a temporary memory unit for temporarily storing the comparison signal output from the comparator. The method of claim 2, And a varactor that adjusts the frequency of the local oscillator by increasing or decreasing the frequency by changing an internal capacitance value according to the analog type comparison signal. The method of claim 1, The local oscillator is connected to a crystal. In the automatic frequency control apparatus of a superheterodyne receiver for receiving a frequency shift keying modulated signal, A local oscillator for generating a predetermined local oscillation frequency signal having a difference between the frequency of the received signal and the intermediate frequency; A mixer for mixing a received signal and the local oscillation frequency signal; An intermediate frequency filter connected to an output of the mixer and taking only an intermediate frequency of the output of the mixer; A demodulator for demodulating original data by inputting the intermediate frequency; A sampling unit for continuously sampling the demodulated data for one period; A first counter for counting the number of sampling data detected in the high state of the demodulated data; A second counter for counting the number of sampling data detected in a low state of the demodulated data; A comparator for comparing the number counted by the first and second counters and outputting a comparison signal having a predetermined value according to the result; A temporary memory unit for temporarily storing the comparison signal output from the comparator; A digital / analog converter for converting a digital comparison signal output from the temporary memory unit into an analog form; And a varactor that adjusts the frequency of the local oscillator by increasing or decreasing the frequency by changing an internal capacitance value according to the analog type comparison signal.

Images