JP3766172B2 - Automatic frequency adjustment device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic frequency adjustment circuit using a digital circuit.
[0002]
[Prior art]
A conventional automatic frequency adjusting device will be described with reference to FIG. The frequency converter 12 frequency-converts the received signal input from the input terminal 11 and the oscillation signal from the oscillator 13 whose oscillation frequency can be varied, and the amplitude of the frequency-converted signal is made constant by the automatic gain control device 34. Output. A signal having a constant amplitude is branched, one is output from the output terminal 15 and the other is input to the counter 16 where it is counted. The output of the counter 16 is averaged by the filter 17. The control circuit 18 detects a frequency shift with respect to the set frequency of the signal after frequency conversion based on the signal averaged by the filter 17, controls the oscillation frequency of the oscillator 13, and adjusts the frequency after frequency conversion to the set frequency. I do.
[0003]
In such an automatic frequency adjusting device, when the received signal is low C / N and the noise is relatively large compared to the originally required signal, there is a problem that the count error occurs due to the noise and the frequency deviates from the set frequency. there were.
[0004]
In addition, as shown in FIG. 6, when a hysteresis comparator 39 having a hysteresis width fixed at an arbitrary value is inserted in the preceding stage of the counter 16 in order to reduce a count error due to noise, the count error due to noise is reduced. However, the automatic gain control device 34 has a range of signal levels at which the amplitude can be kept constant, and the amplitude of the signal output from the automatic gain control device 34 decreases or increases outside the range. End up.
[0005]
Here, consider a case where the received signal is small and the output signal amplitude of the automatic gain control device 34 cannot be amplified to a certain level, and the output amplitude decreases. At this time, if the amplitude of the signal is smaller than the hysteresis width arbitrarily set by the hysteresis comparator 39 in the subsequent stage of the automatic gain control device 34, the signal value after the comparison does not appear, and the frequency automatic There was a problem that the feedback function of adjustment stopped.
[0006]
[Problems to be solved by the invention]
In the conventional device described above, when a hysteresis comparator is inserted in front of the counter in order to reduce the frequency shift problem due to a count error caused by noise when the received signal is low C / N, or to reduce the count error due to noise. However, when the amplitude decreases outside the operable signal level range of the automatic gain control device and the signal amplitude becomes smaller than the hysteresis width, the feedback function of automatic frequency adjustment is stopped.
[0007]
The present invention is intended to reduce the frequency shift due to a count error caused by noise and prevent the automatic frequency adjustment feedback function from stopping even outside the operable signal level range of the automatic gain control device.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention inputs a received signal and an oscillation signal from an oscillator whose oscillation frequency is variable, respectively, and performs frequency conversion, and is arranged in an output signal path from the frequency converter. An automatic gain control device that controls a gain control amplifier by a gain control signal that changes according to a signal level passing through an output signal path and outputs a signal having a constant amplitude, and an output signal path. A comparator that compares the signal that passes through and the gain control signal, generates a pulse output whose hysteresis width changes according to the gain control signal, and inputs the pulse output from the hysteresis comparator. A counter for counting, a filter for inputting and averaging the output signal of the counter, and a frequency based on the output signal of the filter. Detecting a frequency shift with respect to the set frequency of the converted signal, characterized by comprising a control circuit for controlling the oscillation frequency of the oscillator.
[0009]
By taking such measures, the hysteresis width is varied by the control signal from the automatic gain controller while reducing the frequency shift due to count errors caused by noise in the hysteresis comparator, so the automatic gain controller can operate. It can operate without stopping the feedback function of automatic frequency adjustment even outside the signal level range.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a circuit configuration diagram for explaining a first embodiment of the present invention. The frequency converter 12 converts the frequency of the received signal input from the input terminal 11 and the oscillation signal from the oscillator 13 whose oscillation frequency can be varied, and the amplitude of the frequency-converted signal is made constant by the automatic gain control device 14. Output. The signal whose amplitude is made constant is branched and outputted from the output terminal 15 and is also inputted to the hysteresis comparator 19 and compared with the hysteresis characteristic. This hysteresis width is varied by a control signal from the automatic gain control device 14. The signal after the comparison is input to the counter 16 and counted here. The output of the counter 16 is averaged by the filter 17. The control circuit 18 detects a frequency shift with respect to the set frequency of the signal after frequency conversion based on the signal averaged by the filter 17, controls the oscillation frequency of the oscillator 13, and matches the frequency after frequency conversion to the set frequency. Perform the action.
[0011]
In this embodiment, by providing the hysteresis comparator 19 in the previous stage of the counter 16, it is possible to reduce frequency deviation due to a count error caused by noise at the time of low C / N of the received signal. At the same time, even when the received signal is small and outside the operable signal level range of the automatic gain controller 14, the output from the automatic gain controller 14 can be controlled from the automatic gain controller 14 even if the output amplitude cannot be amplified to a certain level. Since the hysteresis width of the hysteresis comparator 19 is changed according to the signal, the operation can be performed without stopping the feedback function of the automatic frequency adjustment.
[0012]
An example of a hysteresis comparator that can vary the hysteresis width used in this embodiment is Japanese Patent Laid-Open No. 63-243762, and other examples include a full-wave rectifier circuit, a comparator, and a flip-flop. There is a configuration by the group.
[0013]
Next, the full-wave rectifier circuit, the comparator, and the flip-flop constitute a hysteresis comparator, and the full-wave rectifier circuit of the present invention shares the full-wave rectifier circuit in the automatic gain control device. A second embodiment will be described with reference to FIG. In the following description, the same components as those in the embodiment of FIG.
[0014]
The automatic gain control device 14a is configured as follows. An input signal is amplified and output by a gain control amplifier 20 capable of gain control. The output signal is also input to the full-wave rectifier circuit 21 where it is full-wave rectified. The signal after full-wave rectification is smoothed by the filter 22. The control circuit 23 controls the gain of the gain control amplifier 20 based on the smoothed signal and also outputs a control signal having a hysteresis width. The automatic gain control device 14a applies the gain control feedback of the gain control amplifier 20 as described above, and makes the signal amplitude amplified by the gain control amplifier 20 constant.
[0015]
From here, it demonstrates using FIG. 3 which showed the operation | movement concept of the hysteresis comparator. The output of the automatic gain control device 14a is output to the output terminal 15 and also input to the hysteresis comparator 19a. The input signal is input to the data input terminal of the flip-flop 24. The comparator 25 receives a signal after full-wave rectification of the full-wave rectifier circuit 21 in the automatic gain control device 14a and a control signal having a hysteresis width output from the control circuit 23.
[0016]
As shown in FIG. 3, the comparator 25 compares the full-wave rectified signal and the hysteresis width control signal, compares them, and outputs them. The output signal of the comparator 25 is input to the clock input terminal of the flip-flop 24. As shown in FIG. 3, the flip-flop 24 reads the output signal of the comparator 25, that is, the signal of the data input terminal in accordance with the clock input, and compares the data input terminal signal with the threshold voltage and outputs it.
[0017]
As can be seen from FIG. 3, the output signal of the flip-flop 24 is switched when the signal after full-wave rectification exceeds the control signal of the hysteresis width. In this way, a comparator operation can be equivalently realized with hysteresis characteristics for data input, and the voltage value of the hysteresis width control signal at the output of the control circuit 23 can be varied to change the comparator 25. Output signal, that is, the clock signal of the flip-flop 24 can be varied, and the data read timing of the flip-flop 24 changes, so that the hysteresis width can be equivalently varied.
[0018]
In the explanatory diagram of FIG. 3, a flip-flop whose output changes at the rising edge of the clock is used. However, even in a flip-flop whose output changes at the falling edge of the clock, for example, the output signal of the comparator 25 is inverted by an inverter. A hysteresis comparator can be configured by inputting it to the clock input terminal of the flip-flop.
[0019]
Further, in the above description, the automatic gain control device 14a is configured by feedback of feedback that applies feedback by looking at the signal amplified by the gain control amplifier 20, but the signal before the gain control amplifier 20 as shown in FIG. Thus, the hysteresis comparator can be configured in the same manner with the automatic gain control circuit 14b which is a feed-forward feedback for controlling the amplification signal of the gain control amplifier 20 and the control signal of the hysteresis width so that the control circuit 23b is commensurate with it.
[0020]
As described above, in the configuration in which the hysteresis comparator capable of varying the hysteresis width is the full-wave rectifier circuit, the comparator, and the flip-flop, the circuit is obtained by sharing the full-wave rectifier circuit with the automatic gain control device. This can be reduced and is advantageous for reducing power consumption.
[0021]
【The invention's effect】
As described above, by using the hysteresis comparator, the received signal is small and the automatic gain control device can operate while reducing the frequency shift due to the count error caused by noise when the received signal is low C / N. Even if the output amplitude of the automatic gain control device cannot be amplified to a certain level outside the level range, the hysteresis width of the hysteresis comparator is changed by the control signal from the automatic gain control device. It can operate without stopping the function.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram for explaining a first embodiment of the present invention;
FIG. 2 is a circuit configuration diagram for explaining a second embodiment of the present invention.
FIG. 3 is an explanatory diagram for explaining the operation of a hysteresis comparator.
FIG. 4 is a circuit configuration diagram for explaining a second embodiment of the present invention.
FIG. 5 is a circuit configuration diagram for explaining a conventional technique.
FIG. 6 is a circuit configuration diagram for explaining a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Input terminal, 12 ... Frequency converter, 13 ... Oscillator, 14, 14a, 14b, 34 ... Automatic gain control device, 15 ... Output terminal, 16 ... Counter, 17 ... Filter, 18 ... Control circuit, 19, 19a, 34 ... Hysteresis comparator, 20 ... Gain control amplifier, 21 ... Full wave rectifier circuit, 22 ... Filter, 23, 23b ... Control circuit, 24 ... Flip-flop, 25 ... Comparator.

Claims (2)

A reception signal, a frequency converter oscillation frequency inputs respectively the oscillation signal from the variable oscillator, the frequency conversion,
A signal having a constant amplitude, having a gain control amplifier arranged in an output signal path from the frequency converter, and controlling the gain control amplifier by a gain control signal that changes according to a signal level passing through the output signal path An automatic gain control device that outputs
A comparator that compares the gain control signal with a signal passing through the output signal path, and generates a pulse output whose hysteresis width varies according to the gain control signal ;
A counter for inputting the pulse output from the hysteresis comparator and counting the pulse output ;
A filter for inputting and averaging the output signal of the counter;
An automatic frequency adjusting apparatus comprising: a control circuit that detects a frequency shift with respect to a set frequency of a signal after frequency conversion based on an output signal of the filter and controls an oscillation frequency of the oscillator. The hysteresis comparator is
A full-wave rectification circuit for full-wave rectification of an input or output signal of a gain control amplifier disposed in the output signal path ;
A comparator that compares the output signal of the full-wave rectifier circuit with the gain control signal and outputs the comparison result ;
2. The automatic frequency adjustment according to claim 1, wherein the output of the comparator is a clock input and a flip-flop having an output signal having a constant amplitude by the automatic gain control device as a data input. apparatus.

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