JPH0222904A - Phase synchronous demodulator - Google Patents

Abstract

PURPOSE:To stably discriminate synchronization or not even at the time of input of a signal of low S/N by providing a band-pass filter in the synchronization discriminating circuit of a sweep circuit in a phase synchronizing loop. CONSTITUTION:A demodulator 1 and a digital sweep circuit 2 are provided. A filter 22 which is inserted to the route between a low frequency oscillator 21 and synchronization discriminating means 23 and 24 and has a frequency band near the oscillation frequency of the oscillator 21 as the pass band is provided to eliminate noise components which penetrate synchronization discriminating means 23 and 24 of the digital sweep circuit 2. Thus, the stable leading-in operation is performed even for a phase modulated wave input signal of low S/N to stably discriminate synchronization or not.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is applied to a phase modulation method. In particular, it relates to a demodulator with an added digital sweep circuit and a phase-locked loop.

〔overview〕

The present invention enables stable synchronization/asynchronous determination in a phase modulation demodulator having a phase-locked loop to which a digital sweep circuit is added by removing noise components that invade the synchronization determination means of the digital sweep circuit. It is something.

[Conventional technology]

Conventionally, as a demodulator used in a phase modulation method, a method has been used in which the output signal of a voltage controlled oscillator is phase-synchronized with the input signal. FIG. 3 shows an example of the configuration of this type of demodulator. As shown in FIG. 3, this circuit includes a phase-locked loop demodulator 1 consisting of a phase comparator 11, a carrier-wave regenerated signal processing circuit 12, a synthesizer 13, a low-pass filter 14, and a voltage-controlled oscillator 15; The carrier synchronized signal processing circuit includes a low frequency oscillator 21, a wave detector 23, a voltage comparator 24, a low frequency oscillator 25, a switch 26, a counter 27 consisting of a binary counter, and a digital sweep circuit 2 consisting of a digital-to-analog converter 28. The terminal 29 to which the output of the synthesizer 13 is connected is connected to the terminal 18 to which the input of the synthesizer 13 is connected.

The phase modulated wave human input signal a passes through the terminal 10 to the phase comparator 11.
The in-phase signal C and the orthogonal signal C, which are generated by phase comparison using mutually orthogonal carrier signals, are input to the carrier reproduction signal processing circuit 12 . In this circuit, the influence of the modulation signal is removed, and a DC voltage corresponding to the phase difference between the phase modulated wave input signal a and the reproduced carrier wave signal d output from the voltage controlled oscillator 15 is generated. This signal is synthesizer 1
3 and is connected to a low-pass filter 14, where high-frequency components are removed, and then connected to a voltage controlled oscillator 15.
The phase of the voltage controlled oscillator 15 is controlled to be synchronized with the phase of the phase modulated wave input signal a. Further, the output of the carrier wave regenerating signal processing circuit 12 is connected to the feedback loop for oscillating the low frequency oscillator 21 via terminals 17 and 20, and when the phase locked loop is synchronized, the oscillation is stopped and the locked loop is If it is out of place, it will oscillate.

The output of this low frequency oscillator 21 is detected by a detector 23,
The voltage comparator 24 determines the synchronization state. The signal output from the low frequency oscillator 25 is switched on and off using the output of the voltage comparator 24 as a control signal. This switch 26 is controlled so that it is closed in an asynchronous state and opened in a synchronous state. The switching output of the low frequency oscillator 25 is counted by a counter 27 having binary counters connected in cascade, converted into a several-bit parallel output, and then converted into an analog voltage by a digital-to-analog converter 28. The output of the digital-to-analog converter 28 is input to the synchronous loop of the demodulator 1 via terminals 29 and 18, and is added in the synthesizer 13, so that the recovered carrier signal d output from the voltage controlled oscillator 15 and the phase modulation input signal a are combined. Sweeps until synchronized.

[Problem that the invention seeks to solve]

However, in such conventional digital sweep demodulators,
When the S/N ratio of the phase modulated wave human input signal is high, sufficient sweeping and pulling characteristics are exhibited, but when the S/N ratio is low, noise is superimposed on the output of the low frequency oscillator 21, and the output of the detector 23 is also noisy. As a result, accurate synchronization judgment cannot be made and stable retracting operation cannot be performed.

The present invention aims to eliminate such drawbacks, and aims to provide a phase synchronization demodulator that can perform a stable pull-in operation even with a phase modulated wave input signal having a low S/N ratio.

[Means for solving problems]

The present invention provides a phase comparator to which a phase modulated wave signal arrives, a voltage controlled oscillator that provides a regenerated carrier wave signal to the phase comparator, and a phase modulated wave signal and a regenerated carrier wave signal based on the signal generated by the phase comparator. a carrier wave regenerating signal processing circuit that generates a phase difference signal equivalent to the phase difference between the two, an oscillator that oscillates in response to this phase difference signal, and synchronization of the phase modulated wave signal and the regenerated carrier signal based on the output level of this oscillator. A synchronization determination means for determining a state, a synchronization control signal generation means for generating a synchronization control signal based on the determination result of the synchronization determination means, and a signal related to a signal obtained by combining the synchronization control signal and a signal related to a phase difference signal. a phase synchronization demodulator, the filter being inserted in a path between the oscillator and the synchronization determining means, and having a pass band in a frequency band near the oscillation frequency of the oscillator. It is characterized by having the following.

[Effect]

Noise enters the oscillator via the carrier wave recovery signal processing circuit. This noise makes the judgment by the synchronization judgment means unstable, and in particular, when the S/N ratio of the phase modulated wave input signal is low, the synchronization pull-in operation becomes impossible.

A filter for removing this noise is provided before the synchronization determining means to ensure stable sweep and pull-in characteristics.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block configuration diagram showing the configuration of the first embodiment. This embodiment includes a demodulator 1 and a digital sweep circuit 2, as shown in FIG.
3, a low-pass filter 14, and a voltage-controlled oscillator 15, and the digital sweep circuit 2 includes a low-frequency oscillator 21.
, a bandpass filter 22 , a wave detector 13 , a voltage comparator 24 , a low frequency oscillator 25 , a switch 26 , a counter 27 in which binary counters are connected in cascade, and a digital-to-analog converter 28 . That is, this embodiment includes a phase comparator 11 to which a phase modulated wave signal arrives, a voltage controlled oscillator 15 that supplies a recovered carrier wave signal to this phase comparator 11, and a phase modulated wave signal based on the signal generated by the phase comparator 11. A carrier wave reproduction signal processing circuit 12 that generates a phase difference signal corresponding to the phase difference between the wave signal and the reproduction carrier wave signal, a low frequency oscillator 21 that is an oscillator that oscillates in response to this phase difference signal, and an output level of this oscillator. A detector 23 and a voltage comparator 24 are synchronization determining means for determining the synchronization state of the phase modulated wave signal and the reproduced carrier signal based on the synchronization determination means, and a synchronization control signal for generating a synchronization control signal based on the determination result of the synchronization determination means. A synthesizer that provides the voltage-controlled oscillator with a signal related to a signal obtained by combining the low-frequency oscillator 25, switch 26, counter 27, and digital-to-analog converter 28, which are generation means, and the synchronous control signal and a signal related to the phase difference signal. 13, and a band-pass filter 22 which is inserted in a path between the oscillator and the synchronization determination means and whose passband is a frequency band near the oscillation frequency of the oscillator.

Next, the operation of this embodiment will be explained. The phase modulated input signal a is input to the phase comparator 11 via the terminal 10, and the phases are compared using mutually orthogonal carrier signals, and the generated in-phase signal and orthogonal signal C are sent to the carrier-wave regenerated signal processing circuit 12.
Here, the influence of the modulated wave is removed and a DC control signal proportional to the phase difference between the phase modulated input signal a and the recovered carrier signal d is generated. The signal is applied to a pass-pass filter 14, where high-frequency noise is removed, and then the frequency and phase of a voltage controlled oscillator 150 are controlled. In this way, the regenerated carrier signal d, which is the output of the voltage controlled oscillator 15, can be synchronized with the phase modulated input signal a. Further, the output of the carrier wave regenerating signal processing circuit 12 is connected to the feedback loop of a low frequency oscillator 21, and the oscillator 21 is adjusted so that it oscillates when the phase-locked loop is asynchronous, and stops oscillating when it is synchronized. . The output of low frequency oscillator 25 is connected to bandpass filter 22 . After extracting only the signal near the oscillation frequency of the low frequency oscillator 21 from the signal output from the low frequency oscillator 21 containing the noise leaked into the low frequency oscillator 21 through the terminals 17 and 20 using the band pass filter 22, the detector 23
The voltage is detected by the voltage comparator 24, and the synchronous/asynchronous determination is made by the voltage comparator 24. The output of the low frequency oscillator 25 is opened and closed by a switch 26 according to the synchronization judgment output, and then counted by a counter 27, converted into a digital parallel signal, and then inputted to a digital-to-analog converter 28, where it is converted into an analog signal. Ru. Since the switch 11 is controlled to be closed during synchronization and open during non-synchronization, the counter 27 maintains its state during synchronization and counts up during non-synchronization.

As a result, the output of the digital-to-analog converter 28 maintains its state during synchronization, and generates a voltage that is microscopically step-like and macroscopically sawtooth during non-synchronization. This voltage is output from the terminal 29, inputted into the phase-locked loop via the terminal 18 connected to the human power of the synthesizer 13, superimposed on the control signal of the loop, passed through the low-pass filter 14, and is input to the voltage-controlled oscillator 15.
to control the sweep.

FIG. 2 is a block configuration diagram showing the configuration of a second embodiment of the present invention. Low pass filter 14 compared to the first embodiment
The configuration is the same except that the connection order between the two and the synthesizer 13 is reversed. Further, the digital sweep circuit 2 has the same configuration as that shown in FIG. Further, the operation of this embodiment is similar to that of the first embodiment.

〔Effect of the invention〕

As explained above, the present invention provides a bandpass filter in the synchronization determination circuit of the sweep circuit of the phase-locked loop, so that stable synchronization and asynchronous determination can be performed even when a signal with a low S/N ratio is input, and a wide synchronization range is ensured. There is an effect that can be done.

23...Detector, 24...Voltage comparator, 26...
Switch, 27...Counter, 28...Digital-analog converter.

Claims (1)

[Claims] 1. A phase comparator (11) into which a phase modulated wave signal arrives; a voltage controlled oscillator (15) that supplies a recovered carrier signal to this phase comparator; and a signal generated by the phase comparator. a carrier wave reproduction signal processing circuit (12) that generates a phase difference signal corresponding to the phase difference between the phase modulated wave signal and the reproduced carrier wave signal based on the phase difference signal; an oscillator (21) that oscillates in response to this phase difference signal; synchronization determination means (23,
24), synchronization control signal generation means (25 to 28) that generates a synchronization control signal based on the determination result of the synchronization determination means, and a signal related to a signal obtained by combining the synchronization control signal and a signal related to the phase difference signal. A phase synchronization demodulator is provided with a synthesizer (13) that provides a synthesizer (13) to the voltage controlled oscillator. A phase-locked demodulator comprising: a filter (22).