JPH08265385A - Doubly modulated signal demodulation circuit - Google Patents

Abstract

PURPOSE: To prevent the transmission of the service channel(SC) signal in a noise state at not only the time of the step-out of a reproduction carrier wave but also the time of the input disconnection of a doubly modulated signal. CONSTITUTION: An automatic gain control amplifier circuit 1 performs AGC amplification for the doubly modulated signal a of a main signal and an SC signal and outputs a control signal f when the disconnection of a doubly modulated signal b is detected. A phase detector 2 performing a phase detection for the signal b, an identification device 3 for main signal d identification and reproduction, an APC(automatic phase control) detection circuit 4 for generating a VCO(voltage controlled oscillator) control signal f and a VCO 5 for generating a reproduction carrier wave g compose a carrier wave reproduction loop. When a carrier wave asynchronization detection circuit 6 detects the asynchronization of the reproduction wave g from the VCO control signal f, the circuit 6 generates a step-out signal i. An SC signal reproduction circuit 7 reproduces an SC signal h from the VCO control signal f but when the circuit 7 receives a control signal j or the step-out signal i, the circuit stops the transmission of the SC signal h.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a carrier wave as a main signal for n (n
Is an integer greater than or equal to 2) PSK (Phase Shift Keying) signal or n-value QAM (Quadrature Amplitude Modulation) signal is modulated into a multi-level digital modulation signal including a phase modulation term, and this multi-level digital modulation signal is serviced. The present invention relates to a dual modulation signal demodulation circuit that reproduces the main signal and the SC signal from a double modulation signal that is further frequency-modulated with a channel signal (hereinafter, SC signal), and particularly includes a carrier wave asynchronous detection circuit that detects the asynchronous of the reproduced carrier wave. The present invention relates to a dual modulation signal demodulation circuit.

[0002]

2. Description of the Related Art One of conventional double-modulation signal demodulation circuits of this type is disclosed in Japanese Patent Laid-Open No. 64-36249.
Carrier wave synchronization circuit). This dual modulation signal demodulation circuit is basically a VCO that generates a reproduced carrier wave in response to a VCO control signal, and a phase detection that phase-detects the dual modulated signal with the reproduced carrier wave as a reference to generate a baseband signal. And a discriminator for discriminating and reproducing the baseband signal to generate a demodulation main signal and discriminating phase information contained in the baseband signal for each predetermined modulation phase to generate a phase information signal, and the phase From the VCO control signal, an APC detection circuit and a loop filter that generate a VCO control signal that eliminates the phase difference between the carrier wave of the double modulated signal and the reproduced carrier wave in response to the information signal. An SC signal reproduction circuit for reproducing and outputting the SC signal, and synchronization of the reproduced carrier wave with the carrier wave in response to the operation output of the APC signal detection circuit. A carrier asynchronous detecting circuit for detecting a deviation (asynchronous),
And an SC signal output control circuit for stopping the output of the SC signal when receiving the out-of-synchronization signal from the carrier wave asynchronous detection circuit.

Therefore, this dual modulation signal demodulation circuit prevents the disturbed SC signal and noise from being output from the SC signal reproduction circuit even if the reproduced carrier wave is out of synchronization. There is a feature that it is possible to prevent malfunction of a device that operates by receiving the SC signal from the device, for example, a communication control device such as a line switching device or a monitoring system.

[0004]

In the above-mentioned dual modulation signal demodulation circuit, the reproduced carrier wave naturally changes from the synchronous state to the asynchronous state even when the dual modulation signal is not supplied to the phase detector. At this time, before the carrier wave asynchronous detection circuit detects the asynchronous of the reproduced carrier wave, the operation output from the APC detection circuit becomes a noise state and is input to the SC signal reproduction circuit. Outputs noise. Therefore, even if a means for detecting the asynchronous of the reproduced carrier wave and stopping the output of the SC signal reproducing circuit is provided,
There is a drawback in that a device used for controlling the SC signal may malfunction.

[0005]

A dual modulation signal demodulation circuit of the present invention modulates a carrier wave into a multilevel digital modulation signal containing a phase modulation term with a main signal and then uses this multilevel digital modulation signal as a service channel signal. Further, an automatic gain control amplifier circuit for automatically amplifying the frequency-modulated double modulation signal to a constant amplitude, a VCO for generating a reproduced carrier wave in response to the VCO control signal, and the double modulated signal having a constant amplitude for the reproduced carrier wave A phase detector that detects the phase of the baseband signal based on the above, and a phase demodulation signal that identifies and reproduces the baseband signal to generate a demodulation main signal and corresponds the phase information included in the baseband signal to the phase modulation term. A discriminator that discriminates each phase to generate a phase information signal, and performs a predetermined operation in response to the phase information signal to perform a predetermined operation on the carrier wave of the dual modulation signal An APC signal detection circuit that generates the VCO control signal that eliminates the phase difference from the carrier wave, an SC signal reproduction circuit that reproduces the service channel signal from the VCO control signal, and the reproduction in response to the VCO control signal. A carrier asynchronous detection circuit for detecting the asynchronism of the carrier with respect to the carrier, and the SC signal when the dual modulation signal is not supplied to the phase detector and when the carrier asynchronous detector detects the asynchronous of the reproduced carrier. And an SC signal output stop circuit for stopping the output of the service channel signal from the reproduction circuit.

In the dual modulation signal demodulation circuit, when the SC signal output stop circuit has the automatic gain control voltage of the automatic gain control amplifier substantially equal to the maximum voltage, the dual modulation to the phase detector is performed. A configuration can be adopted in which it is determined that no signal is supplied.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment according to the present invention.

In this dual modulation signal demodulation circuit, an automatic gain control (AGC) amplification circuit 1 is supplied with a dual modulation signal a whose carrier is an intermediate frequency band signal. The dual modulation signal a is
The carrier wave is a main signal which is a digital signal and is modulated into a multi-level digital modulation signal including a phase modulation term such as an n-level PSK signal or an n-level QAM signal, and this multi-level digital modulation signal is further converted into an SC signal such as an analog signal. It is a frequency-modulated signal. The AGC amplifier circuit 1 amplifies this double modulation signal a by automatic gain control (AGC) to generate a double modulation signal b having a constant amplitude. Here, the AGC amplifier circuit 1 controls the output level of the double modulation signal b by the AGC voltage, and when the supply of the double modulation signal a is stopped, this AGC voltage becomes almost the maximum voltage. When the AGC amplifier circuit 1 detects the almost maximum AGC voltage, it sends the control signal j to the SC signal reproduction circuit 7.

The double modulated signal b is supplied to the phase detector 2. The phase detector 2 phase-detects the double modulation signal b with the reproduced carrier wave g from the VCO 5 as a reference, and generates a baseband signal c. The baseband signal c is sent to the discriminator 3. The discriminator 3 discriminates and reproduces the main signal included in the baseband signal c, and further performs A / A for the reproduced main signal.
Demodulated main signal d encoded by performing signal processing such as D conversion
Is output. The discriminator 3 also discriminates the baseband signal c for each predetermined modulation phase, and produces the phase information signal e discriminated for each modulation phase. The phase information signal e contains information about the SC signal.

The phase information signal e is an APC (Automat).
ic Phase Control) detection circuit 4. The APC circuit 4 responds to the phase information signal e to perform a predetermined operation according to a well-known technique so as to bring the phase difference between the carrier wave of the double modulation signal b and the reproduced carrier wave g close to zero.
The control signal f is supplied to the VCO 5. VCO5 is this VC
A reproduced carrier wave g is generated in response to the O control signal f. As described above, the phase detector 2, the discriminator 3, and the APC detection circuit 4
And VCO 5 form a carrier recovery loop for demodulating a digital phase modulation signal, which is conventionally known.

The VCO control signal f is also supplied to the carrier wave asynchronous detection circuit 6 and the SC signal reproduction circuit 7. The carrier wave asynchronous detection circuit 6 is a circuit using a well-known technique, and has a VC
In response to the O control signal f, the double modulation signal b of the reproduced carrier wave g
Of the carrier wave of the
Is generated.

When the reproduced carrier wave g is in the synchronous state, the SC signal reproducing circuit 7 receives the normal S signal from the VCO control signal f.
Reproduce the C signal h. That is, since the VCO control signal f corresponds to the SC signal, the SC signal reproduction circuit 7 outputs the signal f
Is amplified to a predetermined level, and the SC signal h is reproduced. Further, the SC signal reproduction circuit 7 outputs the out-of-synchronization signal i or A from the carrier asynchronous detection circuit 6.
When the control signal j from the GC amplifier circuit 1 is received, the output of the SC signal h is stopped by the operation of the switch circuit or the like SC
A signal output stop circuit is further provided. That is, this S
In the C signal output stop circuit, the dual modulation signal b is applied to the phase detector 2
If the carrier wave asynchronization detection circuit 6 detects that the reproduced carrier wave g is not synchronized, the output of the SC signal h from the SC signal reproduction circuit 7 is stopped.

The operation of stopping the SC signal output of the SC signal reproducing circuit 7 will be described in more detail. When the double modulation signal a is no longer supplied, the double modulation signal b from the AGC amplifier circuit 1 disappears first. When the double modulation signal b disappears, the AGC amplifier circuit 1 sends the control signal j to the SC signal reproduction circuit 7. When the double modulation signal b disappears, the phase detector 2 stops outputting the baseband signal c, and the phase information signal e output from the discriminator 3 has an uncertain value. Therefore, the VCO control signal f output from the APC detection circuit 4 becomes asynchronous, and this asynchronous VCO control signal f is generated by the carrier wave asynchronous detection circuit 6 and the SC signal reproduction circuit 7.
Is supplied to.

According to the above operation, the out-of-synchronization signal i is output from the carrier asynchronous detection circuit 6 and the SC signal h is output from the SC signal reproduction circuit 7 at substantially the same time, but the double modulation signal is output. The time until the supply of a to the AGC amplifier circuit 1 is detected is longer than that when the carrier wave asynchronous detection circuit 6 detects that the reproduced carrier wave g is asynchronous, the phase detector 2, the discriminator 3, and the APC. Detection circuit 4
It is earlier by the delay time that occurs in. Therefore, when the transmission of the SC signal h is stopped by the control signal j output from the AGC amplifier circuit 1, the SC in the noise state is stopped by the out-of-synchronization signal i generated by the VCO control signal f in the noise state. It is possible to reliably prevent the transmission of the signal h.

[0015]

As described above, according to the present invention, when the dual modulation signal of the main signal and the service channel signal is not supplied to the phase detector, and when the carrier asynchronous detection circuit detects the asynchronous of the reproduced carrier. Since the SC signal output stop circuit that stops the output of the reproduced service channel signal from the SC signal reproduction circuit is provided, the reproduction service in the noise state is not only caused when the reproduced carrier wave is asynchronous, but also when the supply of the double modulation signal is stopped. This has the effect of preventing the transmission of channel signals. Therefore, there is an effect that it is possible to prevent a malfunction of a device which operates by receiving the service channel signal from the SC signal reproducing circuit of the present invention, for example, a communication control device such as a line switching device or a monitoring system.

[Brief description of drawings]

FIG. 1 is a block diagram of a dual modulation signal demodulation circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 Automatic Gain Control Amplifier Circuit 2 Phase Detector 3 Discriminator 4 VCO 5 APC Detection Circuit 6 Carrier Asynchronous Detection Circuit 7 SC Signal Regeneration Circuit

Claims (2)

[Claims] 1. A dual modulation signal obtained by modulating a carrier wave into a multilevel digital modulation signal including a phase modulation term with a main signal and further frequency-modulating the multilevel digital modulation signal with a service channel signal, and automatically controlling the gain to a constant amplitude. An automatic gain control amplifier circuit for amplifying, a VCO for generating a reproduced carrier wave in response to a VCO control signal, and a phase detector for phase-detecting the double modulated signal having a constant amplitude with reference to the reproduced carrier wave to generate a baseband signal. And a discriminator that discriminates and reproduces the baseband signal to generate a demodulation main signal and discriminates phase information included in the baseband signal for each phase corresponding to the phase modulation term to generate a phase information signal. , The VCO control signal for performing a predetermined calculation in response to the phase information signal to eliminate the phase difference between the carrier wave of the dual modulation signal and the reproduced carrier wave. APC signal detecting circuit for generating a signal, an SC signal reproducing circuit for reproducing the service channel signal from the VCO control signal, and a carrier wave asynchronous detection for detecting an asynchronism of the reproduced carrier wave with respect to the carrier wave in response to the VCO control signal. Circuit, and when the dual modulation signal is not supplied to the phase detector and when the carrier wave asynchronous detection circuit detects the asynchronous of the reproduced carrier wave, the output of the service channel signal from the SC signal reproduction circuit is stopped. A dual modulation signal demodulation circuit, comprising: an SC signal output stop circuit. 2. The SC signal output stop circuit determines that the double modulation signal is not supplied to the phase detector when the automatic gain control voltage of the automatic gain control amplifier is almost the maximum voltage. The dual modulation signal demodulation circuit according to claim 1, wherein