JPS62139448A - Carrier recovery circuit - Google Patents

Abstract

PURPOSE:To prevent the titled circuit from disabling reception due to pseudo pull-in and to improve the reliability of a receiving device by starting/stopping a sweeper on the basis of a failure detecting signal detected by an error ratio of a demodulating signal. CONSTITUTION:The phase of an input signal is detected by a phase detecting means 101, identified by a identifier 103 and coded by a code conversion means 104 on the basis of differential logic. A code error ratio is detected by an error detecting means 105 and divided with frequency by a failure detecting means 106, and when the frequency-divided value exceeds a specified value, a failure detecting signal is generated and the oscillation frequency is sweeped to a range wider than a pull-in range by the sweeper 102.

Description

[Detailed Description of the Invention] [Shelf] A carrier wave regeneration circuit that includes a phase-locked loop and controls a voltage controlled oscillator based on a phase difference signal between an input signal and a regenerated carrier wave signal to regenerate a carrier wave is free from synchronization loss. When a fault occurs, a signal is generated to detect the fault state based on the error rate in the demodulated signal obtained by code processing the output of the signal identified by phase detection of the input signal using the regenerated carrier signal, and this signal is used to detect the fault state. The sweeper is operated to perform forced synchronization pull-in in the phase-locked loop, and the sweeper is stopped when synchronization is established and no fault detection signal is generated, so the input signal consisting of an n-phase phase-shifted open wave and the clock signal Pseudo-entrainment does not occur at frequencies that differ by an integral multiple of 1/n.

[Industrial application field]

The present invention relates to a carrier wave recirculation circuit for demodulating received signals on the receiving side of a digital communication device, and more particularly to a carrier wave regeneration circuit that prevents false pull-in when performing synchronization pull-in using an out-of-synchronization sweeper.

A demodulator that demodulates a phase modulated signal has a carrier regeneration circuit that regenerates a carrier wave from a received signal, and uses this regenerated carrier wave to perform phase detection on the received signal to extract a modulated baseband signal. l! It transmission wave regeneration circuit is usually configured with a phase-locked loop (PLL), but in this PLL circuit, in addition to the carrier wave frequency (fo), the clock frequency (fc) in the modulated baseband signal
Frequencies separated by an integral multiple of 17n (n is the number of phases of phase modulation), that is, fo±fc/n, fo±2f c/n,
・- (hereinafter referred to as pseudo-entrainment frequency), a so-called pseudo-entrainment phenomenon also occurs, but when pseudo-entrainment occurs, demodulation is not performed normally and reception becomes impossible, so carrier wave regeneration that does not cause pseudo-entrainment occurs. circuit is required.

[Conventional technology]

FIG. 3 shows a conventional general transmission regeneration circuit.

In the figure, 1 and 2 are hybrids, 3 and 4 are mixers, and these constitute a phase detector 5. Also 6
is a voltage controlled oscillator (VCO), 7 is a phase comparator, 8 is a low-pass filter, and 9 is a sweeper.

In FIG. 3, the received signal is frequency-converted in a frequency converter (not shown) to generate intermediate frequency signals, which are input to the hybrid 1, branched in phase, and applied to mixers 3 and 4, respectively.

On the other hand, the regenerated carrier wave signal of the VCO 6 is applied to the hybrid 2, branched in the same phase, and applied to mixers 3 and 4, respectively. As a result, mixer 3.4 generates in-phase and quadrature baseband signal outputs as phase detection outputs, which are both input to phase comparator 7.

The phase comparator 7 is composed of, for example, a well-known Costas type baseband processing circuit, and when the input is a four-phase phase modulated wave signal, the phase comparator 7 differentiates one signal generated by multiplying the input by four, and the other signal. By mixing, the DC component and 4
Obtain an output consisting of harmonic components. By removing high frequency components from this output through a low pass filter 8,
A DC output is obtained according to the frequency difference between the input intermediate frequency signal and the reproduced carrier signal.

This DC output is applied to VCO 6 to control the frequency of the regenerated carrier signal it generates, causing it to be drawn into the input signal. At this time, the phase comparator 7 determines whether or not it is in the synchronization pull-in state, and if it is out of synchronization, it issues an alarm signal (C
RALM).

In conventional carrier wave regeneration circuits like this, once synchronization is achieved, the range in which it can follow even if the frequency difference becomes large, that is, the lock range, is relatively wide, but when it loses synchronization, it has to resynchronize. The capture range is usually quite narrow. Therefore, in order to facilitate re-input in the event of line disconnection, etc., a sweeper 9 is provided, and when the synchronization is lost, the CI? It is activated by the ALM signal to control the VCO6, sweeps the VCO oscillation frequency over a range above the normal re-pulling range, and synchronizes. When the synchronous re-pulling state is reached, the sweeper is stopped and the normal We are trying to move to the operation of .

[Problem that the invention seeks to solve]

In the carrier wave regeneration circuit shown in FIG. 3, the carrier wave frequency f
A so-called pseudo-entrainment phenomenon occurs in which synchronization occurs at frequencies other than O groups such as Co±f c /n.

FIG. 4 explains the pseudo pull-in, and in the case of a four-phase phase modulated wave signal, in addition to the carrier wave frequency fo=70MIlz, which is the normal pull-in point, the clock frequency E C=
Frequency 67.5 separated by 1/4 of 10Ml1z above and below
fEt-like entrainment occurs in MIIz and 72.5Ml1z, etc.

Therefore, if synchronization occurs due to line disconnection, etc., and the sweeper operates and a pseudo pull-in occurs at a frequency of 67, 5 Mllz, and the sweeper stops, the phase comparator 7 cannot distinguish it from a synchronous state, CR
No ALM signal is generated.

However, in such a pseudo pull-in state, since the reproduced carrier frequency is not a regular frequency, the code on the transmitting side is not correctly decoded in the baseband signal output of the phase detector 5, resulting in an error state.

For this reason, in the past, an automatic frequency control device (AFC) was further provided to control the VCO oscillation frequency and draw it to the correct carrier frequency.

However, AFC devices are generally expensive and therefore
It is desired to realize a carrier wave regeneration circuit that can prevent pseudo pull-in without using an FC device.

[Means for solving problems]

In order to solve the problems of the prior art, the present invention provides a carrier wave regeneration circuit equipped with a phase-locked loop that performs synchronization using a sweeper when out of synchronization.
It has the basic configuration as shown in the figure.

Reference numeral 101 denotes a phase detection means, which performs phase detection on a polyphase phase modulated wave input signal using the output signal of the voltage controlled oscillator to obtain an output, and is equipped with a phase locked loop to compare the phase of the phase detection output and determine the phase difference between the two signals. This signal is used to control the oscillation frequency of the voltage controlled oscillator and keep it in synchronization.

Reference numeral 102 denotes a sweeper, which is started and stopped by a fault detection signal from the fault detection means 106 when the phase-locked loop is out of synchronization, and sweeps the oscillation frequency of the voltage-controlled oscillator to a frequency range wider than the synchronization pull-in range, thereby performing synchronization pull-in. .

A discriminator 103 discriminates the phase detection output of the phase detection means 101 to obtain a code output.

Reference numeral 104 denotes code converting means, which performs code processing on the code output of the discriminator 103 using differential logic to generate a demodulated signal.

Reference numeral 105 denotes an error rate detection means, which detects the code error rate in the demodulated signal of the code conversion means 104.

106 is a failure detection means, and the error rate detection means 105
When the error rate exceeds a certain value, a fault detection signal is generated.

(Function) When a loss of synchronization occurs in a carrier wave regeneration circuit that is equipped with a phase-locked loop and controls a voltage controlled oscillator based on a phase difference signal between an input signal and a regenerated carrier wave signal to regenerate a carrier wave, the demodulated signal When a signal to detect a fault condition is generated due to the error rate in Therefore, 1/n of the input signal and clock signal
Pseudo pull-in does not occur at a frequency that differs by an integral multiple of , and therefore a situation in which reception becomes impossible due to pseudo pull-in can be avoided.

〔Example〕

FIG. 2 shows one embodiment of the present invention, and FIG.
The same parts as in the figure are indicated by the same numbers, 11 is an identifier, 12 is a reception code conversion board, 13 is a U-8 conversion board,
14 is a parity check circuit, and 15 is a frequency divider.

In FIG. 2, a discriminator 11 identifies the baseband signal generated in the phase detector 5 and performs code recovery. 4
In the case of a phase-modulated wave signal, four detection points are generated every 90'' depending on the phase of the regenerated carrier wave that performs phase detection, and each generates a different code output, but the receiving code conversion board 12 uses the same known signal as on the transmitting side. It has a differential logic of The U-B conversion board converts the unipolar code into a bipolar code and sends it to the transport device (not shown).

The parity check circuit 14 performs a parity check using parity pits inserted in the received code,
Check whether the received code is correctly restored,
Generates an error rate signal. The frequency divider 15 consists of a counter, etc., and divides the error rate signal of the parity check circuit 14, and generates a failure detection signal when the value becomes larger than a certain value. The sweeper 9 is activated by a fault detection signal to start sweeping, and when this signal disappears, the sweep is stopped to perform synchronous pull-in.

That is, in the case of the present invention, the sweeper 9 is not activated by the CRALM signal indicating the loss of synchronization in the phase comparator 7, but is activated or stopped in accordance with the detection of a fault in the reception code converter board 12. Sweeper 9 does not stop even if the pseudo-retraction conditions are met,
Therefore, false entrainment is prevented.

The reason why the frequency divider 15 is provided to divide the error rate signal of the parity check circuit 14 and generate a fault detection signal is because the output of the parity check circuit 14 is used as a fault alarm on the normal line. , is a line switching command, and the parity check output is frequency-divided to delay the activation point of the failure detection signal so that the sweeper of the demodulator in secondary 1 is not activated before the line is switched.

〔Effect of the invention〕

As explained above, according to the carrier wave regeneration circuit of the present invention,
The voltage controlled oscillator is controlled based on the phase difference signal between the input signal and the regenerated carrier signal (starting and stopping of the sweeper, which performs forced synchronization of the phase-locked loop that regenerates the general transmission wave, is controlled based on the error rate of the demodulated signal). Since this is done using the fault detection signal detected by Since pseudo pull-in does not occur at a frequency that is twice as different, it is possible to avoid a situation where reception becomes impossible due to pseudo pull-in, and it is possible to improve the reliability of the receiving device.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is a diagram showing an embodiment of the present invention, Fig. 3 is a diagram showing a conventional carrier wave regeneration circuit, and Fig. 4 is a diagram explaining pseudo pull-in. It is a diagram. 1.2-m-hybrid, 3.4-mixer, 5-phase detector, 6-voltage controlled oscillator (VCO), 7--phase comparator, 8-low-pass filter, 9-sweeper, 11--Discriminator, 12--Receiving code converter board, 13-U-B converter board, ]4-Parity check circuit, 15--Frequency divider phase detector Fig. 6 Diagram showing pseudo pull-in 4 Figure

Claims (1)

[Claims] A multiphase phase modulated wave input signal is phase-detected using an output signal of a voltage controlled oscillator to obtain an output, and the outputs are phase-compared to extract a phase difference signal between the two signals. Phase detection means (10
1), a sweeper (102) that performs synchronization by sweeping the oscillation frequency of the voltage controlled oscillator to a frequency range wider than the synchronization pull-in range when the phase-locked loop is out of synchronization;
a discriminator (1) for discriminating the phase detection output and obtaining a code output;
03), and a code conversion means (which processes the code output using differential logic to reproduce the transmitting side code and generates a demodulated signal).
104), an error rate detection means (105) for detecting a code error rate in the demodulated signal; and dividing the error rate and generating a fault detection signal when the error rate exceeds a certain value. 1. A carrier wave regeneration circuit comprising a fault detection means (106) for starting and stopping the sweeper (102) according to the fault detection signal.