JPH05244212A - Demodulator - Google Patents

Abstract

PURPOSE:To build up an inexpensive system without needing the frequency stability of a local oscillator of a transmission side by obtaining a demodulator with a wide input frequency fluctuation range without causing fixed deterioration in a bit error. CONSTITUTION:A frequency divider converter 2 mixes an input signal from a signal input terminal 1 and a local oscillation signal from a local oscillator 3 to produce an intermediate frequency signal. A digital demodulator 2 includes a carrier recovery circuit recovering the carrier of the intermediate frequency signal, in which a multiplier 4 applies synchronization detection based on the recovery carrier. When the frequency of the recovered carrier from a VCO 5 is deviated from a predetermined permissible range, a control circuit 13 controls the frequency of the local oscillation signal generated from the local oscillator 3 so as to restore the recovered carrier frequency into the permissible range in response to the output of the carrier synchronization detector 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator provided in a receiver of a microwave digital communication device.

[0002]

2. Description of the Related Art Conventionally, a demodulator of this type has a carrier reproducing circuit in a digital demodulator, and controls the frequency of the reproduced carrier to detect the carrier component of the demodulated main signal in synchronization with it. The frequency of the demodulated main signal was not controlled.

A conventional demodulator will be described below with reference to the block diagram of FIG. The carrier wave signal input to the signal input terminal 1 of this demodulator is mixed with the local oscillation signal of the fixed frequency from the local oscillator 3A by the frequency converter 2, converted into the intermediate frequency signal, and then the digital demodulator 12
Sent to A. Then, the carrier of the intermediate frequency signal is reproduced in the demodulator 12A by the carrier synchronization detection circuit 6 and the VCO 5, and the reproduced carrier and the carrier component of the intermediate frequency signal (demodulation main signal) are synchronized and detected by the multiplier 4. It was

[0004]

However, in the above demodulator, in order to increase the reproduction carrier synchronization range, it is necessary to widen the carrier reproduction loop band of the digital demodulator, which in turn increases the jitter. However, there is a drawback that fixed deterioration of bit error characteristics increases. Therefore,
If the transmission capacity becomes smaller (the band of the intermediate frequency signal becomes narrower), the fixed deterioration becomes non-negligible, and it becomes necessary to narrow the carrier synchronization range. Therefore, the transmitter local oscillator of the transmitter side device and this demodulator The frequency stability of the local oscillator and the like has to be increased, which has a drawback of increasing the cost of the communication device.

[0005]

A demodulator according to the present invention comprises a frequency converter for mixing an input signal and a local oscillation signal to generate an intermediate frequency signal, and supplying the local oscillation signal to the frequency converter. A local oscillator capable of controlling the frequency of a local oscillation signal, a digital demodulator including a carrier regeneration circuit for performing carrier regeneration of the intermediate frequency signal, for performing synchronous detection of the intermediate frequency signal with the regeneration carrier as a reference, and the carrier regeneration In response to the reproduction carrier frequency control signal from the circuit, when the frequency of the reproduction carrier deviates from the predetermined allowable range, the frequency of the local oscillation signal is adjusted so that the reproduction carrier frequency is returned to the allowable range. And a control circuit for controlling.

[0006]

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

The signal input from the signal input terminal 1 of this demodulator is mixed with the local oscillation signal output from the local oscillator 3 by the frequency converter 2, the unnecessary wave is removed, and the intermediate frequency signal is converted. Multiplier 4 in digital demodulator 12
Is supplied to one input terminal of. On the other hand, the regenerated carrier generated by the VCO 5 is supplied to another input terminal of the multiplier 4.
The intermediate frequency signal (demodulation main signal) mixed with the reproduced carrier in the multiplier 4 is synchronously detected and taken out as a baseband signal, and is output from the signal output terminal 7 through the carrier synchronization detector 6.

The carrier synchronization detector 6 determines whether the phase of the reproduced carrier is behind or ahead of the phase of the intermediate frequency signal, and the VCO 5 is set so that the reproduced carrier phase becomes the optimum phase through its own loop filter.
The frequency of the reproduction carrier generated by is controlled. This control voltage output from the carrier synchronization detector 6 to the VCO 5 is branched into two before entering the VCO 5, and is further branched into 2 when input into the control circuit 13 and supplied to the comparators 8 and 9. The comparator 8 compares the control voltage with the upper limit value of the reference voltage generated in the reference voltage setting unit 10, and amplifies the deviation when the control voltage exceeds the upper limit value of the reference voltage, so that the deviation is 0 or The frequency of the local oscillation signal output by the local oscillator 3 is controlled so as to have the opposite polarity. On the other hand, the comparator 9 compares the input control voltage with the lower limit value of the reference voltage generated in the reference voltage setting device 11, and when the control voltage is below the lower limit value of the description voltage, the local oscillation signal of Control the frequency.

Frequency converter 2, demodulator 12, control circuit 1
3 and the local oscillator 3 are closed, there is a constant relationship between the carrier frequency of the intermediate frequency signal input to the demodulator 12 and the control voltage to the VCO 5. If the frequency of the local oscillation signal generated by the local oscillator 3 is controlled so as to keep it constant,
The carrier frequency of the intermediate frequency signal input to the demodulator 12 is kept constant. That is, even if the frequency of the input signal changes, the frequency of the input signal (intermediate frequency signal) to the demodulator 12 is controlled and kept constant, so that a demodulator having a wide allowable range of input frequency fluctuation can be configured.

[0010]

As described above, according to the present invention, by providing the frequency converter, the local oscillator and the control circuit in addition to the demodulator, the change in the input frequency of the demodulator can be made small, so that regardless of the transmission capacity. It is possible to provide a demodulator with a wide allowable range of input frequency fluctuations without causing fixed deterioration of bit errors. Therefore, it is not necessary to increase the frequency stability of the transmitter local oscillator and the receiver local oscillator, and an inexpensive system can be constructed.

[Brief description of drawings]

FIG. 1 is a block diagram of a demodulator showing an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional demodulation device.

[Explanation of symbols]

 1 signal input terminal 2 frequency converter 3, 3A local oscillator 4 multiplier 5 VCO 6 carrier synchronization detector 7 demodulation output terminal 8, 9 comparator 10 reference voltage setter 11 reference voltage setter 12, 12A digital demodulator 13 control circuit

Claims (2)

[Claims] 1. A frequency converter for generating an intermediate frequency signal by mixing an input signal and a local oscillation signal, and a local oscillator capable of controlling the frequency of the local oscillation signal for supplying the local oscillation signal to the frequency converter. A digital demodulator that includes a carrier reproduction circuit that reproduces the carrier of the intermediate frequency signal and performs synchronous detection of the intermediate frequency signal with the reproduced carrier as a reference; and a response to a reproduced carrier frequency control signal from the carrier reproduction circuit. And a control circuit for controlling the frequency of the local oscillation signal so that the reproduction carrier frequency is returned to the allowable range when the frequency of the reproduced carrier deviates from a predetermined allowable range. Demodulator. 2. The control circuit compares the reproduction carrier frequency control signal with a reference voltage having a constant voltage range, and when the reproduction carrier frequency control signal is out of the constant voltage range of the reference voltage. 2. The frequency of the local oscillation signal is controlled so that the reproduction carrier control signal returns to within a certain range of the reference voltage.
The demodulator described.