JPH0583310A - Automatic frequency control circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a transmitter-receiver for a pilot signal by providing a carrier recovery circuit and a multiplier for a reference carrier obtained from a 1/N frequency divider circuit with a reception signal to the control circuit. CONSTITUTION:A reception signal is multiplied by a multiple of N at an N multiple circuit 1 and a modulation component is eliminated. A carrier signal subject to N multiple is given to a phase comparator 3 in which the signal is compared with an output signal of a voltage controlled oscillator(VCO), an output detecting a phase difference is used to control the VCO 2 through a loop filter 4. Then the phase locked loop comprising the phase comparator 3, the loop filter 4 and the VCO 2 follows the carrier component of N multiple and recovers the carrier signal of the frequency component being a multiple of N of a reception signal. The carrier is subject to 1/N frequency division by a 1/N frequency divider circuit 5 to obtain a carrier in matching with the phase of the original reception signal. Then the carrier signal and the reception signal are multiplied by a multiplier 6 and a correct base band signal is obtained from a demodulator 7. Thus, a transmitter-receiver for a pilot signal having been used conventionally for frequency correction is not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic frequency control circuit, and more particularly to an automatic frequency control circuit used in a receiver for digital satellite communication.

[0002]

2. Description of the Related Art In a conventional automatic frequency control (hereinafter referred to as AFC) circuit, as shown in FIG. 2, a pilot signal sent at the same time as a modulated signal as a received signal is multiplied by a multiplier 2
2 and a voltage controlled oscillator (hereinafter referred to as VCO) 21 to demodulate, compare with a local oscillation signal that serves as a reference of a pilot signal, control the VCO 21 to cancel the difference, and correct the frequency of the original baseband signal. Was there. The conventional AFC circuit shown in FIG. 2 has a voltage-controlled oscillator (VCO) 21 whose oscillation frequency changes according to a control voltage, a received signal and a VCO.
A multiplier 22 that multiplies the output of CO, a bandpass filter 23 that passes the frequency of a pilot signal, a local oscillator 24 that serves as a reference for a pilot signal on the receiving side, and a phase comparison that compares the pilot signal with a reference local oscillation signal. Bowl 25
And the output of the phase comparator 25 is filtered to
It is composed of a loop filter 26 for adjusting the feedback phase to 21. Therefore, the transmitting side transmits the pilot signal at the same time as the modulated signal, the receiving side receives the modulated signal and the pilot signal, and the pilot signal is equivalent to the reference local oscillation signal and the phase comparator 25 which are equivalent to the pilot signal output from the local oscillator 24. Then, the VCO 21 is controlled so as to cancel the difference and the frequency of the received signal is corrected. Since the baseband signal of the received signal converts the frequency of the baseband signal by the output of the controlled VCO 21, the frequency of the baseband signal is similarly corrected and the demodulator 28 is compensated for the frequency deviation, and the baseband on the sending side is compensated. Had been taken out.

[0003]

The conventional AFC circuit requires a device for transmitting and receiving a pilot signal for frequency correction in addition to the modulation signal. Therefore, even if a single satellite repeater has a small number of lines, it is necessary to equip the transmitter and receiver with a pilot signal device. It had the drawback of being less efficient.

[0004]

SUMMARY OF THE INVENTION An automatic frequency control circuit of the present invention comprises an N multiplication circuit for multiplying a received signal such as a PSK modulated signal by N, and an output frequency of the N (N is an integer of 2 or more) multiplication circuit. A voltage controlled oscillator that generates equal signals, a phase comparator that compares the output signal of the N multiplication circuit and the output signal of the voltage controlled oscillator, and an unnecessary component that is output from the phase comparator to remove the unnecessary voltage. A loop filter for supplying a phase control voltage to a controlled oscillator, an N divider for dividing an output signal of the voltage controlled oscillator by N, and a multiplier for multiplying the received signal by an output signal of the N divider. , And a demodulator that demodulates the modulated signal output from this multiplier.

[0005]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. Figure 1
In this embodiment, an N multiplication circuit 1 that multiplies a received signal by N, a voltage controlled oscillator (VCO) 2 that generates a signal whose output frequency is changed by a control voltage and is approximately equal to the frequency of the N multiplied reception signal, Output signal of N multiplication circuit 1 and VCO2
And a phase comparator 3 for comparing the output signal of
A loop filter 4 that removes unnecessary components output from the VCO 2 and outputs a control voltage that matches the loop phase to the VCO 2, and an N divider circuit 5 that divides the output signal of the VCO 2 by N
A multiplier 6 that multiplies the received signal by a signal obtained by dividing the output of the VCO 2 by N, and a demodulator 7 that multiplies the received signal input to the multiplier 6 by the output signal of the N divider circuit 5 and demodulates. Composed of.

Next, the operation of this embodiment will be described. The received signal is multiplied by N to remove the modulation component. For example, in the case of a two-phase PSK reception signal, if it is multiplied by 2, an unmodulated carrier component that is twice the reception frequency is obtained. The carrier wave signal multiplied by N is compared with the output signal of the VCO 2 by the phase comparator 3, and the output whose phase difference is detected controls the VCO 2 through the loop filter 4. The phase-locked loop formed by the phase comparator 3, the loop filter 4, and the VCO 2 follows the N-fold carrier component and reproduces the carrier signal of the frequency component N times the received signal. By dividing the reproduced carrier wave by N by the N frequency divider circuit 5, a carrier wave having a phase corresponding to the original received signal can be obtained. When this carrier signal is multiplied by the received signal, the output of the demodulator 7 is demodulated by the frequency-corrected carrier signal, so that a correct baseband signal can be obtained.

[0007]

As described above, according to the present invention, the received signal is multiplied by N, and the reference carrier and the received signal obtained from the carrier recovery circuit, which is the frequency component of N times by the phase locked loop, and the N divider circuit. By including a multiplier with
This has the effect of eliminating the need for a transmitter / receiver for pilot signals for frequency correction as in the conventional example.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a conventional AFC circuit.

[Explanation of Codes] 1 N multiplier circuit 2,21 Voltage controlled oscillator (VCO) 3,25 Phase comparator 4,26 Loop filter 5 N divider circuit 6,22 Multiplier 7,28 Demodulator 23,27 Bandpass Filter 24 Local oscillator

Claims (2)

[Claims] 1. An N multiplier circuit for multiplying a received signal such as a PSK modulated signal by N, a voltage controlled oscillator for generating a signal equal to the output frequency of the N (N is an integer of 2 or more) multiplier circuit, and the N multiplier circuit. A phase comparator that compares the output signal of the circuit and the output signal of the voltage controlled oscillator, a loop filter that removes unnecessary components output from the phase comparator and supplies a phase control voltage to the voltage controlled oscillator, An N divider for dividing the output signal of the voltage controlled oscillator by N, a multiplier for multiplying the received signal by the output signal of the N divider, and a demodulator for demodulating the modulated signal output by the multiplier And an automatic frequency control circuit. 2. The PSK modulation signal, which is the received signal, is multiplied by N in the N multiplication circuit, so that the modulation signal component included in the received signal is removed. Item 1. The automatic frequency control circuit according to item 1.