JPS6346810A - Automatic frequency control equipment - Google Patents

Abstract

PURPOSE:To attain stable automatic frequency control even with a low input signal versus noise ratio by stepping-down an output signal of a voltage controlled oscillator including a pilot signal and a phase error signal and applying frequency phase comparison between the result and an output of a step-down reference frequency oscillator. CONSTITUTION:A reception signal from an input terminal 1 is subject to frequency conversion 3, the result is mixed with an output signal of a local oscillator 4 and the frequency conversion output is led to an output terminal 2. Then the pilot signal in the output signal is extracted from a BPF 11 and fed to a phase detector 13 together with an output signal of a voltage controlled oscillator 22. The phase error signal of the detector 13 is fed to the voltage controlled oscillator 22 and made coincident with the pilot signal by a phase locked loop. Then the output signal of the oscillator 22 is divided (23) to step-down (1/N) the frequency of the input signal, the result is fed to a 1/N frequency generator 12 and a frequency comparator 24, where the frequency and phase are compared. With the value N being large, the output signal of the divider 23 is operated stably even to the modulated pilot signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic frequency controller, and in particular, in satellite communication, the d'irot signal emitted from the transmitting side is detected on the receiving side via the satellite, and the pilot The present invention relates to an automatic frequency controller that eliminates frequency fluctuations caused by intra-satellite repeaters and satellite tonnage by matching the signal frequency with the frequency emitted by the transmitting side.

[Conventional technology] In satellite communications, the first-order method is used to eliminate frequency fluctuations that occur within the satellite repeater and Doppler frequency fluctuations that occur due to fluctuations in the relative position of the satellite and the earth. control. In other words, the transmitting station sends out a pilot signal with good frequency accuracy, this ♀gilot signal is received by the receiving station via the satellite, and the ♀gilot signal frequency matches the pilot frequency sent out by the transmitting station. control so that This is called automatic frequency control (AFC).

Conventional automatic frequency control is shown in Figure 2.

The received signal supplied to the signal input terminal 1 is transferred to the frequency converter 3.
The frequency-converted signal is mixed with the output signal of the second local oscillator 4 and supplied to the signal output terminal 2. To explain in detail, the 2-Irosoto signal in the output signal of the 1-frequency converter 3 is extracted by the bandpass filter 11, and the 2-Irosoto signal is extracted from the output signal of the 1-frequency converter 3, and is then output to the reference frequency generator 12.
is supplied to the first phase detector 13 together with the output signal of. The phase error signal of the first phase detector 13 is supplied to the frequency control terminal of the local oscillator 4 via the first loop filter 20 and the voltage adder 19, and the output signal supplied to the signal output terminal 2 is Frequency negative feedback control is performed so that the frequency becomes the same as the output frequency of the reference frequency generator 12. On the other hand, when the frequency fluctuation of the pilot signal is larger than the bandwidth of the bandpass filter 11, initial compensation is performed.

The output signal of the rectangular wave oscillator 16, which is supplied to the integrator 18 via the switch 17, is applied to the voltage adder 19.

The output frequency of the local oscillator 4 is swept at a low speed with a symmetrical triangular wave. This sweep is performed by the bandpass filter 11
The output signal is supplied to the second phase detector 15 together with the output signal of the reference frequency generator 12 via the 900 phase shifter 14, and it is determined whether automatic frequency control is established or not.

When it is detected that automatic frequency control has been established.

A switch 17 is controlled by the output of the second phase detector 15 to cut off the output signal of the rectangular wave generator 16 that is supplied to the integrator 18, thereby stopping the sysweep.

Conventional automatic frequency controllers perform two-phase frequency control by appropriately selecting the loop bandwidth of the roots.

It offers excellent automatic frequency control capabilities that operate down to very low input carrier-to-noise ratios.

[Problem that the invention seeks to solve]

Incidentally, in recent years, it has become common to perform frequency modulation on pilot signals using line control or line monitoring signals. However, when a modulated wave is used as a pilot signal, the carrier wave component may disappear if the degree of modulation is deep, and when using a conventional automatic frequency controller, it is difficult to perform automatic frequency control on the carrier wave. This will result in

It is an object of the present invention to provide an automatic frequency controller for a modulated pilot signal that is stable even at low input signal-to-noise ratios.

[Means for solving problems]

The present invention relates to a circuit that mixes an input signal with a local oscillation signal in a frequency converter to convert the frequency.

The pilot signal in the output signal of the frequency converter is passed through a bandpass filter together with the output signal of the voltage controlled oscillator.
The frequency of the voltage controlled oscillator is set as a pilot signal by feeding a phase error signal from the first phase detector to the voltage controlled oscillator through a first loop filter. a circuit for frequency-downsetting the output signal of the voltage controlled oscillator using a step down converter, and supplying the output signal of the reference frequency generator to a frequency phase comparator together with the output signal of the reference frequency generator;
A circuit that negatively feeds back the error signal of the frequency phase comparator to the frequency control terminal of the local oscillator via a second loop filter and a voltage adder, and a signal band-limited by the bandpass filter to a 9σ phase. an integrator by supplying the signal passed through the shifter and the output signal of the voltage controlled oscillator to a second phase detector and controlling a switch according to the phase error signal of the second phase detector. and a circuit for controlling the supply of a rectangular wave oscillator output signal to the local oscillator, such that during initial compensation, the symmetrical triangular wave output from the integrator is supplied to the frequency control terminal of the local oscillator via the voltage adder. It consists of

Embodiment An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, the automatic frequency controller according to the present invention guides the received signal supplied to the signal input terminal 1 to the frequency converter 3, mixes it with the output signal of the local oscillator 4, and outputs the frequency-converted signal. Supply to terminal 2. To be more specific,
The pilot signal in the output signal is extracted by the bandpass filter 11 and is supplied to the first phase detector 13 together with the output signal of the voltage controlled oscillator 22 . The phase error signal of the first phase detector 13 is supplied to the voltage controlled oscillator 22 through the first loop filter 20, and the output signal frequency of the voltage controlled oscillator 22 is made to match the sipilot signal by the phase locked loop. The output signal of the voltage controlled oscillator 22 has a signal-to-noise ratio equal to the ratio of the loop bandwidth of the phase-locked loop to the bandwidth of the bandpass filter 11. This will improve the pilot signal.

Next, the output signal of the voltage controlled oscillator 22 is supplied to a step down converter 23 to step down the frequency of the input signal by N (N is a positive integer). It is supplied to the frequency phase comparator 24 at the same time as the output signal of the reference frequency generator 12 which outputs a frequency 1/'N lower than that of the reference frequency generator 12. The output error signal of the frequency phase comparator 24 is sent to the local oscillator 4 via the second loop filter 25 and the voltage adder 19.
is supplied to the frequency control terminal of the automatic frequency control loop. By stepping down the output signal of the voltage controlled oscillator 22 by N, the frequency modulation degree of the output signal of the downshifter 23 is 1H compared to the frequency modulation degree of the input pilot signal, and the larger N is, the more The output signal of the down converter 23 can now be considered to be the same as an unmodulated carrier wave, and can operate stably even with modulated signals. Through this series of operations, the automatic frequency controller according to the present invention has two functions.

It will operate stably even for frequency modulated signals with a low carrier-to-noise ratio.

Note that the output signal of the voltage controlled oscillator 22 and the bandpass filter 1
A signal obtained by shifting the phase of the output signal of 1 by 90° by the 90° phase shifter 1.1 is supplied to the second phase detector 15, and is used to determine whether or not the automatic phase locking loop is established. Detected. Then, the switch 17 is controlled according to the output signal of the second phase detector 15, and the output signal of the rectangular wave oscillator 16 is supplied to the integrator 18 when nine phase synchronization is not established. As a result, a symmetrical triangular wave is obtained at the output of the integrator 18, which is swept through the local oscillator 4 via the voltage adder 19. In this way, performing the initial compensation operation when the pilot signal is not within the band of the bandpass filter 11 is the same as in the conventional automatic frequency controller.

〔Effect of the invention〕

As described above, the automatic frequency controller according to the present invention can exhibit an automatic frequency control function that operates stably even for a pilot signal modulated with a low carrier-to-noise ratio.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an automatic frequency controller according to the present invention, and FIG.
The figure is a system diagram of a conventional automatic frequency controller. 1...Signal input terminal, 2...Signal output terminal, 3...
- Frequency converter, 4... Local oscillator, 11... Bandpass filter. 12... Reference frequency generator, 13... First phase detector, 14... 90° phase shifter, 15... Second phase detector, 16... Square wave oscillator, 17... Switcher, 18... Integrator, 19... Voltage adder, 20...
...first loop filter, 22...voltage controlled oscillator, 23...downloader, 24...frequency phase comparator, 2
5...Second loop filter. J Figure 2

Claims (1)

[Claims] 1. In a circuit that mixes an input signal with a local oscillation signal in a frequency converter to convert the frequency, the pilot signal in the output signal of the frequency converter is passed through a bandpass filter together with the output signal of the voltage controlled oscillator. a phase detector, and negative feedback of the phase error signal from the first phase detector to the voltage controlled oscillator via a first loop filter, thereby matching the frequency of the voltage controlled oscillator with the pilot signal. the frequency of the output signal of the voltage controlled oscillator is lowered by a stepper, the frequency of the output signal of the voltage controlled oscillator is lowered, and the output signal of the reference frequency generator is supplied to a frequency phase comparator, and the error signal of the frequency phase comparator is passed through a second loop filter. , a circuit that provides negative feedback to the frequency control terminal of the local oscillator via a voltage adder, a signal that passes the band-limited signal by the bandpass filter through a 90° phase shifter, and an output signal of the voltage-controlled oscillator. and a circuit for controlling the supply of the square wave oscillator output signal to the integrator by supplying the signal to the second phase detector and controlling the switch according to the phase error signal of the second phase detector. an automatic frequency controller, wherein the symmetric triangular wave output from the integrator is supplied to a frequency control terminal of the local oscillator via the voltage adder during initial compensation.