JPH03101516A - Automatic frequency control circuit - Google Patents

Abstract

PURPOSE:To vary a loop band continuously without unlocking the phase locked loop by feeding back a phase error to a voltage controlled type local frequency oscillator through a digital filter comprising an A/D converter, a logic controller and a D/A converter. CONSTITUTION:The frequency of an input signal is converted by an output signal of a voltage controller local frequency oscillator 6 at a frequency converter 1. The phase of the frequency-converted signal is compared with the phase of an oscillating signal from a reference local oscillator 7 at a phase comparator. Then the phase error is fed back to the oscillator 6 through an A/D converter 3, a logic controller 4 and a D/A converter 5 to control the frequency. Thus, the output signal of the oscillator 6 is locked with the phase of the input signal. Thus, the loop band of automatic frequency control is continuously changed from a wide band into a narrow band. Thus, a shock given onto the loop of automatic frequency control is small and the phase locking is not unlocked.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic frequency control circuit, and more particularly to an automatic frequency control circuit using a digital filter calculated by a logic controller as a loop filter for automatic frequency control.

[Conventional technology]

Conventionally, this type of automatic frequency control circuit includes a frequency converter, a phase comparator that performs a phase comparison with a reference local signal, a loop filter, and a loop filter that is driven by the output of the loop filter to detect the local signal of the frequency converter. It consists of a voltage-controlled local frequency oscillator that generates Further, the loop filter uses a filter configured with a resistor and a capacitor.

[Problem to be solved by the invention]

The conventional automatic frequency control circuit described above uses a loop filter composed of a resistor and a capacitor, so
When changing the loop band, it is necessary to change the loop filter, for example, and there is a possibility that the phase synchronization will be lost. Then, there is a problem that phase synchronization that is off by -degree requires a waiting time until phase synchronization is re-phased.

An object of the present invention is to provide an automatic frequency control circuit that does not cause out-of-phase synchronization even when changing the loop band.

[Means to solve the problem]

The automatic frequency control circuit of the present invention includes a frequency converter, a phase comparator that compares the phase of a frequency-converted signal based on an output signal of a reference local oscillator, and an A/D converter that converts a phase error into a digital value. a logic controller that calculates the converted digital value; a D/A converter that converts the calculated value into an analog value; and a signal that is fed back from this analog value and is output to the frequency converter. It is equipped with a voltage controlled local frequency oscillator.

[Effect]

In this configuration, the phase error is determined by an A/D converter, a logic controller,
By feeding back to the voltage controlled local frequency oscillator using a digital filter constituted by a D/A converter, it becomes possible to change the loop band continuously without losing phase synchronization.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

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

In the figure, a frequency converter l converts an input signal into a reference frequency using a voltage-controlled local oscillator 6, a phase comparator 2 compares the phases of the output signal of the frequency converter 1 and the output signal of the reference local oscillator 7, , an A/D converter 3 that converts the DC output voltage of the phase comparator 2 into a digital value, a logic controller 4 that calculates a digital filter based on the digital value output from the A/D converter 3, and a logic control A D/A converter 5 that converts the calculation output of the device 4 into an analog voltage;
a voltage-controlled local frequency oscillator 6 whose oscillation frequency changes linearly based on the analog voltage output from the A converter 5;
It is equipped with a highly stable reference local oscillator 7.

Here, the A/D converter 3. Logic controller 4° and D/
The A converter 5 constitutes a digital filter.

According to this configuration, the frequency of the input signal is converted by the output signal of the voltage-controlled local frequency oscillator 6 in the frequency converter 1. The phase of this frequency-converted signal is compared with the oscillation signal from the reference local oscillator 7 by a phase comparator,
The phase error is determined by A/D converter 3. Logic controller 4. The signal is fed back to the voltage-controlled local frequency oscillator 6 through the D/A converter 5, and its frequency is controlled. Thereby, the output signal of the voltage controlled local frequency oscillator 6 is synchronized with the phase of the input signal.

At that time, the loop band of automatic frequency control is controlled by logic controller 4.
The constant of the digital filter can be continuously set arbitrarily. Therefore, the loop band of automatic frequency control can be changed continuously from a wide band to a narrow band, and since it is changed continuously, the impact on the automatic frequency control loop is small and phase synchronization does not occur.

〔Effect of the invention〕

As explained above, the present invention uses a digital filter calculated by a logic controller as a loop filter for automatic frequency control, so that the loop band for automatic frequency control can be continuously changed from wide band to narrow band without losing phase synchronization. This can be done in a number of ways, and is particularly effective when the S/N ratio of the input signal is poor.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. 1... Frequency converter, 2... Phase comparator, 3...
A/D converter, 4... logic controller, 5... D/A converter, 6... voltage controlled local frequency oscillator.

Claims (1)

[Claims] 1. A frequency converter, a phase comparator that compares the phase of the frequency-converted signal based on the output signal of the reference local oscillator, and an A/D converter that converts the phase error into a digital value;
A logic controller that calculates the converted digital value, a D/A converter that converts the calculated value into an analog value, and a voltage control that controls the signal to which this analog value is fed back and output to the frequency converter. An automatic frequency control circuit comprising a type local frequency oscillator.