JPH04111615A - Phase locked loop circuit - Google Patents

Abstract

PURPOSE:To attain quick recovery of synchronization by applying an output signal of a sweep oscillator to a differentiating circuit. CONSTITUTION:When the phase locked loop is in the lock state, since an impedance at a point 6 is zero, a sweep oscillator 5 is not oscillated and when out of synchronism takes place, since the impedance at a point 6 is changed, the sweep oscillator 5 starts oscillation and the oscillated output is fed to a differentiating circuit 7, from which a differentiated waveform output is obtained. The output waveform is fed to a voltage controlled oscillator 2 to sweep the oscillating frequency of the oscillator 2 over a wide frequency range and the synchronization recovery is applied to an input signal whose frequency is within the sweep frequency. The frequency change in the oscillating frequency of the oscillator 2 is slow in the vicinity of a reference frequency and the convergence to the reference frequency is facilitated and quick synchronization recovery is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a phase-locked circuit, and more particularly to a phase-locked circuit that reduces synchronization recovery time.

[Conventional technology]

An example of a conventional phase locked circuit is shown in FIG. In the figure, 1 is a signal input terminal, 2 is a voltage-controlled oscillator, 3 is a phase comparator that detects the phase error between the input signal and the oscillation output of voltage-controlled oscillator 2, and 4 is a low-pass filter. be. This phase comparator 3, voltage controlled oscillator 2, low pass filter 4
A sweep oscillator 5 is connected to a point 6 in a phase-locked loop consisting of.

In this phase-locked circuit, when the phase-locked loop is in a locked state, the impedance at point 6 becomes approximately 0, so the sweep oscillator 5 stops oscillating and operates as a normal phase-locked loop.

Next, when synchronization occurs, the impedance at point 6 causes the sweep oscillator 5 to start oscillating. This sweep oscillator 5
The oscillation output is applied to the voltage controlled oscillator 2, and sweeps the oscillation frequency of the voltage controlled oscillator 2 over a wide frequency range.

By sweeping the oscillation frequency of the voltage controlled oscillator 2 in this manner, synchronization can be quickly recovered for input signals within the swept frequency range. When synchronization is restored, sweep oscillator 50 oscillates and operates as a normal phase-locked loop.

Note that matters related to the phase-locked loop having such a configuration and the operation contents of the sweep oscillator 5 are explained in detail in, for example, Japanese Patent Publication No. 49-42268.
The explanation thereof will be omitted here.

[Problem to be solved by the invention]

In the conventional phase-locked circuit described above, the sweep oscillator 5 oscillates when the synchronization is out of order and sweeps the oscillation frequency of the voltage controlled oscillator, but the output waveform of the sweep oscillator 5 is a sine wave as shown in FIG. Alternatively, the waveform is obtained by clipping the peak of the sine waveform.

For this reason, the oscillation frequency of the voltage controlled oscillator 2 controlled by this waveform has a characteristic that changes rapidly near the reference frequency, making it difficult to converge the oscillation frequency to the reference frequency, and the frequency of the input signal changes to the reference frequency. There is a problem in that synchronization recovery is delayed even though the frequencies are close to each other.

An object of the present invention is to provide a phase-locked circuit that quickly recovers synchronization.

[Means for Solving the Problems] The phase locked circuit of the present invention includes a voltage controlled oscillator, a phase comparator that performs a phase comparison between an input signal and an output signal of the voltage controlled oscillator, and an output of the phase comparator. A wave generator that outputs a control voltage for a voltage controlled oscillator by filtering the voltage, a sweep oscillator that outputs a signal that sweeps the voltage controlled oscillator, and a differentiation circuit connected to the output side of the sweep oscillator. There is.

The differentiating circuit can be configured with a CR circuit, for example.

[Effect]

According to the present invention, the differentiating circuit makes the slope of the waveform of the sweep signal gentle in the vicinity of the voltage that provides the reference frequency, and the frequency change of the voltage controlled oscillator in the vicinity of the reference frequency is made gentle so that the waveform can be adjusted to the reference frequency. Facilitates convergence and enables quick synchronization recovery.

〔Example〕

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

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, l is a signal input terminal, 2 is a voltage controlled oscillator, 3 is a phase comparator that detects the phase error between the human input signal and the oscillation output of the voltage controlled oscillator 2, and 4 is a low-pass filter. , is the same as the conventional configuration shown in FIG. A differentiating circuit 7 is connected to a point 6 in the phase-locked loop composed of the phase comparator 3, the voltage controlled oscillator 2, and the low-pass filter 4. Connected.

This sweep oscillator 5 can be the same as the conventional one. Further, as the differentiating circuit 7, for example, one constructed of a capacitor C and a resistor R as shown in FIG. 2 is used.

In this phase-locked circuit, when the phase-locked loop is in a locked state, the impedance at point 6 is O, so the sweep oscillator 5 does not oscillate and operates as a normal phase-locked loop.

Next, when desynchronization occurs, the impedance at point 6 is changed, so that sweep oscillator 5 starts oscillating. The oscillation output of the sweep oscillator 5 is a sine wave or a clipped sine wave as shown in FIG. The result is a differentiated waveform like this. That is, the waveform has a gentle slope in the vicinity of the voltage that provides the reference frequency, and the slope becomes steeper as the distance from the reference frequency voltage increases.

This output waveform is then applied to the voltage controlled oscillator 2,
The oscillation frequency of the voltage controlled oscillator 2 can be swept over a wide frequency range, and synchronization recovery can be performed for input signals within the swept frequency range. At this time, the signal that sweeps the voltage controlled oscillator 2 has a gentle slope near the voltage that provides the reference frequency voltage, as described above.
The oscillation frequency of the voltage controlled oscillator 2 has a gradual change in frequency near the reference frequency, and convergence to the reference frequency is facilitated, and synchronization recovery can be quickly achieved.

When synchronization is restored, the impedance at point 6 becomes O again, and the sweep oscillator 5 stops oscillating and operates as a normal phase-locked loop.

Note that by selecting the constants of C and R constituting the differentiating circuit 7, desired sweep characteristics can be obtained. Furthermore, it goes without saying that the differentiating circuit may have other configurations.

〔Effect of the invention〕

As explained above, the present invention allows the waveform of the sweep signal to have a gentle slope in the vicinity of the voltage that provides the reference frequency by passing the output signal of the sweep oscillator through a differentiating circuit. This has the effect that frequency conversion around the frequency becomes gradual, and synchronization can be quickly recovered.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an embodiment of the phase-locked circuit of the present invention, Figure 2 is a circuit diagram of a differentiating circuit, Figure 3 is a block diagram of a conventional phase-locked circuit, and Figure 4 shows the output from the differentiating circuit. FIG. 5 is a waveform diagram of a conventional sweep signal. ■...Input terminal, 2...Voltage controlled oscillator, 3...
Phase comparator, 4...Low pass filter, 5...Sweep oscillator, 3rd

Claims (1)

[Claims] 1. A voltage controlled oscillator, a phase comparator that performs a phase comparison between an input signal and an output signal of the voltage controlled oscillator, and a filter that filters the output of the phase comparator to generate the voltage controlled oscillator. a low-pass filter that outputs a control voltage; a sweep oscillator that outputs a signal for sweeping the voltage-controlled oscillator; and a differential circuit connected to the output side of the sweep oscillator. synchronous circuit. 2. The phase locked circuit according to claim 1, wherein the differentiating circuit is constituted by a CR circuit.