JPH05110430A - Phase locked loop oscillation circuit - Google Patents

Abstract

PURPOSE:To control an operating frequency F to be F=f0 by devising a circuit such that a control is not stopped due to synchronism going out of a limit of the operating frequency F=f0+ or -DELTAf different from a conventional PLO circuit and no alarm is raised in a system on the way even when an input signal is interrupted. CONSTITUTION:A detection voltage representing an internal phase and that for an input signal phase are detected by a phase comparator 10 and its detection voltage is fed to a low pass filter 20, the result is amplified by an operational amplifier 30 and its output voltage is fed to a VCO section 50. The output signal of the operational amplifier in the phase locked loop oscillator circuit feeding back the output of the VCO section to the phase comparator is inputted to a phase change detection section 1 to detect whether or not the phase of the input signal is largely fluctuated, and the result of detection is inputted to a phase change discrimination section 2 with an input interrupt signal. When the input signal is interrupted or the phase is largely fluctuated, the output voltage is fed to the VCO section 50 by setting 0V to an analog switch 3 and the operating frequency F is automatically converged to f0, and when the phase is not largely fluctuated even in the case of the interrupted input signal received, the output voltage is fed to the VCO section 50 as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase locked oscillator (hereinafter referred to as PLO circuit), and more particularly to a voltage controlled oscillator (VC).
The present invention relates to a PLO circuit having an improved automatic frequency control function for accurately matching the frequency of O) with the average frequency of the input signal.

[0002]

2. Description of the Related Art A conventional PLO circuit, as shown in FIG.
In the phase comparator 10, the initial phase θi (201 in the figure) and VCO
The loopback phase θo (20 in the figure
5) and the phase difference | θi-θo |
02) becomes the input voltage Vi (203 in the figure) to the OP amplifier 30 after passing through the low-pass filter 20, and the output voltage Vo (204 in the figure) of the OP amplifier 30 is not largely shaken, the relay 40 operates. Instead, it is directly passed to the VCO unit 50. When the output voltage Vo is largely swung, the relay 40 operates and is passed to the VCO unit 50 as the output voltage Vo = 0V, and automatically converges to the operating frequency F = f0. Then, a part of the output of the VCO section 50
Loopback phase θo of the output of the unit 50 (205 in the figure)
Is returned to the phase comparator 10 and again compared with the initial phase θi. By repeating this, the automatic frequency control operation was performed.

[0003]

DISCLOSURE OF THE INVENTION The conventional PLO described above
The circuit is composed of an Ex-OR phase comparison circuit or the like that automatically converges to the operating frequency F = f0 when the phase of the input signal largely changes. However, when the phase comparison frequency is extremely small compared to the internal basic signal frequency, the loop gain becomes relatively small, or the loop gain when the internal and input phase synchronization points do not reach the desired points. In order to guarantee, the amplifier was put in and loop gain was raised. As a result, when the phase of the input signal largely fluctuates, the normal synchronous control operation deviates, and the control voltage of the VCO fluctuates up to the maximum offset value of the OP amplifier. As a result, the output of this PLO largely deviates from the fundamental frequency. In particular, in the case of being configured as a relay device, the frequency shift between the front and the rear has a great influence on the subsequent stage, and in the worst case, it may be mistaken for a failure in the subsequent stage. Further, although these controls are performed by a relay, there is a drawback that the relay may malfunction due to an external shock and cause a contact failure.

[0004]

A phase-locked oscillator circuit of the present invention detects a detection voltage of an internal phase and an input signal phase with a phase comparator, passes the detection voltage through a low pass filter, and then uses an OP amplifier. In the phase-locked oscillator circuit which supplies the amplified output voltage to the VCO unit and feeds back the output of the VCO unit to the phase comparator, the output signal of the OP amplifier is input to the phase change detection unit and the phase of the input signal is changed. It is detected whether or not there is a large change, and the detection result is input to the phase change determination unit together with the input disconnection signal. If the input signal is disconnected or the phase is greatly changed, the output voltage is set to 0 V by the analog switch and the VCO Supplied to the operating section and operating frequency F = f0
On the contrary, if the phase does not largely change even when the input signal is broken, the output voltage is directly supplied to the VCO section.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In this embodiment, a phase change detector 1, a phase change determiner 2, and an analog switch 3 are added to the conventional circuit.

Next, the operation of this circuit will be described. The phase comparator 10 compares the initial phase θi (101 in the figure) and the loopback phase θo (108 in the figure) which is the output of the VCO unit 50, and the phase difference | θi−θo | (102 in the figure) is calculated. After passing through the low-pass filter 20, it becomes the input voltage Vi (103 in the figure) to the OP amplifier 30. Here, when the input voltage Vi (103 in the drawing) to the OP amplifier 30 changes by Δv, the output voltage changes as Vo = 0V ± Δvo.

This output voltage Vo (104 in the figure) is input to the phase change detector 1 to detect whether or not the phase of the input signal has changed significantly. The detection result 105 is input to the phase change determination unit 2 together with the input disconnection signal 106. Input cut,
Alternatively, if the phase is largely changed, the determination result 107
Switches the analog switch 3 and the output voltage Vo = 0V
Is passed to the VCO unit 50 and automatically converges to the operating frequency F = f0. Even if the input is disconnected, if the phase is not largely changed, the determination result 107 passes the output voltage Vo = 0 V ± Δvo to the VCO unit 50 without changing the analog switch 3.

Further, a part of the output of the VCO section 50 is converted to VC.
Loopback phase θo of the output of the O unit 50 (10 in the figure
8) is returned to the phase comparator 10 and the initial phase θi is returned again.
(101 in the figure). Automatic frequency control is performed by repeating the above.

[0009]

As described above, according to the present invention, the conventional P
It is possible to control to F = f0 without raising an alarm not only in the case of swinging off at the limit point of the operating frequency F = f0 ± Δf as in the case of the LO circuit but also in a system in the middle when the input signal is cut off. Further, by using an analog switch instead of the relay, there is an effect that a mechanical defect can be removed, and if a level is set in advance in the analog switch, intentional frequency control can be performed.

[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 PLO circuit.

[Explanation of symbols]

 1 Phase Change Detection Section 2 Phase Change Judgment Section 3 Analog Switch 10 Phase Comparator 20 Low-pass Filter 30 OP Amplifier 40 Relay 50 VCO Section

Claims (1)

[Claims] 1. A detection voltage of an internal phase and an input signal phase is detected by a phase comparator, the detected voltage is passed through a low pass filter, and then an output voltage amplified by an OP amplifier is supplied to a VCO section. In a phase-locked oscillator circuit that feeds back the output of a VCO unit to the phase comparator, the output signal of the OP amplifier is input to a phase change detection unit to detect whether or not the phase of the input signal has significantly changed, and the detection is performed. The result is input to the phase change determination unit together with the input disconnection signal, and if the input signal is disconnected or the phase greatly fluctuates, the output voltage is supplied to the VCO unit as 0 V by the analog switch, and the operating frequency F
= F0, and if the phase does not fluctuate significantly even when the input signal is broken, the output voltage is directly changed to the VC
A phase-locked oscillating circuit characterized by supplying to the O section.