JPH0346413A - Phase locked loop circuit - Google Patents

Abstract

PURPOSE:To attain the phase pull-in with a wide frequency range by detecting a level of a frequency error signal, discriminating the level with a threshold level, switching the level of a frequency error signal fed to a voltage controlled oscillator so as to eliminate the effect of an interrupt signal or distortion. CONSTITUTION:A threshold voltage of a control voltage detection circuit 61 of a control voltage changeover means 6 is set between an output voltage of a frequency error detection means 5 with the production of pseudo locking caused therein and an output voltage of the means 5 with interference or distortion caused therein in advance. When an output voltage of the means 5 is higher than the threshold voltage, it is decided as the occurrence of pseudo pull-in phenomenon, and the output of a voltage changeover device 62 is switched to input the output voltage of the means 5 as it is to a 2nd input terminal 8 of a voltage controlled oscillator 3 thereby controlling the frequency of the oscillator 3. On the other hand, when the output voltage of the means 5 is lower than the threshold level, it is decided to be in the phase pull-in state even with interruption or distortion. Then the output of the changeover device 62 is switched to input a preset control voltage to the terminal 8 so that the reference phase carrier (b) has the frequency f0 of the input signal (a) thereby keeping the frequency of the carrier (b) to the frequency f0.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to a phase synchronization circuit that regenerates a synchronization signal from a phase-modulated digital signal, and is particularly applicable to a phase synchronization circuit that reproduces a synchronization signal from a phase-modulated digital signal. This invention relates to a phase-locked circuit capable of synchronous pull-in.

〔overview〕

The present invention provides a phase locked circuit configured to compare an input signal with a reference phase carrier output from a voltage controlled oscillator, generate a phase error signal and a frequency error signal, and control the voltage controlled oscillator using these error signals. , detecting the magnitude of the frequency error signal, determining the magnitude using a predetermined threshold, and switching the magnitude of the frequency error signal supplied to the voltage controlled oscillator according to the determination result. This eliminates the effects of interference signals and distortion, and allows for a wide frequency pull-in range.

[Conventional technology]

Conventionally, this type of phase synchronization circuit includes a four-phase phase detector 2 that detects the phase of an input signal a input from a signal input terminal l using a reference phase carrier wave, as shown in FIG. A voltage controlled oscillator 3 which has two input terminals, a terminal 7 and a second input terminal 8, controls the oscillation frequency by these input terminals, and outputs a reference phase carrier wave, and is coupled to the output of the phase detector 2, Phase error detection means 4 detects the phase error between the input signal and the reference phase carrier wave and outputs the average voltage as a phase error signal C; frequency error detection means 5 for detecting a frequency error of , and outputting the average voltage as a frequency error signal d;
The frequency of the reference phase carrier wave was controlled by directly inputting the output voltage of the phase error detection means 4 to the first input terminal 7 and the output voltage of the frequency error detection means to the second input terminal 8.

Here, the phase error detection means 4 includes an exclusive OR circuit 41 and a reduction filter 42, and the frequency error detection means 5 includes a delay circuit 51, an exclusive OR circuit 52, a synthesis circuit 53, and a low frequency A filter 54 is included.

[Problem that the invention seeks to solve]

The conventional phase-locked circuit described above directly supplies the average voltage of the frequency error signal to the second input terminal 8 of the voltage controlled oscillator 3, so if the input signal is affected by an interference signal and the spectrum of the input signal is deformed. For example, as shown in FIGS. 3(a) and (b), the spectrum of the input signal is
When the transformation is performed as shown in (a) to (a) of the same figure, the average voltage of the frequency error signal changes as if the frequency of the input signal were shifted, and the frequency of the reference phase carrier wave changes to f.

from f'.

This has the drawback that the phase entrainment frequency range becomes narrower.

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-locked circuit having a wide synchronous pull-in frequency range without causing a pseudo pull-in phenomenon by eliminating the above-mentioned drawbacks.

[Means for solving problems]

The present invention has a phase detector that detects the phase of an input signal using a reference phase carrier wave, and a first and second input terminal, and changes the oscillation frequency by a voltage supplied to these input terminals to output the reference phase carrier wave. a voltage controlled oscillator that detects a phase error between the input signal and the reference phase carrier wave using the output of the phase detector, generates a phase error signal, and supplies the generated phase error signal to a first input terminal of the voltage controlled oscillator. and frequency error detection means that detects a frequency error between the input signal and the reference phase carrier wave using the output of the phase detector, generates a frequency error signal, and supplies the generated frequency error signal to a second input terminal of the voltage controlled oscillator. In a phase locked circuit,
Detecting the magnitude of the frequency error signal voltage, determining the magnitude of the detected voltage by comparing it with a predetermined threshold voltage, and supplying the voltage to the second input terminal of the voltage controlled oscillator according to the determination result. The present invention is characterized by comprising a control voltage switching means for switching the magnitude of the voltage.

[Effect]

The frequency error signal between the input signal and the reference phase carrier wave becomes very large when the pseudo-entrainment phenomenon occurs because the frequency deviation is large.

On the other hand, since the frequency shift of the reference phase carrier wave due to interference signals and distortion is small, the magnitude is small at the time of this synchronization pull-in. Therefore, a pseudo pull-in of the magnitude of the frequency error signal is used as a threshold value in the control voltage switching means. Set between the value at the time of the phenomenon and the value at the time of synchronization pull-in. When the frequency error signal is above the threshold value, the frequency error signal is supplied as it is to the second input terminal of the voltage controlled oscillator, and when it is below the threshold value, a signal of a normal prescribed magnitude is supplied.

Therefore, it is possible to perform synchronous pull-in in a wide frequency range without causing a pseudo pull-in phenomenon and without frequency deviation of the reference phase carrier wave.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

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

This embodiment has a phase detector 2 which detects the phase of an input signal a input to a signal input terminal 1 using a reference phase carrier wave, and a first and second input terminal 7 and 8. a voltage controlled oscillator 3 that changes its oscillation frequency depending on the voltage supplied to the oscillator 8 and outputs a reference phase carrier wave;
A phase error detection means 4 detects the phase error between the input signal a and the reference phase carrier wave by the output of the phase detector 2, generates a phase error signal C, and supplies it to the first input terminal 7 of the voltage controlled oscillator 3; The frequency error detection means 5 detects the frequency error between the input signal a and the reference phase carrier wave by the output of the wave detector 2, generates a frequency error signal d, and supplies the generated frequency error signal d to the second input terminal 8 of the voltage controlled oscillator 3. In a phase-locked circuit, the present invention is characterized by detecting the magnitude of the frequency error signal voltage, determining the magnitude of the detected voltage using a predetermined threshold voltage, and adjusting the voltage according to the determination result. A control voltage switching means 6 is provided for switching the magnitude of the voltage supplied to the second input terminal 8 of the controlled oscillator 3.

Furthermore, the phase error detection means 4 includes an exclusive OR circuit 41 that takes the exclusive OR of two outputs from the phase detector 2, and a phase error that removes high frequency components in the output of this exclusive OR circuit 41. The frequency error detection means 5 includes a delay circuit 51 that provides a predetermined delay to one output of the phase detection circuit 2;
1 and the other output of the phase detection circuit 2; and a synthesis circuit that subtracts the output of the exclusive OR circuit 41 from the output of the exclusive OR circuit 52. 53, and a low-pass filter 54 that removes high frequency components from the output of the synthesis circuit 53 and outputs a frequency error signal d.The control voltage switching means 6 inputs the frequency error signal d and determines the magnitude of the voltage. A control voltage detection circuit 61 that compares the frequency error signal with a predetermined threshold voltage and outputs a switching signal e, and outputs the frequency error signal d as is or outputs a signal having a normal specified voltage according to the input switching signal e. A control voltage switch 62 that switches whether to output
Contains.

Next, the operation of this embodiment will be explained.

Input signal a applied to signal input terminal 1 is input to phase detector 2, where phase detection is performed using the output signal of voltage controlled oscillator 3 as a reference phase carrier. The two outputs of the phase detector 2 are input to the phase error detection means 4, subjected to a logical operation in an exclusive OR circuit 41, a phase error signal C is formed, and a high frequency component is extracted in a low pass filter 42. After being removed, it is supplied to the first input terminal 7 of the voltage controlled oscillator 3 to control the oscillation frequency, and a part of it is input to the synthesis circuit 53 of the frequency error detection means 5.

Further, the two outputs of the phase detector 2 are branched between the phase error detection means 4, and one signal is input to the delay circuit 51 of the frequency error detection means 5, and after passing through the delay circuit 51, the exclusive logic It is input to one input of the summation circuit 52.

The other output of the phase detector 2 is input to the other input of the exclusive OR circuit 52 of the frequency error detection means 5, is subjected to a logical operation with the signal that has passed through the delay circuit 51, and is sent to the synthesis circuit 53. is input. The output of the exclusive OR circuit 52 includes a phase error signal C in addition to the frequency error signal, but the phase error signal C is canceled out in the synthesis circuit 53, and the output of the synthesis circuit 53 is the frequency error signal d. only,
After high frequency components are removed through the low-pass filter 54, the signal is input to the control voltage switching means 6.

Here, if a pseudo-entrainment phenomenon occurs, the input signal a
Since the frequency error between
Focusing on the fact that when an interference signal or distortion occurs, the output voltage of the frequency error detection means 5 becomes low because the frequency error is small, the control voltage detection circuit 61 of the control voltage switching means 6
The threshold voltage of is set in advance to be between the output voltage of the frequency error detection means 5 when a pseudo-entrainment phenomenon occurs and the output voltage of the frequency error detection means 5 when interference or distortion occurs, If the output voltage of the frequency error detection means 5 is higher than the threshold voltage, it is determined that a pseudo pull-in phenomenon has occurred, and the control voltage is switched so that the output voltage of the frequency detection means 5 is directly inputted to the second input terminal 8. The output of the voltage controlled oscillator 3 is switched to control the oscillation frequency of the voltage controlled oscillator 3.

On the other hand, if it is lower than the threshold voltage, it is determined that the synchronous pull-in state is present even if an interference signal or distortion occurs, and the reference phase carrier wave is set to the normal frequency f of the input signal a. Switch the output of the control voltage switch 62 so that the control voltage set in advance as follows is input to the second input terminal 8,
The frequency of the reference phase carrier wave is f. to hold.

In this embodiment, a two-phase phase locked circuit was explained, but
The same applies to the phase-locked circuit of the present invention in the case of an N-phase phase-locked circuit (N is an integer of 2 or more).

〔Effect of the invention〕

As explained above, according to the present invention, the average voltage of the frequency error signal is detected, and the frequency error between the input signal and the reference phase carrier wave is determined whether the frequency error is caused by a pseudo-entrainment phenomenon or is caused by an interference signal or distortion. If it is a pseudo-entrainment phenomenon, change the frequency of the reference phase carrier wave to avoid the pseudo-entrainment phenomenon, and if it is due to an interference signal or distortion, maintain the frequency of the reference phase carrier wave. It is possible to obtain a phase-locked circuit having a wide synchronous pull-in frequency range without causing a pseudo pull-in phenomenon, and the effect is great.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing a conventional example. FIGS. 3(a) and 3(a) are explanatory diagrams showing the spectrum of an input signal in the present invention. 1... Signal input terminal, 2... Phase detector, 3...
Voltage controlled oscillator, 4... Phase error detection means, 5...
Frequency error detection means, 6... Control voltage switching means, 7.
...-th input layer child, 8... second input terminal, 41.52
... exclusive OR circuit, 42.54 ... low-pass filter, 51 ... delay circuit, 53 ... synthesis circuit, 61 ...
- Control voltage detection circuit, 62... Control voltage switch, a.
...Input signal, b...Reference phase carrier wave, C...Phase error signal, d...Frequency error signal, e...Switching signal.夷bag例昂 1 Ensemble 11 昂 2 圓 Input Signal Skutram 昂 3 times

Claims (1)

[Claims] 1. A phase detector that detects the phase of an input signal using a reference phase carrier wave; and a phase detector having first and second input terminals, and changing the oscillation frequency by the voltage supplied to these input terminals, a voltage controlled oscillator that outputs a phase carrier wave; and a phase error between the input signal and the reference phase carrier wave is detected by the output of the phase detector, a phase error signal is generated, and the phase error signal is supplied to a first input terminal of the voltage controlled oscillator. phase error detection means; and frequency error detection means that detects a frequency error between the input signal and the reference phase carrier wave using the output of the phase detector, generates a frequency error signal, and supplies the generated frequency error signal to a second input terminal of the voltage controlled oscillator. Detecting the magnitude of the frequency error signal voltage, determining the magnitude of the detected voltage by comparing it with a predetermined threshold voltage, and controlling the voltage according to the determination result. 1. A phase synchronized circuit comprising control voltage switching means for switching the magnitude of the voltage supplied to a second input terminal of an oscillator.