JPH04165717A - Phase locked loop circuit - Google Patents

Abstract

PURPOSE:To reduce the time for phase synchronization establishment and to establish the synchronization of the phase locked loop by providing a loop changeover circuit selecting a loop circuit system having a low pass filter only with a control signal at phase asynchronization. CONSTITUTION:When a phase of a frequency division signal S2 of a frequency divider 2 and a phase of an output signal S3 of a reference signal generator 3 are not synchronized, an output signal S4 of a phase comparator passes through a low pass filter 5 only and when the phase synchronization establishment is detected by a switching control circuit 8 is detected, the signal passes through the low pass filter 5 and a loop filter 6 to control a voltage controlled oscillator 1. Thus, the low pass filter 5, the loop changeover device 9 and the switching control circuit 8 are provided to select the combination of the low pass filter 5 and the loop filter 6 with the loop changeover device 9 thereby preventing phase synchronization unestablishment due to leakage of a reference signal without delaying the establishment time of phase synchronization even when the phase comparison frequency is low.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a phase-locked loop circuit, and particularly to a phase-locked loop circuit that aims to shorten the time to establish phase locking even when the phase comparison frequency is low speed, and to prevent leakage of reference frequencies, etc. The present invention relates to a phase-locked loop circuit that can prevent failure of phase synchronization due to interference.

[Conventional technology]

In the conventional phase-locked loop circuit, as shown in FIG. 2, the output signal s1 of the voltage controlled oscillator 1 is divided into 1/N
The frequency is divided and becomes a frequency-divided signal s2, which is input to the phase comparator 4.
The output signal S3 of the reference signal oscillator 3 and the frequency-divided signal S2 are compared by the phase comparator 4. Now, reference signal oscillator 3
output signal V, amplitude VIN angular frequency ω2, initial phase θ
.

In (1), a and vi are expressed by equation (1).

Vi =V+ s in (ω1 to 1θ+ (t)
) H) Amplitude VC+ and angular frequency ω of a frequency-divided signal v0 obtained by dividing the output signal S1 of vcot by N. Initial phase θ. (1)
Then, VO is expressed by equation (2).

VO=Vo COs (ω. 10.(t) )−(2
) The output signal Ve of the phase comparator 4 is expressed by equation (3), where Kd is the conversion gain of the phase comparator.

Ve = Kd (s i n (((IJ, +ω.)
+θ1(t) 10. (1))) +5in((ω1-ω.)+01(t)-〇.(1))
)...(3) Since the high frequency band of this output is removed by the loop filter 6, the output signal Vd of the loop filter 6 is now ω,=ω. If (
4) It is expressed by the formula.

Vd=KdF(S)s in CO,(t)−θo(
t))...(4) This signal is further amplified by the amplifier 7 to produce an output signal v
When d' is an amplification factor A, it is expressed by equation (5).

Vd' = AKdF(S) sin [:θ+D)-
〇, (1))...(5) That is, the output signal vd' becomes a control signal for the voltage controlled oscillator 1. The 86 signal (vd) in equation (4) is S3 (vt
) and 82 (v, ), that is, θ, (t)
−〇. A phase-locked loop was formed by controlling the oscillation frequency f of the voltage-controlled oscillator so that (t)=O.

Problems to be Solved by the Invention C] The conventional phase-locked loop circuit described above synchronizes the phase by comparing the divided signal S2 of the oscillation frequency of the voltage controlled oscillator 1 with the output signal S3 of the reference signal oscillator. As the frequency (divided signal) for phase comparison becomes lower, the bandwidth of the loop filter must be narrowed. Therefore, there is a drawback that it takes time to establish phase synchronization due to the delay when passing through the loop filter. Also, if there is a leakage of the reference signal in the output of the phase comparator, Vi shown in equation (1) is output, so ve1' in equation (5) becomes vd' in equation (6). become.

Va ”=AKdF(S)s in CO1(t)
−〇, (1) +V+ s in (ωt to 1θI(t
)) ) - (G Therefore, even if the phase-locked loop works so that vt (U = θ. (1)), vd is almost A K
The control voltage does not become d F (S), and there is a drawback that synchronization of the phase-locked loop cannot be established.

[Means to solve the problem]

The phase-locked loop circuit of the present invention includes a voltage-controlled oscillator, a phase comparator that performs a phase comparison between a frequency-divided signal obtained by dividing the output signal of the voltage-controlled oscillator, and a reference signal, and a phase-locked loop circuit that divides the output signal of the phase comparator into a predetermined value. In a phase-locked loop circuit that passes through a band loop filter and then amplifies it and returns it as a control voltage of the voltage controlled oscillator, a low-pass filter that removes leakage of the reference signal present in the output signal of the phase comparator. a filter, a switching control circuit that monitors the output signal of the phase comparator, determines phase synchronization or phase asynchrony, and outputs a control signal; A loop circuit system is provided in which the loop filter is connected in series, and a loop switching circuit is provided that switches to a loop circuit system having only the low-pass filter in response to a control signal when the phase is not synchronized.

〔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 FIG. 1, circuits with the same symbols as those in the conventional example of FIG. 2 have the same configuration and function. That is, in this embodiment, a low frequency filter 5, a switching control circuit 8, and a loop switching circuit 9 for changing the form of the loop are added.

Next, the operation of this embodiment will be explained. Frequency division signal S of frequency divider 2
2 and the output signal S3 of the reference signal generator 3 are not synchronized in phase, the loop switch 9 is on the terminal 2-3 side, and the output signal S4 of the phase comparator is passed through the low-pass filter. 5 and is amplified by amplifier 7 to control voltage controlled oscillator 1. At this time, by making the bandwidth of the low-pass filter 5 5 to 10 times wider than that of the loop filter 6, the phase synchronization establishment time can be shortened.

When the switching control circuit 8 detects the establishment of phase synchronization, the loop switch 9 is switched to the terminal 1-3 side, and the output signal S4 passes through the low-pass filter 5 and the loop filter 6, and is amplified by the amplifier 7. Controls the voltage controlled oscillator 1. In this case, even if the output signal S4 contains leakage of the reference frequency, the reference frequency component can be sufficiently removed by the low-pass filter 5, so the output signal S7 will have only a DC component, and the phase-locked loop system will be stabilized. can be operated to establish synchronization.

〔Effect of the invention〕

As explained above, the present invention includes a low-pass filter, a loop switch, and a switching control circuit, and by switching the combination of the low-pass filter and the loop filter using the loop switch, the phase comparison frequency can be adjusted. without delaying the establishment time of phase synchronization even at low
In addition, it is possible to prevent failure of phase synchronization due to reference signal leakage.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional phase-locked loop circuit. DESCRIPTION OF SYMBOLS 1... Voltage controlled oscillator, 2... Frequency divider, 3... Reference signal oscillator, 4... Phase comparator, 5... Low pass filter, 6... Loop filter, 7... Amplifier, 8
...Switching control circuit, 9...Loop switching device.

Claims (1)

[Claims] 1. A voltage controlled oscillator, a phase comparator that performs a phase comparison between a frequency-divided signal obtained by dividing the output signal of the voltage controlled oscillator and a reference signal, and a phase comparator that compares the phase of the divided signal obtained by dividing the output signal of the voltage controlled oscillator with a reference signal, and In a phase locked loop circuit that passes through a band loop filter and then amplifies and returns as a control voltage of the voltage controlled oscillator, a low pass that removes leakage of the reference signal present in the output signal of the phase comparator. a filter, a switching control circuit that monitors the output signal of the phase comparator, determines phase synchronization or phase asynchrony, and outputs a control signal; A loop circuit system in which the loop filter is connected in series, and a loop switching circuit that switches to a loop circuit system having only the low-pass filter in response to a control signal when the phase is not synchronized. Synchronous loop circuit. 2. The phase-locked loop circuit according to claim 1, wherein the passband of the low-pass filter has a passband that is 5 to 10 times larger than the passband of the loop filter.