JPH0738584B2 - Phase locked loop circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase locked loop circuit (hereinafter referred to as a PLL circuit) which outputs an output signal accurately even when an abnormality occurs in an input signal.

[0002]

2. Description of the Related Art Conventionally, phase locked loop (PLL) technology has been widely used. The phase lock loop originally removes a high frequency jitter component of the input frequency.
Therefore, the output signal has a characteristic that it does not change abruptly even if the input signal is somewhat abnormal.

In recent years, a PLL technique has been used for so-called self-clock extraction, in which a clock is extracted from a signal when a signal is extracted from a recording medium and an information signal is read by this clock. In such a case, a large burst error will be added to the information unless very accurate clock extraction is performed.

As described above, in recent years, a high performance PLL circuit has been required. FIG. 5 shows an example of a basic PLL circuit. In FIG. 5, reference numeral 1 is a phase comparator for comparing the phases of the input signal fi and the output signal fo, the output of which is connected to the amplifier 2 and the output of the amplifier 2 is a voltage-frequency converter, which is a voltage control type. The oscillator 3 is controlled. The output of this voltage controlled oscillator is the output of the PLL circuit, and this output is also fed back to the phase comparator 1.

FIG. 6 is a frequency characteristic diagram of the amplifier 2. The amplifier 2 is generally a low pass filter as shown in FIG. When the open loop gain of the system is G, fn is the gain intersection frequency. fn determines the response speed of the system. It is chosen well below the input frequency to eliminate jitter in the input signal. However, if it is too low, the response speed of the system will be low. For example, in a high-density recording medium, the frequency of the input signal is about 1 MHz, while fn is required due to the need for high-speed address search.
Is selected above 1 KHz. That is, fn is subject to the above-mentioned restrictions and cannot be freely determined. fn = 1
Consider the case where an abnormality occurs in the input signal fi at KHz (FIG. 5). Note that the fluctuation frequency of the input signal fi is often about 5 to 30 Hz. For example, this fluctuating frequency is set to 10 Hz.

FIG. 7 shows the output of the phase comparator 1 when the input signal fi has no abnormality such as noise. Input signal fi
The fundamental frequency of the output of this phase comparator is 10 Hz because the fluctuating frequency of 10 Hz is 10 Hz.

[0007]

However, when an abnormality occurs in the input signal, the output of the phase comparator is disturbed.
When the input signal has a very high frequency, the output of the phase comparator may become zero. In this case, the gain crossover frequency of the system is 1 KHz, which is sufficiently higher than the fluctuation frequency of 10 Hz, so that the output frequency of the voltage controlled oscillator 3 largely deviates during this period. If fn can be adjusted to the fluctuating frequency of 10 Hz, interpolation that compensates for such a shift is possible. However, fn cannot be set to such a low value from the system response as described above.

According to the present invention, as described above, even when an abnormality occurs in the input signal, the abnormality does not appear in the output signal.
It is an object to provide an LL circuit.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a phase comparator for comparing the phases of an input signal and an output signal, and a resonance circuit connected to the output side of the phase comparator.
It is characterized by including a low-pass filter whose wave number substantially matches the fluctuation component frequency of the input signal of the phase comparator, and an oscillator whose output signal oscillation frequency is controlled according to the output of the low-pass filter. . A voltage-controlled oscillator is generally used as the oscillator.

[0010]

According to the present invention, the oscillation frequency can be made to follow the fluctuation frequency component of the input signal extremely accurately in accordance with the fluctuation of the input component even when the output from the phase comparator cannot be obtained. it can.

[0011]

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

FIG. 1 shows a block diagram of an embodiment of the present invention, and the same parts as those described in FIG. 5 are designated by the same reference numerals. In this (FIG. 1), the phase comparator 1 is connected to the input side of the loop switch 51, and the output end of the phase comparator 1 is connected to the phase abnormality detector 52. The output terminal of the loop switch 51 is connected to the resonance circuit 53, and the output thereof controls the voltage controlled oscillator 3.

The resonance circuit 53 is a secondary low-pass filter as shown in FIG. This resonance frequency f ⁰ is made to substantially match the fluctuation component frequency of the input signal. The response frequency of the system when the loop is closed is determined by the gain intersection frequency fn. Now, when an abnormality occurs in the high frequency input signal and the output of the phase comparator 1 becomes zero due to this, the loop is equivalently cut during this period. In this case, the phase abnormality detector 52 becomes unnecessary. Since the resonance of the system at the time of open loop is f ⁰ of the resonance circuit 53, the output of the resonance circuit 53 changes just in agreement with the fluctuation component frequency of the input signal. Therefore, the output of the resonance circuit 53 changes in the same manner as in FIG. 7, and the output of the voltage controlled oscillator 3 changes in the same manner as in the case where there is almost no damage.

FIG. 3 is a block diagram showing another embodiment of the present invention. In this (FIG. 3), the same components as those described in (FIG. 1) are designated by the same reference numerals.
In FIG. 3, the resonance circuit 5 having the characteristics shown in FIG.
Instead of 3, first-order low-pass filter 6 connected in cascade
A resonance circuit 53 'composed of 1 and a bandpass filter 62 is used. A curve 81 in FIG. 4 shows the characteristic of the first-order low-pass filter 61, and a curve 82 shows the characteristic of the second-order resonant circuit. If the resonance frequency of the second-order bandpass filter is adjusted to the frequency of the fluctuation component of the input signal, the same operation as in the case of (FIG. 2) is performed.

[0015]

As described above, according to the present invention, with a very simple structure, even when an abnormality occurs in the input signal and the output from the phase comparator cannot be obtained, the fluctuation of the input component is extremely small. The oscillation frequency can be accurately followed by the fluctuation frequency component of the input signal.

[Brief description of drawings]

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

FIG. 2 is a gain vs. frequency characteristic diagram of the resonance circuit according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a second embodiment of the present invention.

FIG. 4 is a gain vs. frequency characteristic diagram of the resonance circuit according to the second embodiment of the present invention.

FIG. 5 is a block diagram showing an example of a conventional PLL circuit.

FIG. 6 is a diagram showing the amplification factor vs. frequency characteristic of a conventional PLL circuit.

FIG. 7 is an operation explanatory diagram of the PLL circuit of FIG. 5;

[Explanation of symbols]

 1 Phase Comparator 3 Voltage Controlled Oscillator 53, 53 'Resonant Circuit 61 Low Pass Filter 62 Band Pass Filter

Claims (1)

[Claims] 1. A phase comparator for comparing the phases of an input signal and an output signal, and a resonance connected to the output side of the phase comparator.
A phase-locked loop comprising: a low-pass filter whose frequency is substantially equal to a variation component frequency of the input signal of the phase comparator; and an oscillator whose output signal oscillation frequency is controlled according to the output of the low-pass filter. circuit.