JPH0459809B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a phase lock loop circuit (hereinafter referred to as a PLL circuit) that accurately outputs an output signal even when an abnormality occurs in an input signal.

Conventional configuration and its problems Phase lock loop (PLL) technology has been widely used in the past. The phase lock loop originally removes high frequency jitter components of the input frequency. Therefore, the output signal has a characteristic that the output signal does not change suddenly even if there is some abnormality in the input signal.

In recent years, when extracting a signal from a recording medium, a clock is extracted from the signal, and this clock is used to read the information signal, so-called self-clock extraction.
PLL technology is used. In such a case, a large burst error will be added to the information unless very accurate clock extraction is performed.

In this way, in recent years, high performance PLL circuits have been required.

Figure 1 shows an example of a basic PLL circuit. In Figure 1, 1 is a phase comparator that compares the phases of input signal _i and output signal _p , the output of which is connected to amplifier 2, and the output of amplifier 2 is a voltage-controlled oscillator that is a voltage-frequency converter. Control 3. 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. 2 is a frequency characteristic diagram of the amplifier 2.

As shown in FIG. 2, the amplifier 2 is generally a low-pass filter. The open loop gain of the system is G
Then, _o is the gain intersection frequency. _o determines the response speed of the system. This is chosen sufficiently lower than the input frequency to remove jitter in the input signal. However, if it is too low, the response speed of the system will become low. For example, in high-density recording media, the frequency of the input signal is about 1MHz;
Due to the need for high-speed address search, etc., _o is selected to be 1KHz or higher. In other words, _o is subject to the above-mentioned restrictions and cannot be freely determined. Let us consider the case where an abnormality occurs in the input signal _i in Fig. 1 when _o = 1KHz. Note that the fluctuation frequency of the input signal _i is often about 5 to 30 Hz. For example, let this fluctuating frequency be 10Hz.

FIG. 3 shows the output of the phase comparator 1 when there is no abnormality such as noise in the input signal _i . Since the fluctuation frequency of the input signal _i is 10 Hz, the fundamental frequency of the output of this phase comparator is 10 Hz.

However, if an abnormality occurs in the input signal, the output of the phase comparator will be greatly disturbed as shown at 42 in FIG. Since the gain intersection frequency of the system is 1 KHz, which is sufficiently higher than the fluctuation frequency of 10 Hz, the output frequency of the voltage-controlled oscillator 3 deviates significantly during this period. By detecting such an abnormality, the dashed line 4 in Fig.
It is sufficient if interpolation can be performed as in 4. If _o can be made to match the fluctuating frequency of 10Hz, such interpolation is possible. However, as mentioned above, due to the response of the system, _o cannot be set to such a low value.

Purpose of the Invention The present invention prevents abnormalities from appearing in the output signal even when an abnormality occurs in the input signal as described above.
The purpose is to provide a PLL circuit.

Structure of the Invention The present invention provides a phase comparator that compares the phases of an input signal and an output signal, a resonant circuit having a resonance whose resonant frequency almost matches a fluctuation component of the input frequency, and having characteristics of a low-pass filter; The oscillator has an oscillator whose oscillation frequency is controlled according to the output of the resonant circuit. Note that a voltage controlled oscillator is generally used as the oscillator.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 5 shows a block diagram of an embodiment of the present invention, and parts similar to those described in FIG. 1 are designated by the same reference numerals. In FIG. 5, the phase comparator 1 is connected to the input side of a loop switch 51, and its output end is connected to a phase abnormality detector 52. The output end of the loop switch 51 is connected to a resonant circuit 53, and its output controls the voltage controlled oscillator 3.

The resonant circuit 53 is a secondary low-pass filter as shown in FIG. This resonant frequency _p is made to approximately match the fluctuating component frequency of the input signal. The response frequency of the system when the loop is closed is determined by the gain intersection frequency _o . Now, when an abnormality as shown in FIG. 4a appears in the output of the phase comparator 1, the phase abnormality detector 52 detects the abnormality, and this output opens the loop switch 51 during the abnormal section to disconnect the loop. Since the resonance of the system in open loop is _p of the resonant circuit 53, the output of the co-progressor circuit 53 changes exactly in accordance with the fluctuating component frequency of the input signal. Therefore, the output of the resonant circuit 53 changes as shown by the curve 44 in FIG.

Next, FIG. 4b shows the operation when an abnormality that lasts for an extremely long time appears in the output of the phase comparator 1. Even in such a case, since the resonant frequency of the resonant circuit 53 matches the fluctuating component frequency of the input component, the output of the voltage controlled oscillator 3 changes in the same way as in the case where there is almost no flaw.

On the other hand, when simply maintaining the state before the abnormality, the abnormal section is simply interpolated linearly, and it is not possible to interpolate sinusoidally with respect to the fluctuating frequency as in the present invention.

FIG. 7 is a block diagram showing another embodiment of the present invention. In FIG. 7, parts similar to those explained in FIG. 4 are designated by the same reference numerals.
In FIG. 7, a resonant circuit 5 consisting of a first-order low-pass filter 61 and a second-order band-pass filter 62 connected in cascade instead of the resonant circuit 53 of FIG.
3' is used. A curve 81 in FIG. 8 is the characteristic of the first-order low-pass filter 61, and a curve 82 is the characteristic of the second-order low-pass filter 61.
The following are the characteristics of the resonant circuit. If the resonant frequency of this secondary bandpass filter is matched to the frequency of the fluctuating component of the input signal, the operation will be similar to that shown in FIG. 6.

Effects of the Invention As described above, the present invention has a very simple configuration, and is capable of making the oscillation frequency follow the fluctuating frequency components of the input signal extremely accurately even during an extremely long-term abnormality. be.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing one side of a conventional PLL circuit, Figure 2 is its amplification versus frequency characteristic diagram, and Figure 3 is a diagram showing one side of a conventional PLL circuit.
5 and 4 are waveform diagrams for explaining the operation of the PLL circuit shown in FIG. 1, FIG. 5 is a block diagram showing an embodiment of the present invention, and FIG. FIG. 7 is a block diagram of another embodiment of the present invention, and FIG. 8 is a gain versus frequency characteristic diagram of the embodiment of FIG. 1... Phase comparator, 3... Voltage controlled oscillator,
51...Loop switch, 52...Phase abnormality detector, 53, 53'...Resonance circuit.

Claims (1)

[Claims] 1. A phase comparator that compares the phases of an input signal and an output signal, a phase abnormality detector that detects a change of a predetermined level or more in the output signal of the phase comparator, and a loop connected to the output side of the phase comparator. a resonant circuit connected to the output side of the loop switch, the resonant circuit having resonance whose resonant frequency almost matches the fluctuating component frequency of the input frequency and having the characteristics of a low-pass filter; 1. A phase lock loop circuit comprising: an oscillator whose frequency is controlled.