JPH07240684A - Phase locked loop circuit - Google Patents

Abstract

PURPOSE:To obtain a highly stable self-running frequency by applying temperature compensation to the self-running frequency control for a PLL circuit. CONSTITUTION:When an input signal 11 is interrupted, an output of an interrupt detection circuit 5 is inverted and a selector 6 selects an output of a variable delay circuit 7 whose delay is controlled by an output of a memory 8. An output of a phase comparator 1 is a pulse having a duty ratio proportional to the delay of the variable delay circuit 7, the pulse is smoothed by a filter 2 to be a control input voltage of a voltage controlled oscillator 3. A temperature detection circuit 9 detects a change in an ambient temperature and temperature compensation data corresponding to its output are outputted to the memory 8 and its output controls a delay in the variable delay circuit 7 to control a control input voltage of the voltage controlled oscillator 3. Thus, the temperature compensation for the self-running frequency is realized by storing the temperature compensation data to the memory 8 in advance.

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 (PLL) circuit which is used in various transmission and communication devices and which outputs an oscillation signal synchronized with a reference signal.

[0002]

2. Description of the Related Art An example of a conventional phase locked loop circuit is shown in FIG. The input signal 11 is input to the first comparator input terminal of the phase comparator 1 connected to the phase locked loop circuit input terminal. This input signal 11 is phase-compared by the frequency-divided output 12 of the frequency-dividing circuit 4 input to the second comparator input terminal of the phase comparator 1 by the phase comparator 1, and the result is compared with the phase difference between the two. It is output as a PWM wave. This PWM wave is filtered by the filter 2 and becomes the control input of the voltage controlled oscillator 3. The output frequency of the voltage controlled oscillator 3 changes according to the voltage value of its control input. The output of the voltage controlled oscillator 3 is frequency-divided by the frequency dividing circuit 4 to a frequency equal to that of the input signal 11 and applied to the second comparator input terminal of the phase comparator 1. The phase locked loop output signal is taken out from the output terminal of the voltage controlled oscillator 3.

The above phase-locked loop circuit constitutes a kind of servo system, and in the steady state, the phase comparator 1
The phase difference between the two inputs is constant and their frequencies match. Therefore, this circuit constitutes a circuit that multiplies the frequency of the input signal 11 by the frequency division ratio of the frequency dividing circuit 4.

[0004]

When the phase-locked loop circuit is actually used, even when the input signal 11 is disconnected, the phase-locked loop circuit is self-propelled at a frequency as close as possible to the output frequency in the steady state before that. Often things are required. In the example of FIG. 1, when the input signal 11 is cut off, the output of the phase comparator 1 can only output a pulse having a certain duty ratio. How much the duty ratio is set depends on the circuit configuration of the phase comparator 1.

The pulse having the constant duty ratio is smoothed by the filter 2 and input to the voltage controlled oscillator 3 as a constant DC voltage. Normally, it is desirable to set the DC voltage so that the input signal 11 matches the control input voltage value of the voltage controlled oscillator 3 in the steady state before the disconnection, and a pulse having a duty ratio corresponding thereto is set at the time of free running. The phase comparator 1 is designed to output.

On the other hand, the voltage controlled oscillator 3 has a frequency-temperature characteristic, and even if it keeps applying a constant control input voltage, its output frequency changes due to a change in ambient temperature. . For this reason, even if the above-mentioned control of the phase-locked loop circuit self-running is performed, the output frequency changes with the change of the ambient temperature, so that it deviates from the expected steady-state output frequency. Had a point.

Therefore, an object of the present invention is to provide a phase-locked loop circuit having a structure that, even when an input signal is cut off, it is free-running at a frequency close to the output frequency in the previous steady state.

Another object of the present invention is that, when the input signal is cut off, it automatically becomes a free-running state at a frequency close to the output frequency in the previous steady state, and the input signal comes again. At times, it is to provide a phase-locked loop circuit that automatically outputs an oscillation signal synchronized with an input signal and becomes a steady state.

[0009]

According to the present invention, there are provided a phase locked loop circuit input terminal for receiving an input signal, a phase comparator having first and second comparator input terminals, and a voltage controlled oscillator, A phase-locked loop circuit that comprises a phase-locked loop including the second comparator input terminal, the phase comparator, and the voltage-controlled oscillator, and extracts a phase-locked loop output signal from the output terminal of the voltage-controlled oscillator. A disconnection detection circuit connected to the phase-locked loop circuit input terminal for detecting disconnection of the input signal and outputting a disconnection detection signal; and first and second selector input terminals and a selector output terminal. The first selector input terminal is connected to the phase-locked loop circuit input terminal, and the selector output terminal is the first comparator Is connected to the force terminal, when the loss detection circuit does not output the disconnection detection signal, the first
Connect the selector input terminal of to the selector output terminal,
When the disconnection detection circuit is outputting the disconnection detection signal,
A selector that connects the second selector input terminal to the selector output terminal; a temperature detection circuit that detects an ambient temperature and outputs a digital temperature signal that represents the detected temperature; and a temperature compensation that corresponds to the detected temperature in advance. A memory that stores data and outputs temperature compensation data corresponding to the detected temperature represented by the digital temperature signal in response to the digital temperature signal; a delay circuit input terminal and a delay circuit output terminal A control input terminal, the delay circuit input terminal is connected to the second comparator input terminal, the delay circuit output terminal is connected to the second selector input terminal, and the control input terminal is the memory. A variable delay circuit that is connected to the output of the delay circuit, applies a delay corresponding to the output of the memory to the signal of the delay circuit input terminal, and outputs the delayed signal to the delay circuit output terminal. Phase locked loop circuit is obtained, characterized in that it comprises.

Further in accordance with the invention, the phase locked loop filters the output of the phase comparator in addition to the second comparator input terminal, the phase comparator and the voltage controlled oscillator. And a filter for applying the filtered output to the input terminal of the voltage controlled oscillator, and a frequency divider for dividing the signal from the output terminal of the voltage controlled oscillator and applying the divided output to the second selector input terminal. A phase-locked loop circuit is obtained which is characterized in that

[0011]

Embodiments of the present invention will now be described with reference to the drawings. Referring to FIG. 1, in a phase locked loop circuit according to an embodiment of the present invention, in a normal state (when the input signal 11 is not broken), the selector 6 operates as shown in FIG.
The first selector input terminal connected to the phase locked loop circuit input terminal receiving
It is connected to the selector output terminal which is connected to the comparator input terminal. At this time, since the variable delay circuit 7, the memory 8 and the temperature detection circuit 9 are separated from the phase locked loop circuit, the operation of the phase locked loop circuit becomes equal to that of the conventional example described above.

On the other hand, temperature compensation data is written in advance in the memory 8 whose address is the output of the temperature detection circuit 9, and the data corresponding to the output of the temperature detection circuit 9 is given as a control input of the variable delay circuit 7. To be As a result, the input / output delay difference of the variable delay circuit 7 is controlled by the temperature compensation data written in the memory 8.

When the input signal 11 is disconnected, the disconnection detection circuit 5
Outputs a disconnection detection signal (an inverted signal of the output signal when the input signal 11 is not disconnected), the selector 6 is connected to the output of the variable delay circuit 7 as shown by the broken line in FIG.
The selector input terminal of is switched so as to be connected to the selector output terminal. As a result, the phase comparator 1 comes to output a pulse having a duty ratio corresponding to the phase difference (in other words, delay difference) between the input and output of the variable delay circuit 7.
Further, this duty ratio is converted into a specific voltage value of the control input of the voltage controlled oscillator 3 as described above.

The temperature compensation of the free-running frequency of the phase-locked loop circuit is performed using the above mechanism.
This is a feature of the present invention. That is, the temperature compensation controls the duty ratio of the output of the phase comparator 1 by controlling the delay amount of the variable delay circuit 7, and thereby the control input voltage of the voltage controlled oscillator 3 is controlled, and as a result, the output frequency is changed. It is realized by utilizing the fact that it is controlled.

Time charts of input and output of the phase comparator 1 are shown in FIGS. 3 and 4 assuming two cases where the ambient temperatures are different. The phase comparator 1 outputs "1" from the rising edge of the signal 12 which is one input to the rising edge of the signal 13 which is the other input, and outputs "0" in the other cases. Output signal 14 of comparator 1
Indicated by. Comparing FIG. 3 and FIG. 4, comparing the variable delay circuit 7
There is a difference in the phase of the signal 13 which is the output of the above because it is assumed that the ambient temperature is different in each figure as described above. Therefore, the temperature compensation control amount applied to the variable delay circuit 7 is increased. Is different, and the delay amount of the variable delay circuit 7 is different. As a result, it can be seen that there is a difference in the duty ratio of the output signal 14 of the phase comparator 1 in FIGS. 3 and 4. The waveform of the output signal 14 after passing through the filter 2 is shown by a wavy line. In both cases of FIG. 3 and FIG. 4, the pulse component of the signal 14 is sufficiently suppressed by the filter 2 and the voltage value becomes a constant voltage value proportional to the duty ratio of the signal 14. This voltage value becomes the control input voltage of the voltage controlled oscillator 3. Regarding the duty ratio of the signal 14, the width of “1” in the case of FIG. 3 is wider than that in the case of FIG. 4, so a higher control voltage is applied to the voltage controlled oscillator 3.

In the above description, controlling the delay amount of the variable delay circuit 7 by the temperature compensation control controls the control input voltage of the voltage controlled oscillator 3, and the process of controlling the output frequency is understood. You can do it.

[0017]

As described above, according to the present invention, temperature compensation can be applied to the free-running frequency control of the phase-locked loop circuit. Therefore, even when the phase-locked loop circuit is free-running, a normal input is applied. It has an excellent effect that a highly stable output frequency close to a steady state output frequency can be obtained. By using the present invention, the phase-locked loop circuit can supply accurate timing even when it is free-running, so that it is possible to accurately transmit data even when the input of the phase-locked loop circuit is disconnected in an emergency. The effect that the bit error rate is reduced and the line quality is improved can be expected.

Further, according to the present invention, since the disconnection detection circuit and the selector connected to the disconnection detection circuit are provided, when the input signal is disconnected, the output frequency of the previous steady state is automatically set. A phase-locked loop circuit can be obtained which becomes a free-running state at a close frequency and automatically outputs an oscillation signal synchronized with the input signal again when the input signal arrives again.

[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 example.

FIG. 3 is a time chart showing an example of the input / output relationship of the phase comparator.

FIG. 4 is a time chart showing another example of the input / output relationship of the phase comparator.

[Explanation of symbols]

 1 phase comparator 2 filter 3 voltage controlled oscillator 4 frequency divider circuit 5 disconnection detection circuit 6 selector 7 variable delay circuit 8 memory 9 temperature detection circuit 11 input signal

Claims (2)

[Claims] 1. A phase-locked loop circuit input terminal for receiving an input signal, a phase comparator having first and second comparator input terminals, and a voltage-controlled oscillator, the second comparator input terminal. In the phase-locked loop circuit that forms a phase-locked loop with the phase comparator and the voltage-controlled oscillator, and extracts a phase-locked loop output signal from the output terminal of the voltage-controlled oscillator, the phase-locked loop circuit Connected,
A disconnection detection circuit that detects disconnection of the input signal and outputs a disconnection detection signal; and first and second selector input terminals and a selector output terminal, wherein the first selector input terminal is the phase-locked loop When the disconnection detection circuit is connected to a circuit input terminal, the selector output terminal is connected to the first comparator input terminal, and the disconnection detection circuit does not output the disconnection detection signal, the first selector input terminal is connected to the circuit. A selector connected to the selector output terminal and connecting the second selector input terminal to the selector output terminal when the disconnection detection circuit outputs the disconnection detection signal; A temperature detection circuit for outputting a digital temperature signal indicating the temperature compensation data; temperature compensation data corresponding to the detected temperature is stored in advance, and the digital temperature signal corresponding to the detected temperature is stored in advance. A memory for outputting temperature compensation data corresponding to the detected temperature represented by a temperature signal; a delay circuit input terminal, a delay circuit output terminal, and a control input terminal, wherein the delay circuit input terminal is the second The delay circuit output terminal is connected to the comparator input terminal, the delay circuit output terminal is connected to the second selector input terminal, the control input terminal is connected to the output of the memory, and the signal of the delay circuit input terminal is connected to the signal of the memory. And a variable delay circuit which gives a delay corresponding to the output and outputs the delayed signal to the output terminal of the delay circuit. 2. The phase-locked loop filters the output of the phase comparator in addition to the second comparator input terminal, the phase comparator and the voltage controlled oscillator, and outputs the filtered output. Is provided to the input terminal of the voltage controlled oscillator, and a frequency divider that divides the signal from the output terminal of the voltage controlled oscillator and applies the divided output to the second selector input terminal. The phase-locked loop circuit according to claim 1, wherein: