JPH02238716A - Phase locked loop oscillating circuit - Google Patents

Abstract

PURPOSE:To surely backup a subsystem by detecting it when no input signal is inputted due to a fault of a main oscillating circuit, interrupting a feedback loop via a changeover circuit and supplying a reference voltage to a voltage controlled oscillator from a reference voltage generating circuit. CONSTITUTION:When no input signal is inputted due to a fault of a main oscillating circuit 3, it is detected by an input signal detection circuit 24 to activate a changeover circuit 21 and to stop the operation of a charge pump 25 thereby throwing a switch means 48 to the position of a reference voltage generating circuit 48 and interrupting a feedback loop. Since the reference voltage generating circuit 48 applies a prescribed reference voltage to a voltage controlled oscillator 51 in this case, the voltage controlled oscillator 51 is oscillated at frequency controlled by the prescribed reference voltage and an output signal of a prescribed frequency is obtained. Thus, the subsystem 2 is able to be operated continuously and sufficient backup is attained.

Description

[Detailed Description of the Invention] [Summary] Regarding phase-locked oscillation circuits used in measuring instruments, magnetic recording devices, etc., the present invention relates to phase-locked oscillation circuits that can oscillate at a predetermined frequency even when there is no input signal due to a failure of the main oscillation circuit. The purpose of the circuit is to provide a phase comparator that compares the phases of input signals and outputs a phase difference signal, a charge pump that outputs a control signal according to the phase difference, and a charge pump that outputs a control signal according to the phase difference. a low-pass filter that outputs a voltage; a reference voltage generation circuit that generates a reference voltage; a voltage control generator that generates a signal of a predetermined frequency using the output from the low-pass filter or the reference voltage; switch means capable of switching to a reference voltage generation circuit; an input signal detection circuit for detecting an input signal; and a switch for switching a signal such that when there is no input signal, the switch means switches to the reference voltage generation circuit and disconnects the feedback loop. It consists of a circuit.

[Industrial Application Field] The present invention relates to a phase synchronized oscillation circuit used in measuring instruments, magnetic recording devices, and the like.

In recent years, phase-locked oscillation circuits have been used for backup systems for the purpose of duplicating oscillation circuits.

Therefore, under normal conditions, the main system and subsystem operate synchronously using the phase-locked oscillator circuit, but if a failure occurs in the main oscillator circuit, it is necessary to continue the operation of the subsystem through free-running oscillation of the phase-locked oscillator circuit. be.

[Prior Art] A phase-locked initiation circuit is used for a backup system as shown in FIG.

In FIG. 3, a subsystem (backup system) 2 is provided to back up the main system 1, and in the case of normal operation, the phase synchronized oscillation circuit (
PLL) 4 causes the subsystems 2 to operate synchronously.

As shown in FIG. 4, this phase synchronized oscillation circuit 4 includes a phase comparator 5, a charge pump 6, and a low-pass filter 7.
and a voltage-controlled generator 8, and the output signal fo of the voltage-controlled generator 8 is fed back to the phase comparator 5.

The relationship between the input signal fi and the output signal fO of the phase-locked oscillator circuit 4 is shown in FIG.
The relationship between CO and the output signal fo is shown in FIG.

As is clear from FIGS. 5 and 6, the output signal fo
detects the phase so as to follow the input signal fi within a certain frequency range A, controls the voltage vCO of the voltage control generator 8, and outputs the voltage vCO from the voltage control generator 8.

[Problems to be Solved by the Invention] As mentioned above, when using a phase-locked oscillator circuit for the purpose of duplicating the ignition circuit, it is possible that the input signal fi is completely input to the phase-locked oscillator circuit due to a failure of the main oscillation circuit. In order to maintain the performance of the subsystem during backup, it is desirable that the output signal fO be oscillated at the center frequency fc.

However, in such a conventional phase-locked oscillator circuit, as shown in FIG. 6, the control voltage ■CO changes infinitely to point a when trying to synchronize with the input signal fi, and the input signal f When oscillating at a free-running oscillation number fs, the frequency deviates greatly from the center frequency fc. As a result, a situation may arise in which the operation of the subsystem cannot be continued, resulting in the problem that sufficient backup cannot be performed.

The present invention has been made in view of such conventional problems, and provides a phase synchronized starting circuit that can be activated at a predetermined frequency even when there is no input signal due to a failure of the main oscillation circuit. It is intended to.

[Means to solve the problem] FIG. 1 is a basic configuration diagram of the present invention.

In FIG. 1, 11 is a phase comparator that compares the phases of input signals and outputs a phase difference signal, 25 is a charge pump that outputs a control signal according to the phase difference, and 40 is a predetermined phase difference voltage according to the control signal. a low-pass filter that outputs 48
51 is a voltage controlled oscillator that oscillates a signal of a predetermined frequency based on the output from the low-pass filter 40 or the reference voltage; 46 is a circuit from the low-pass filter 40 to the reference voltage generating circuit 48;
24 is an input signal detection circuit that detects an input signal; 21 is a switch that switches the signal so that when there is no input signal, the switch means 46 switches to the reference voltage generation circuit 48 to break the feedback loop; It is a circuit.

[Function] In the present invention, when an input signal is not input due to a failure in the main starting circuit, this is detected by the input signal detection circuit, the switching circuit is operated, and the operation of the charge pump is stopped. The switch means is switched to the reference voltage generation circuit to disconnect the feedback loop. At this time,
Since the reference voltage generation circuit supplies a predetermined reference voltage to the voltage controlled oscillator, the voltage controlled oscillator is activated at a frequency controlled by the predetermined reference voltage, and an output signal of a predetermined frequency is obtained.

Therefore, the subsystem can continue to operate and sufficient backup can be performed.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention.

First, to explain the configuration, in FIG. 2, reference numeral 11 is a phase comparator that compares the phase of the input signal fi, and the phase comparator 11 is composed of Nantes circuits 12 to 20.
The data of D1 is output to the switching circuit 21.

The switching circuit 21 is composed of Nantes circuits 22 and 23, and when the output signal 01 from the input signal detection circuit 24 is at H level, that is, when there is an input signal fi, the data of U1 and D1 from the phase comparator 11 is transferred to the charge pump. Output to 25,
When the output signal 01 from the input signal detection circuit 24 is at the L level, that is, when there is no input signal fi, the output signal 02 is fixed at the "]" level.

The input signal detection circuit 24 is composed of a resistor 26, a capacitor 27, and a comparator 28, and switches between an H level output signal 01 when there is an input signal fi and an L level output signal 01 when there is no input signal fi. Output to circuit 21.

Charge pump 25 includes transistors 29 to 35 and resistor 3
6 to 39, and control signals UF. Output DF.

40 is a low-pass filter to which control signals UF and DF from the charge bomb 25 are input;
0 has capacitor 41 and resistor 42, resistor 43.44
, a FET transistor 45, and an output stage transistor (switch means) 46 are connected. When the charge pump 25 stops operating, the output stage transistor 4
6 is turned off, the output of the low-pass filter 40 is in an open state, and the feedback loop is cut off.
During normal operation of the charge pump 25, a phase difference voltage 03 is output.

Note that the phase comparator 11, charge pump 25, and output stage transistor 46 collectively constitute one IC 47 (MC4044 manufactured by Motorola).

Reference numeral 48 denotes a reference voltage generation circuit consisting of a resistor 49 and a resistor 50. When the output stage transistor 46 is turned off and the output of the low-pass filter 40 is in an open state, the divided voltage of the resistor 49.50 is generated under voltage control. output to the pregnancy device 51. The voltage control generator 51 is a reference voltage generating circuit 4B.
It will be free-running at a frequency controlled by the divided voltage from.

Next, the operation will be explained.

First, a case where the input signal fi is input will be explained.

When the input signal fi is being input, the input signal fi is detected by the input signal detection circuit 24, and its output signal 01 becomes H level. Therefore, U from the phase comparator 11
1. The data of D1 passes through the switching circuit 21 and is input to the charge pump 25.

Control signal tJF. corresponding to the phase difference output from charge pump 25. DF passes through the low-pass filter 40 and is supplied to the voltage controlled oscillator 51 as a phase difference voltage 03, and the voltage controlled oscillator 51 generates an output signal fo synchronized with the input signal f.
Output. In this case, the output stage transistor 46 is in an on state, and the output stage transistor 46 and the voltage controlled oscillator 5 are connected to each other.
1, and the output signal f○ is fed back to the phase comparator 11.

Next, a case will be described in which the input signal fi is not input due to a failure in the main oscillation circuit 3.

When the input signal fi is not input, the input signal detection circuit 2
The output signal 01 of No. 4 becomes the L level, the switching circuit 21 is closed, and the output signal 02 thereof is fixed at the I level.

Therefore, charge pump 25 stops its operation.

Therefore, the output stage transistor 46 is in an off state, the output of the low pass filter 40 is in an open state, and the feedback loop is cut off.

At this time, the reference voltage generation circuit 48 supplies the divided voltage of the resistors 49 and 50 to the voltage controlled oscillator 51, so that the voltage controlled oscillator 51 becomes a divided voltage and runs freely at a controlled frequency. Therefore, an output signal fo@ of a predetermined frequency can be obtained.

Therefore, even if the main initiation circuit 3 fails, the subsystem 2 can continue to operate.

[Effects of the Invention] As explained above, according to the present invention, when the input signal is not input due to a failure in the main starting circuit, this is detected and the feedback loop is disconnected via the switching circuit. Since the reference voltage is supplied from the reference voltage generating circuit to the voltage controlled oscillator, an output signal of a predetermined frequency can be obtained, and the subsystem can be backed up reliably.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of the present invention; Fig. 2 is a diagram showing an embodiment of the present invention; Fig. 3 is a diagram showing duplication of the initiation circuit; Fig. 4 is a block diagram showing a conventional example; FIG. 5 is a graph showing the relationship between input signals and output signals, and FIG. 6 is a graph showing the relationship between output signals and control voltage. In the figure, 11... Phase comparator, 12-20... Nantes circuit, 21... Switching circuit, 22.23... Nantes circuit, 24... Input signal detection circuit, 25... Charge Pump, 26...Resistor, 27...Capacitor, 28...Comparator, 29-35...Transistor, 36-39...Resistor, 40...Low-pass filter, 41...Capacitor, 42...Resistor, 43.44...Resistor, 45...FET transistor, 46...Output stage transistor (switch means), 47
...IC, 48...Reference voltage generation circuit, 49.50...Resistor, 51...Voltage control generator.

Claims (1)

[Claims] A phase comparator (11) that compares the phases of input signals and outputs a phase difference signal; a charge pump (25) that outputs a control signal according to the phase difference; and a charge pump (25) that outputs a predetermined phase difference voltage based on the control signal. a low-pass filter (40), a reference voltage generation circuit (48) that generates a reference voltage, and a voltage-controlled oscillator (51) that oscillates a signal at a predetermined frequency using the output from the low-pass filter (40) or the reference voltage; switch means (46) capable of switching from the low-pass filter (40) to the reference voltage generation circuit (48);
an input signal detection circuit (24) for detecting an input signal; and a switching circuit (21) for switching the signal so that when there is no input signal, the switching means (46) switches to the reference voltage generation circuit (48) and disconnects the feedback loop. )and,
A phase synchronized oscillation circuit characterized by comprising: