JPH04122126A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To prevent the synchronizing step-out signal at the application of power by starting application of a power supply voltage to each section of a phase locked loop when the output signal of an oscillator reaches a prescribed level. CONSTITUTION:A power supply voltage from a power supply 6 is fed to an oscillator 1 and a frequency divider 2 and the output signal of the oscillator 1 is inputted to the frequency divider 2 and a level detector 7. The level detector 7 outputs an output signal when an output signal from the oscillator 1 reaches a prescribed level P1 to close the connection of a switch 8 connecting the power supply 6, a voltage controlled oscillator 4 and a frequency divider 5. A power supply voltage V0 is fed to the frequency divider 5 and the voltage controlled oscillator 4 accordingly and the frequency divider 5 divides the output signal from the voltage controlled oscillator 4 and the resulting signal is inputted to a phase comparator 3 together with an output signal from the frequency divider 2 and the operation of the phase locked loop is started so as to control the oscillating frequency of the voltage controlled oscillator 4 in response to a phase difference of both the frequency division signals. Thus the output of the synchronizing step-out signal is prevented in a transient state at the application of power.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a frequency conversion circuit.

[Conventional technology]

As shown in FIG. 3, the conventional frequency conversion circuit includes an oscillator 1, a frequency divider 2 that divides the output signal of the oscillator, and a signal obtained by dividing the output signal of the voltage controlled oscillator 4 by the frequency divider 2. Frequency divider 1
It has a phase comparator 3 that detects a phase difference with the frequency-divided signal of ing.

[Problem to be solved by the invention]

In this conventional frequency conversion circuit, since the power supply voltage is applied to the oscillator 1 and the voltage-controlled oscillator 4 at the same time, an out-of-synchronization signal is output from the voltage-controlled oscillator 4 in a transient state from when the power is turned on until it stabilizes. There is a problem.

[Means to solve the problem]

The frequency conversion circuit of the present invention includes an oscillation circuit having an oscillator and a first frequency divider that divides the output signal of the oscillator, a voltage controlled oscillator, and a second frequency divider that divides the output signal of the voltage controlled oscillator.
and a phase comparator that generates a voltage signal for controlling the oscillation frequency of the voltage controlled oscillator in response to a phase difference between the divided signals of the first and second frequency dividers. a level detector that generates a switching control signal when the output signal of the oscillator reaches a preset level; and a power supply connected to the oscillation circuit and for supplying the phase-locked loop. A power source that emits voltage,
A switch is provided in the middle of a power supply line from the power source to the phase locked loop, and switches the connection of the power supply line to an on state in response to the switching control signal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG.
) to (c) are signal waveform diagrams showing the operation of this embodiment.

A power supply voltage from a power supply 6 is supplied to an oscillator 1 and a frequency divider 2, and an output signal of the oscillator 1 is input to a frequency divider 2 and a level detector 7. The level detector 7 outputs an output signal when the output signal of the oscillator 1 reaches a certain level P1, and turns on the connection of the switch 8 that connects the power supply 6, the voltage-controlled oscillator 4, and the frequency divider 5. Switch to Accordingly, the power supply voltage Vo is supplied to the frequency divider 5 and the voltage controlled oscillator 4, and the frequency of the output signal from the voltage controlled oscillator 4 is divided by the frequency divider 5, and the phase is compared with the output signal from the frequency divider 2. The phase-locked loop starts operating to control the oscillation frequency of the voltage-controlled oscillator 4 according to the phase difference between the two frequency-divided signals.

Therefore, in this embodiment, when the output signal of the oscillator 1 reaches a certain level and stabilizes, the power supply voltage supply to the phase-locked loop is started, and an out-of-synchronization signal is output during the transient state when the power is turned on. can be prevented.

〔Effect of the invention〕

As explained above, the present invention has the effect of eliminating out-of-synchronization output when the power is turned on by starting supplying power supply voltage to each part of the phase-locked loop when the output signal of the oscillator reaches a certain level. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2(a) to (
c) is a signal waveform diagram in an embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional frequency conversion circuit. 1... Oscillator, 2, 5... Frequency divider, 3... Phase comparator, 4... Voltage controlled oscillator, 6... Power supply, 7...
・Level detector, 8...switch.

Claims (1)

[Claims] an oscillation circuit having an oscillator and a first frequency divider that frequency-divides an output signal of the oscillator; a voltage-controlled oscillator; a second frequency divider that frequency-divides the output signal of the voltage-controlled oscillator; a phase-locked loop having a phase comparator for generating a voltage signal for controlling the oscillation frequency of the voltage-controlled oscillator in response to a phase difference between both frequency-divided signals of a second frequency divider; a level detector that generates a switching control signal when a preset level is reached; a power supply that is connected to the oscillation circuit and generates a power supply voltage to be supplied to the phase-locked loop; A frequency conversion circuit comprising: a switch that is interposed in the middle of a power supply line to the phase-locked loop and switches the connection of the power supply line to an on state in response to the switching control signal. .