JPH02113627A - Phase synchronizing oscillator - Google Patents

Abstract

PURPOSE:To decrease an offsetting voltage fluctuation and to attain the stable oscillation by providing an automatic level control circuit between the output of a voltage control oscillator and the input of a phase comparator. CONSTITUTION:The title oscillator has a voltage control oscillator 1 to respond to a control signal, a reference signal source 3, a phase comparator 2 to compare the voltage control oscillator with the output phase of the reference signal source 3 and a loop filter 4 to filter the output of the phase comparator 2 and generate the control voltage. An automatic level control circuit 5 is provided between the output of the voltage control oscillator 1 and the input of the phase comparator 2. Consequently, the input level from the voltage control oscillator 1 to the phase comparator 2 is automatically controlled, held to a constant value, and the output level fluctuation of the voltage control oscillator 1, namely, the input level fluctuation to the phase comparator 2 can be eliminated. Thus, the offsetting voltage fluctuation is decreased, the phase synchronization is more stably maintained and the stable oscillation can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an analog type phase-locked oscillator, and particularly to a highly stable phase-locked oscillator.

[Conventional technology]

Conventionally, this type of analog phase synchronized oscillator has been used to directly connect one output from a voltage controlled oscillator (VCO) 1 to a phase comparator (sampling) and an aids detector 5 as shown in FIG.
PD) 2 and compares the phase with the output from the reference signal source 3, and the output (error output) from the phase comparator 2 corresponding to these phase errors is filtered by the loop filter 4 and output from the voltage controlled oscillator 1. It is configured to be applied to a frequency control voltage input terminal.

[Problems to be Solved by the Invention] In the conventional analog type phase-locked oscillator described above, even when the phase error is zero, the unbalance in the phase comparator 2 causes an imbalance in the operational amplifier in the loop filter even when the error output is zero. Due to such imperfections, a non-zero voltage is input to the frequency control voltage input terminal of the voltage control oscillator 1. As a result, the system exhibits phase comparison characteristics within a control voltage range (hold-in range) that is unique to the system and within which phase synchronization can be maintained, using this voltage (offset voltage) as the reference center voltage.

This offset voltage fluctuates because the initial characteristics of the components change, particularly due to temperature fluctuations, and the output level of the voltage controlled oscillator input to the phase comparator is not constant. The fourth graph shows a typical example of this situation.
It is a diagram. In the figure, the input level fluctuation of the phase comparator (ΔP
Offset voltage variation (ΔVoFF) with respect to vco)
It shows.

If this offset voltage variation exceeds the hold-in range, phase synchronization will occur. Therefore, in order to maintain the phase synchronization of the system, it is necessary to suppress the offset voltage fluctuation by G below the value specified by the hold-in range, etc., but one of the biggest causes of offset voltage fluctuation is the phase There is a problem in that fluctuations in the input level of the comparator, that is, the output level of the voltage controlled oscillator, cannot be avoided due to temperature changes and other internal and external factors that are difficult to predict.

An object of the present invention is to provide a phase-locked oscillator that reduces offset voltage fluctuations and enables stable oscillation.

[Means to solve the problem]

The phase-locked oscillator of the present invention includes a voltage-controlled oscillator that responds to a control signal, a reference signal source, a phase comparator that compares the output phases of the voltage-controlled oscillator and the reference signal source, and a filter that filters the output of the phase comparator. and a loop filter for generating the control voltage, and further includes an automatic loop filter provided between the output of the voltage controlled oscillator and the input of the phase comparator. i1
It has one circuit.

[Effect]

In a serial configuration, the input level from the voltage controlled oscillator to the phase comparator is automatically controlled and maintained at a fixed level, eliminating fluctuations in the output level of the voltage controlled oscillator, that is, fluctuations in the input level to the phase comparator. Offseno] - Reduces voltage fluctuations.

〔Example] Next, the present invention will be explained with reference to the drawings L2.

FIG. 1 shows a block diagram of the present invention. In the figure,
1 is a voltage controlled oscillator, 2 is a phase comparator, 3 is a reference signal source, and 4 is a loop filter, which together constitute a phase synchronized oscillator. An automatic level control circuit (AI, C) 5 is connected between the voltage controlled oscillator 1 and the phase comparator 2 to keep the input signal level of the phase comparator 2 generated from the voltage controlled oscillator 1 constant. . A signal serving as a reference for phase comparison is inputted to the phase comparator 2 from a reference signal source 3.
The output of the phase comparator 2 is filtered by a loop filter 4 and fed back to the voltage controlled oscillator 1.

FIG. 2 is a block diagram showing the configuration of FIG. 1 in more detail, in which the automatic level control circuit 5 shown in FIG. (PIN ATT)8. That is, the signal going from the voltage controlled oscillator 1 to the phase comparator 2 is
PTN so that the input level at level detector 6 is constant.
Controlled by a diode attenuator 8.

According to this configuration, from the voltage controlled oscillator 1 to the phase comparator 2
The level of the signal input to is automatically controlled by the automatic level control circuit 5 and held at a constant value. For this reason, fluctuations in the output level of the voltage controlled oscillator 1 that occur due to aging or temperature changes in the components, that is, fluctuations in the input level to the phase comparator 2, are eliminated, offset voltage fluctuations are reduced, and phase synchronization is maintained stably. Oscillation can be obtained [Effects of the Invention] As explained above, the present invention automatically controls the input level from the voltage controlled oscillator to the phase comparator and maintains it at a constant value. Level fluctuations, that is, input level fluctuations to the phase comparator can be eliminated, which has the effect of significantly reducing offset voltage fluctuations, maintaining phase synchronization more stably, and obtaining stable oscillation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an analog phase-locked oscillator according to the present invention, FIG. 2 is a block diagram specifically showing the configuration of FIG. 1, and FIG. 3 is a block diagram of a conventional analog phase-locked oscillator. Figure 4M is a graph showing offset voltage fluctuations with respect to input level fluctuations of the phase comparator. 1...Voltage controlled oscillator (VCO), 2...Phase comparator (SPD), 3...3 reference signal sources, 4...Loop filter, 5...Automatic level control circuit (DET) ,
6...Level detector (DET), 7...Amplifier, 8
...PIχ -180

Claims (1)

[Claims] 1. A voltage controlled oscillator that responds to a control signal, a reference signal source, a phase comparator that compares the output phases of the voltage controlled oscillator and the reference signal source, and filters the output of the phase comparator to detect the control signal. A phase-locked oscillator having a loop filter that generates a voltage-controlled oscillator, characterized in that an automatic level control circuit is provided between the output of the voltage-controlled oscillator and the input of the phase comparator.