JPH04200015A - Phase locked loop - Google Patents

Abstract

PURPOSE:To obtain an output with less spurious radiation and inexpensive circuit constitution by providing a DC/DC converter receiving a reference input signal of the phase locked loop as a switching signal to the phase locked loop and driving a charge pump with an output voltage of the DC/DC converter. CONSTITUTION:A characteristic of a low pass filter 4 is selected independently of a loop constant so as to reduce noise of a frequency component fref of a reference signal outputted from a comparator circuit 1. Since a DC/DC converter 7 uses a reference input signal of the loop as a switching signal, the switching frequency is fref and noise reduction effect by the low pass filter 4 is attained for an output voltage of the DC/DC converter 7 and an output with less spurious radiation is obtained. Thus, a filter to reduce the frequency component of a switching signal of the DC/DC converter is not required as separate provision and the output with less spurious radiation is obtained with inexpensive loop circuit constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a phase-locked loop (PLL), and more particularly to an improvement in a control power supply for a voltage-controlled oscillator (VCO).

<Prior Art> FIG. 3 is a circuit diagram of a general phase-locked loop. In the figure, 1 is a phase comparator, and one input terminal has a frequency f2. ．． A reference input signal is applied. 2 is a charge pump that amplifies the output of the phase comparator 1,
The output signal of the phase comparator 1 is applied, and the driving voltage from the power supply circuit 3 is also applied. 4 is a low-pass filter, which is connected to the output terminal of the charge pump 2. 5 is a voltage controlled oscillator (VCO), which is connected to the output terminal of the filter 4. 6 is a frequency divider;
The input terminal is connected to the output terminal of the voltage controlled oscillator 5, and the output terminal is connected to the other input terminal of the phase comparator 1.

In a circuit with such a configuration, in order to widen the output frequency range, it is necessary to widen the variable range of the frequency of the voltage controlled oscillator 5 (indicated by ``■''), and the voltage applied from the power supply circuit 3 to the charge pump 2 must be approximately 30V. Is it necessary to make it higher than other circuits?

<Problem to be solved by the invention> However, when trying to realize such a power supply circuit 3 with a DC/DC converter, a powerful converter is required to prevent the switching noise from affecting the output signal. Countermeasures such as installing a filter must be taken, which raises the problem of increased costs.

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above points, and is to realize a phase-locked loop that can provide an output with a wide output frequency range and less spurious with an inexpensive circuit configuration.

Means for Solving the Problems> The present invention to solve the above problems includes: In a phase-locked loop including a charge pump in the loop, a DC/DC converter whose switching signal is a reference input signal of the phase-locked loop is provided, The charge pump is characterized in that the charge pump is driven by the output voltage of the DC/DC converter.

Effect> Generally, in a phase-locked loop, a low-pass filter that is unrelated to the loop constant is used to reduce noise at the reference signal frequency that appears in the output signal of the phase comparator.

In the present invention, since the reference input signal of the loop is used as the switching signal of the DC/DC converter, the noise reduction effect of the filter can also be obtained for the output voltage of the DC/DC converter.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a principle circuit diagram of a phase-locked loop according to the present invention, and parts common to those in FIG. 3 are given the same numbers and their explanations will be omitted. In the figure, 7 is a switching type DC/DC converter. The DC/DC converter 7 receives frequency f71. as a switching signal. The reference input signal of the loop is used. The DC/DC converter 7 outputs a voltage of about 30 V, which is higher than other circuits, and the output voltage is applied to the charge pump 2.

In such a configuration, the characteristics of the low-pass filter 4 are the frequency components of the reference signal output from the phase comparator 1.
It is chosen independently of the loop constant to reduce tel noise. Since the DC/DC converter 7 used in the present invention also uses the loop reference input signal as the switching signal, the switching frequency is f7.1.
The output voltage of the DC/DC converter 7 also has a noise reduction effect due to the low-pass filter 4, and an output with less spurious is obtained.

FIG. 2 is a circuit diagram of an embodiment of a phase-locked loop according to the present invention, and parts common to those in FIG. 1 are given the same numbers and their explanation will be omitted. In the figure, the frequency of the reference input signal is 1. It is set to MHz. DC/
+30V is applied from the DC converter 7. The filter 4 has a cutoff frequency f of 300 KHz.
A low-pass filter (additional filter) 41 and a notch filter 42 having a steep attenuation characteristic with respect to IMHz are connected in series.

A frequency divider 6 having a frequency division ratio set to 1/100 to 1/200 is used.

With such a circuit configuration, the voltage controlled oscillator 5
output frequency to 100MHz with IMHz frequency resolution
It can be varied from 200MHz to 200MHz.

Note that the specific numerical values are not limited to those in the embodiments, and may be set to appropriate values depending on the purpose.

<Effects of the Invention> As described above in detail, the present invention has the following effects.

Since the reference input signal of the loop is used as the switching signal of the DC/DC converter, it is possible to utilize the noise reduction effect of the filter provided to reduce the noise component of the reference signal of the loop, and the switching signal of the DC/DC converter can be used. It is possible to obtain an output with less spurious through an inexpensive loop circuit structure without separately providing a filter for reducing the frequency components of.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the principle of a phase-locked loop according to the present invention, FIG. 2 is a circuit diagram showing an embodiment of a phase-locked loop according to the present invention, and FIG. 3 is a circuit diagram showing an example of a conventional phase-locked loop. It is a diagram.

Claims (1)

[Claims] In a phase-locked loop including a charge pump in the loop, a DC/DC converter is provided that uses a reference input signal of the phase-locked loop as a switching signal, and the charge pump is connected to an output voltage of the DC/DC converter. A phase-locked loop characterized by being driven by.