JPH03280718A - Digital control frequency synthesizer - Google Patents

Abstract

PURPOSE:To reduce the control step by setting a frequency division with an external control signal or a digital-digital converter. CONSTITUTION:Frequency dividers 1, 2 frequency-divide an input signal f1 of an input terminal 10 to 1/N, 1/M by using a control signal of control terminals 18, 19. A frequency mixer 3 mixes an output frequency f1/N of the frequency divider 1 and an output frequency f0 of a voltage controlled oscillator 6, a phase comparator 5 compares the phase of the output frequency f1/N-f0 of a filter 4 with the phase of the output frequency f1/N of the frequency divider 2, outputs a frequency control signal of the voltage controlled oscillator 6 to form a phase locked loop. when the phase locked loop is locked normally, since the frequency to the phase comparator 5 is equal, the relation of f0+(1/N-1/M)f1 is established to form a synthesis circuit having a frequency mixture ratio of (1/N-1/M) thereby decreasing the minimum step of frequency control.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a digitally controlled frequency synthesizer, and particularly to a digitally controlled frequency synthesizer whose frequency synthesis ratio can be controlled by an external digital signal in a voltage controlled oscillator using a frequency synthesis method. Concerning vessels.

[Conventional technology]

Conventionally, the configuration of a frequency synthesizer in which the frequency synthesis ratio is externally controlled is as shown in the circuit configuration diagram of FIG. 3, in which the input signal f! is input, and the frequency divider 12 is controlled by a control signal with a frequency division ratio of 1/N from the control terminal 18. On the other hand, if the desired output signal f of the output terminal 17 is assumed, then this output signal f.

The frequency divider 13 is controlled by a control signal having a frequency division ratio of 1/M from the control terminal 19. The same frequencies f t /N and fo/M of the output signals of these two frequency dividers 12 and 13 are phase-compared by a phase comparator 14, and are subjected to voltage control via a low-pass filter 15. At the oscillation frequency of oscillator 16. , that is, f.

The phase of M/N f 1 was controlled. Here, the frequency synthesis ratio is M/N. The frequency control step changes depending on the values of M and N, but when M = N + 1, the control step is the minimum.At this time, the value of N changes by ], but the frequency change of the frequency synthesizer is expressed as (]) % Equation % (1) (As shown in Equation 11, the frequency synthesis ratio changes by approximately 1/N2. 5. The minimum value of the controllable frequency control step of the conventional frequency synthesizer is approximately 1/N1. In order to make this control step smaller, it was necessary to increase the value of N.

[Problem to be solved by the invention]

In the conventional digitally controlled frequency synthesizer described above, the minimum value of the controllable frequency control step of the frequency synthesizer is approximately 1.
/N2, so in order to make this control step smaller, it is necessary to increase the value of N, which increases the size of one circuit and slows down the response of the phase locked circuit.
It has the disadvantage that transient fluctuations cannot be ignored.'1-
16 [Means for Solving the Problems] The digitally controlled frequency synthesizer of the present invention is a digitally controlled frequency synthesizer having a voltage controlled oscillator that obtains an output signal of an arbitrary frequency by a frequency synthesis method, in which a signal input from the outside is a control means for outputting two control signals for setting a frequency division ratio of the first and second frequency dividers; a frequency mixer that inputs and frequency-converts the frequency-divided output signal of the frequency converter and the output signal of the voltage controlled oscillator; a low-pass filter that extracts the low-frequency output signal of the frequency mixer; a phase comparator that inputs the output signal of the frequency divider and the divided output signal of the second frequency divider and performs phase comparison; 1-1 inputs the control signal of the phase comparator to the voltage controlled oscillator; to form a phase-locked loop.

〔Example〕

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

First, Figure 8 is a circuit configuration diagram of the first embodiment of the present invention.
Frequency divider 1 and frequency divider 2 convert input signals f1 of input terminals] and 0 into 1/N by control signals of control terminals 18 and 19, respectively.
, 1/M.

The frequency mixer 3 adjusts the frequency fx/of the output signal of the frequency divider 1.
N and the frequency fO of the output signal of the voltage controlled oscillator 6 are frequency-mixed, and a signal having the sum and difference frequency components is output. The low-pass filter 4 is a filter that passes the low frequency side of the output of the frequency mixer 3.

The phase comparator 5 detects the frequency f of the output of the low-pass filter 4.

/N-fo and the phase of the frequency f1/M of the output of the frequency divider 2 are compared, and a frequency control signal of the voltage controlled oscillator 6 is outputted,
Forms a phase-locked loop. Therefore, the input frequency is f
l and the output frequency is fO. When the phase-locked loop is normally synchronized, the frequencies to the phase comparator 5 are equal, so fo + (1/N 1/M)fl
The relationship holds true.

In this way, the frequency mixer and the frequency division ratio N of the two frequency dividers
By controlling the values of and M, it is possible to configure a frequency synthesis circuit having a frequency synthesis ratio of (1/N-i/M). Therefore, when M=N+1-, the combination ratio is 1. /N(N+1
>, and in this case, the minimum step of frequency control is approximately 2
/ N.

Next, a second embodiment of the present invention will be described with reference to the circuit configuration diagram in FIG. In FIG. 2, a frequency divider 1°2, a frequency mixer 3, a low-pass filter 4, a phase comparator 5, a voltage controlled oscillator 6
, input terminal of input signal f1] 0, output signal f. The output terminal] 7 has the same configuration as the first embodiment. In the second embodiment, the control signals for the division ratios N and M of the frequency divider 12 are controlled by a digital-to-digital converter 7 (ROM).

That is, when the desired operating condition information of the frequency synthesizer is inputted by the control signal 7A inputted from the outside, the pre-stored frequency division ratios N and M of this condition are read out, and the frequency divider] , 2 are set. The subsequent operations are the same as in the first embodiment.

〔Effect of the invention〕

As explained above, the present invention controls the values of the frequency division ratios N and M of the frequency mixer and the two frequency divider circuits L (1/N-1,/M
), and by setting the values of the dividing ratios N and M using an external control signal or a pre-stored digital-to-digital converter, the frequency of the conventional example can be changed. While the minimum step of the synthesis ratio was 1/N, this has the effect of significantly reducing the control step.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a first embodiment of the present invention, Fig. 2 is a circuit diagram of a second embodiment of the invention, and Fig. 3 is a circuit diagram of a conventional digitally controlled frequency synthesis circuit. be. 1.2... Frequency divider, 3... Frequency mixer, 4...
Low-pass filter, 5... Phase comparator, 6... Voltage controlled oscillator, 7... Digital-digital converter, 10.
...Input terminal, 17...Output terminal, 18.19...
Control terminal.

Claims (1)

[Claims] A digitally controlled frequency synthesizer having a voltage controlled oscillator that obtains an output signal of an arbitrary frequency by a frequency synthesis method, comprising: a control means for outputting two control signals for setting a frequency division ratio of a signal input from the outside; A frequency is determined by inputting first and second frequency dividers whose frequency division ratios are set by each of two control signals, and the frequency division output signal of the first frequency divider and the output signal of the voltage controlled oscillator. A frequency mixer for conversion, a low-pass filter for taking out a low-frequency output signal of the frequency mixer, and an output signal of the low-pass filter and a frequency-divided output signal of the second frequency divider are input. A digitally controlled frequency synthesizer comprising: a phase comparator that performs phase comparison; and a phase-locked loop is formed by inputting a control signal of the phase comparator to the voltage controlled oscillator.