JPH06216771A - Frequency synthesizer - Google Patents

Abstract

PURPOSE:To shorten the time until locking with a desired frequency can be obtained. CONSTITUTION:A voltage generator 8 which outputs a voltage set in advance is provided. A first analog switch 9 which switches whether or not the output voltage of the voltage generator 8 should be applied to a loop filter 4 provided. A second analog switch 10 which switches whether or not the output of a phase comparator 3 should be outputted to the loop filter 4 is provided. A controller 7 turns on the analog switch 9 and turns off the analog switch 10 before a frequency dividing ratio of a fixed frequency divider 2 to a variable frequency divider 6 is controlled. Thereby. such control that a voltage controlled oscillator 5 oscillates with a frequency near to the desired frequency is performed in advance before the desired frequency is obtained. A feedback loop can be formed by turning off the analog switch 9 and turning on the analog switch 10 at a stage where the frequency dividing ratio of the fixed frequency divider 2 to the variable frequency divider 6 is controlled. Thereby, it is possible to make the feedback loop easy to lock with the desired frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency synthesizer for obtaining a plurality of desired frequencies.

[0002]

2. Description of the Related Art A frequency synthesizer is used to obtain a plurality of desired frequencies in a device for transmitting information using a plurality of channels. As shown in FIG. 3, the frequency synthesizer includes a reference signal oscillator 1 that generates a signal of a reference frequency, a fixed frequency divider 2 that divides the frequency of the reference signal, and an oscillation frequency that is variable according to a control voltage. Flexible voltage-controlled oscillator 5, variable frequency divider 6 for dividing the output of voltage-controlled oscillator 5, fixed frequency divider 2 and variable frequency divider 6
And a phase comparator 3 that compares the phases of the outputs with each other to generate a signal corresponding to the phase difference, and a loop filter 4 that integrates the output of the phase comparator and generates a control voltage corresponding to the phase difference. The control unit 7 controls the frequency division ratio of the fixed frequency divider 2 and the variable frequency divider 6 to obtain a desired frequency.

In the above frequency synthesizer, the control device 7
In accordance with the desired frequency, the fixed frequency divider 2 and the variable frequency divider 6
The frequency division ratio is set, and feedback is applied so as to eliminate the phase difference of the phase comparator 3 in the feedback loop including the phase comparator 3, the loop filter 4, the voltage controlled oscillator 5, and the variable frequency divider 6. Then, a desired frequency can be obtained as the output of the voltage controlled oscillator 5 when the phase difference disappears.

[0004]

By the way, in the conventional frequency synthesizer, when the feedback loop is locked to a specific frequency, it takes time until the desired frequency is obtained because the locking process is performed through the frequency pulling process. There was a problem. The present invention has been made in view of the above points, and an object of the present invention is to provide a frequency synthesizer that can shorten the time until the feedback loop is locked to a specific frequency as much as possible.

[0005]

According to the present invention, in order to achieve the above object, a reference signal oscillator for generating a signal of a reference frequency, a fixed frequency divider for dividing the frequency of the reference signal, and a control are provided. Voltage-controlled oscillator whose oscillation frequency is variable according to voltage, variable frequency divider that divides the output of the voltage-controlled oscillator, and phase of each output of the fixed frequency divider and variable frequency divider , A phase comparator that generates a signal according to the phase difference, a loop filter that integrates the output of the phase comparator and generates a control voltage according to the phase difference, and a fixed frequency divider according to the desired frequency. Device for controlling the frequency division ratio between the voltage divider and the variable frequency divider, a voltage generator for outputting a preset voltage for oscillating the voltage controlled oscillator at a frequency close to a desired frequency, and a voltage generator Mark the output voltage of the device on the loop filter A first analog switch for switching whether to output or not, and a second analog switch for switching whether to output the output of the phase comparator to the loop filter, and a fixed frequency divider to obtain a desired frequency. Before controlling the frequency division ratio with the variable frequency divider, the control device turns on the first analog switch and turns off the second analog switch to make the voltage controlled oscillator have a frequency close to a desired frequency. The first analog switch is turned off and the second analog switch is turned on when the frequency division ratio between the fixed frequency divider and the variable frequency divider is controlled.

Note that for all desired frequencies,
In order to shorten the time until the feedback loop is locked, it is preferable that the control device changes the output voltage of the variable voltage generator according to the desired frequency.

[0007]

The present invention provides a voltage generator for outputting a preset voltage for causing the voltage controlled oscillator to oscillate at a frequency close to a desired frequency as described above, and a loop filter for the output voltage of the voltage generator. And a second analog switch for switching whether to output the output of the phase comparator to the loop filter, and a fixed frequency division for obtaining a desired frequency. The controller turns on the first analog switch and controls the second analog signal before controlling the frequency division ratio between the frequency divider and the variable frequency divider.
Is turned off, the voltage-controlled oscillator is oscillated at a frequency close to the desired frequency, and the frequency division ratio between the fixed frequency divider and the variable frequency divider is controlled, the first analog switch Is turned off and the second analog switch is turned on to oscillate the voltage-controlled oscillator at the time of initial operation when obtaining the desired frequency at a frequency close to the desired frequency, and to detect the phase comparator, the loop filter, A feedback loop composed of a voltage controlled oscillator and a variable frequency divider is easily locked to a desired frequency, and the time until locking is shortened.

Further, the control device changes the output voltage of the variable voltage generator according to a desired frequency,
For all desired frequencies, oscillate the voltage-controlled oscillator at the time of initial operation when obtaining the desired frequency at a frequency close to the desired frequency, making it easy to lock the feedback loop to the desired frequency, and The time to lock uniformly to the desired frequency of is shortened.

[0009]

FIG. 1 shows an embodiment of the frequency synthesizer of the present invention. In the present embodiment, in the conventional frequency synthesizer described with reference to FIG. 3, a voltage generator 8 that outputs a preset voltage and whether to apply the output voltage of the voltage generator 8 to the loop filter 4 are switched. A first analog switch 9 and a second analog switch 10 for switching whether to output the output of the phase comparator 3 to the loop filter 4 are newly provided, and the analog switches 9 and 10 are provided.
The switching control is performed by the control device 7.

First, before controlling the frequency division ratio of the fixed frequency divider 2 and the variable frequency divider 6 to obtain a desired frequency, the control device 7 turns on the analog switch 9 and the analog switch. 10 is turned off, and the voltage controlled oscillator 5 is oscillated at a constant frequency. Here, the output voltage of the voltage generator 8 is set so that the frequency oscillated by the voltage controlled oscillator 5 at this time is close to the desired frequency. For example, the output voltage of the voltage generator 8 may be set so that the voltage controlled oscillator 5 oscillates at the center frequency of the frequency band of the desired frequency.

Then, when the control device 7 controls the frequency division ratio between the fixed frequency divider 2 and the variable frequency divider 6, the analog switch 9 is turned off and the analog switch 10 is turned on.
Phase comparator 3, loop filter 4, voltage controlled oscillator 5
And a feedback loop composed of the variable frequency divider 6 is formed. After that, the phase comparator 3
Feedback is applied so as to eliminate the phase difference of, and the frequency is locked to a desired frequency. In this way, the voltage controlled oscillator 5
Can be oscillated in advance at a frequency close to the desired frequency, and the time until locked to the desired frequency can be shortened. For example, without going through the frequency pulling process in a conventional frequency synthesizer of this type,
Since the process immediately shifts to the lock process, the time required to lock to the desired frequency can be shortened. Also,
The time for charging the capacitor of the loop filter 4 can also be shortened by applying the output voltage of the voltage generator 8 to the loop filter 4 in advance, which contributes to shortening the time until locked to a desired frequency. .

In the above case, a predetermined voltage is applied to the loop filter 4 before controlling the frequency division ratio of the fixed frequency divider 2 and the variable frequency divider 6 in order to obtain a desired frequency. It was something to do. In this case, the frequency at which the voltage controlled oscillator 5 oscillates is not uniformly close to all desired frequencies. In other words, the time required for locking varies depending on the desired frequency.

Therefore, in order to improve this point, a variable voltage generator 8'may be used instead of the voltage generator 8 and the output voltage of the variable voltage generator 8'may be changed according to a desired frequency. . That is, as shown in FIG. 2, the control device 7 is provided with a control line for adjusting the output voltage of the variable voltage generator 8 ', and the voltage controlled oscillator 5 has an oscillation frequency that is easily locked according to a desired frequency. Vary the oscillation frequency of.

With this configuration, it is possible to shorten the time required to lock uniformly at all desired frequencies. However, in this case, the control device 7 needs to know the next desired frequency in advance, for example, by cyclically cycling the desired frequency and switching.

[0015]

As described above, the present invention provides a voltage generator for outputting a preset voltage for oscillating a voltage controlled oscillator at a frequency close to a desired frequency, and an output voltage of the voltage generator. A first analog switch for switching whether to apply to the loop filter and a second analog switch for switching whether to output the output of the phase comparator to the loop filter.
Before controlling the division ratio of the fixed frequency divider and the variable frequency divider to obtain the desired frequency, the analog switch of
The control device turns on the first analog switch and turns off the second analog switch to oscillate the voltage-controlled oscillator at a frequency close to a desired frequency. Since the first analog switch is turned off and the second analog switch is turned on at the stage of controlling the frequency division ratio between and, the voltage controlled oscillator at the initial operation point when obtaining the desired frequency is desired. It is possible to oscillate at a frequency close to the frequency, which makes it easy to lock the feedback loop consisting of the phase comparator, loop filter, voltage-controlled oscillator, and variable frequency divider to the desired frequency, and shorten the time until locking can do.

Further, the control device changes the output voltage of the variable voltage generator according to the desired frequency,
For all desired frequencies, the voltage-controlled oscillator at the time of initial operation when obtaining the desired frequency can be made to oscillate at a frequency close to the desired frequency, and the feedback loop can be easily locked to the desired frequency. It is possible to shorten the time required to uniformly lock to the desired frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of another embodiment.

FIG. 3 is a block diagram showing a circuit configuration of a conventional example.

[Explanation of symbols]

 1 Reference Signal Oscillator 2 Fixed Divider 3 Phase Comparator 4 Loop Filter 5 Voltage Controlled Oscillator 6 Variable Divider 7 Control Device 8 Voltage Generator 8'Variable Voltage Generator 9 First Analog Switch 10 Second Analog switch

Claims (2)

[Claims] 1. A reference signal oscillator that generates a signal of a reference frequency, a fixed frequency divider that divides the frequency of the reference signal, and a voltage-controlled oscillator whose oscillation frequency is variable according to a control voltage. Phase comparison that compares the phase of the variable frequency divider that divides the output of the voltage controlled oscillator with the output of each of the fixed frequency divider and the variable frequency divider, and generates a signal according to the phase difference , A loop filter that integrates the output of the phase comparator to generate a control voltage according to the phase difference, and a control device that controls the frequency division ratio of the fixed frequency divider and the variable frequency divider according to the desired frequency A voltage generator for outputting a preset voltage for oscillating the voltage controlled oscillator at a frequency close to a desired frequency, and switching whether to apply the output voltage of the voltage generator to the loop filter. 1 analog switch and phase A second analog switch for switching whether to output the output of the comparator to the loop filter, and before controlling the frequency division ratio of the fixed frequency divider and the variable frequency divider to obtain a desired frequency. , The control device turns on the first analog switch, turns off the second analog switch, and oscillates the voltage controlled oscillator at a frequency close to a desired frequency. A frequency synthesizer characterized in that the first analog switch is turned off and the second analog switch is turned on at the stage of controlling the frequency division ratio with the device. 2. The frequency synthesizer according to claim 1, wherein the control device changes the output voltage of the variable voltage generator according to a desired frequency.