JPH11355139A - Frequency synthesizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the power level of an output signal from being fluctuated by a frequency because the gain of an amplifier is provided with a frequency characteristic. SOLUTION: A frequency synthesizer is provided with a voltage control oscillator 1 outputting a frequency signal corresponding to a control voltage signal, a gain control amplifier 6 outputting an output signal obtained by amplifying the frequency signal through the use of gain corresponding to a gain control signal, a variable frequency divider 2 outputting a frequency dividing signal obtained by frequency-dividing the frequency signal by a frequency dividing ratio corresponding to an output frequency control signal, a phase comparator 3 outputting a pulse signal corresponding to phase difference between the frequency dividing signal and a reference frequency signal, a loop filter 4 converting the pulse signal and outputting it as a control voltage signal and a gain control signal generating circuit 9 consisting of a memory 7 outputting a digital signal corresponding to the output frequency control signal and of a digital/analog converter 8 outputting an analog signal corresponding to the digital signal as the gain control signal. By the configuration, the power level of the output signal is not fluctuated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency synthesizer used for a wireless communication device such as a portable telephone, and more particularly to a frequency synthesizer in which the fluctuation of the power level of an output signal is improved.

[0002]

2. Description of the Related Art A frequency synthesizer used in a radio communication device such as a cellular phone is used to generate a signal of a desired arbitrary frequency, and conventionally, the frequency synthesizer is used in accordance with a voltage of a control voltage signal inputted. VCO (Voltage Controlled Oscillato) that can control the frequency of the output frequency signal
r: a voltage controlled oscillator), a variable frequency divider to which a part of a frequency signal from the VCO is input, and to output a frequency-divided signal obtained by dividing the signal by a predetermined frequency-dividing ratio, and a frequency-divided signal and an external circuit (Phase Locked Loop) circuit comprising a phase comparator for comparing a phase with a reference frequency signal input from the phase comparator and outputting a pulse signal corresponding to the phase difference, and the PLL
The pulse signal from the phase comparator of the circuit is input and the VCO
And a loop filter that outputs a control voltage signal for controlling the voltage.

[0003] Thus, a frequency signal of a desired frequency is synthesized according to the frequency of a reference frequency signal input from an external circuit to a frequency synthesizer, and output as an output signal from the VCO.

In order to secure a power level required by an external circuit receiving the output signal from the frequency synthesizer, an amplifier is usually connected to the VCO which is an output unit to the outside of the frequency synthesizer. The power level of the signal is amplified.

[0005]

However, in the conventional frequency synthesizer as described above, the gain of the amplifier for amplifying the frequency signal output from the VCO has a frequency characteristic, and the frequency of the input signal is low. Since the amplification degree decreases as the frequency increases, the power level of the output signal from the frequency synthesizer fluctuates depending on the frequency.

For this reason, if an external circuit receiving the output is designed in accordance with the power level of the output signal of the frequency synthesizer when the frequency is low, the power level becomes insufficient when the frequency of the output signal increases, resulting in a design failure. There was a problem that it was not possible to obtain the same performance.

When an external circuit receiving the output is designed in accordance with the power level when the frequency of the output signal of the frequency synthesizer is high, when the frequency of the output signal becomes low, the external circuit is There is also a problem that the input of an excessive power level results in distortion of the input signal and generation of unnecessary waves.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to eliminate fluctuations in power level due to frequency of an output signal of a frequency synthesizer and to provide a stable output of a desired power level. An object of the present invention is to provide a frequency synthesizer capable of obtaining a signal.

[0009]

According to the present invention, there is provided a frequency synthesizer, comprising: a voltage controlled oscillator to which a control voltage signal is input and which outputs a frequency signal whose frequency is controlled according to the voltage; Is input, a gain control amplifier that outputs an output signal obtained by amplifying a frequency signal with a gain according to the gain control signal, and a part of the frequency signal and an output frequency control signal are input, and the A variable frequency divider that outputs a frequency-divided signal obtained by dividing a frequency signal by a frequency division ratio; and a phase comparison that receives the frequency-divided signal and a reference frequency signal and outputs a pulse signal corresponding to a phase difference between the two signals. And a loop filter that converts the pulse signal into a DC voltage signal and outputs the DC voltage signal as the control voltage signal; And a gain control signal generating circuit comprising a digital / analog converter for outputting an analog signal having a voltage corresponding to the digital signal as the gain control signal. An object of the present invention is to solve the above problem by making it possible to change the gain of the amplifier, that is, the degree of amplification according to the frequency of the output signal.

[0010]

According to the frequency synthesizer of the present invention, a memory for outputting a digital signal corresponding to a part of an output frequency control signal inputted from an external circuit to a variable frequency divider of a PLL circuit, and a digital synthesizer for the memory are provided. A gain control signal generating circuit comprising a digital / analog converter for outputting an analog signal having a voltage corresponding to the signal as a gain control signal to a gain control amplifier, and amplifying the gain control signal to a frequency signal from a voltage controlled oscillator Since the gain control is performed by inputting to the gain control amplifier, the amplification degree can be changed according to the frequency of the output signal of the frequency synthesizer set by the output frequency control signal, and the frequency of the output signal can be changed. Changes in the power level can be eliminated, and a stable output signal of the desired power level can be obtained. The ones that can Rukoto.

That is, according to the frequency synthesizer of the present invention, in the case of a frequency synthesizer having a conventional amplifier, the amplification decreases as the frequency of the output signal increases, and the power level of the output signal varies with the output frequency. On the other hand, when the output frequency increases in response to the output frequency control signal, the gain of the gain control amplifier, that is, the amplification degree for the output signal can be increased in accordance with the output frequency control signal. The power level of the output signal of the frequency synthesizer can be kept constant regardless of the frequency. As a result, even when the output frequency of the frequency synthesizer is high, the power level of the output signal can be prevented from lowering, and the power level required from an external circuit receiving the output signal can be satisfied regardless of the frequency. In addition, the input of an excessive power level from the frequency synthesizer to the external circuit, the shortage of the input power level, and the like are eliminated, and the performance required for the entire wireless communication apparatus can be stably satisfied.

Next, a frequency synthesizer of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a frequency synthesizer according to the present invention. Reference numeral 1 denotes a voltage controlled oscillator (VC) that receives a control voltage signal and outputs a frequency signal whose frequency is controlled in accordance with the voltage.
O), 2 receives a part of the frequency signal for dividing the output of the voltage controlled oscillator 1 and the output frequency control signal from the control unit 10 which is an external circuit, and has a dividing ratio according to the output frequency control signal. The variable frequency divider 3 outputs a frequency-divided signal obtained by dividing the frequency signal, and the frequency-divided signal 3 from the variable frequency divider 2 and the reference frequency signal fr from the external circuit are input to the variable frequency divider 3. The phase comparator 4 outputs a pulse signal from the phase comparator 3 and converts the pulse signal from the phase comparator 3 into a DC voltage signal and outputs the DC voltage signal as a control voltage signal to the voltage controlled oscillator 1. A PLL circuit 5 is configured by the frequency divider 2 and the phase comparator 3.

Reference numeral 6 denotes a gain control amplifier to which a frequency signal and a gain control signal from the voltage controlled oscillator 1 are input, and which outputs an output signal obtained by amplifying the frequency signal with a gain corresponding to the gain control signal. Reference numeral 7 denotes a memory to which a part of the output frequency control signal from the control unit 10 is input and which outputs a digital signal corresponding to the input, and 8 denotes an analog signal of a voltage corresponding to the digital signal to the gain control amplifier 6 as a gain control signal. A digital / analog converter (D / A) for output,
The memory 7 and the digital / analog converter 8 constitute a gain control signal generation circuit 9.

The memory 7 stores a conversion table between an output frequency control signal and a digital signal to be sent to the digital / analog converter 8, and the digital / analog converter 8 to which the digital signal is input is stored in the memory 7. Is output as the gain control signal to the gain control amplifier 6 to control the gain of the gain control amplifier 6 according to the set frequency.

Reference numeral 10 denotes a control unit as an external circuit for sending an output frequency setting signal for setting the frequency of the output signal of the frequency synthesizer to the PLL circuit 5, and an output frequency setting signal from the control unit 10. Is also sent to the gain control signal generation circuit 9 at the same time.

Next, an operation flow of the frequency synthesizer of the present invention will be described.

First, the frequency signal oscillated according to the control voltage signal in the voltage controlled oscillator 1 and output is partially converted into an output frequency control signal transmitted from the control unit 10 to the variable frequency divider 2 of the PLL circuit 5. The frequency is divided by the variable frequency divider 2 whose division ratio is set accordingly, and the output of the frequency-divided signal is compared with the reference frequency signal fr input from the external circuit by the phase comparator 3. The phase comparator 3 outputs a pulse signal corresponding to the phase difference between the two input signals, and this pulse signal is converted into a DC voltage signal by the loop filter 4 and becomes a control voltage signal for the voltage controlled oscillator 1,
It is input to the voltage controlled oscillator 1. As a result, the oscillation frequency of the voltage controlled oscillator 1 is controlled, and the frequency of the output frequency signal matches the frequency to be set by the output frequency setting signal from the control unit 10.

The frequency signal output from the voltage controlled oscillator 1 is amplified by the gain control amplifier 6 to a desired power level with a desired gain, and output as an output signal from the frequency synthesizer. At this time, P
Part of the output frequency setting signal sent to the variable frequency divider 2 of the LL circuit 5 is also sent to the memory 7 of the gain control signal generating circuit 9. The memory 7 outputs a digital signal corresponding to the output frequency setting signal according to a conversion table stored in advance, and the digital signal is sent to the digital / analog converter 8. And a digital / analog converter 8
Outputs a predetermined analog signal corresponding to the input digital signal, and the analog signal is input to the gain control amplifier 6 as a gain control signal, whereby the gain control amplifier 6 according to the frequency of the output signal of the frequency synthesizer is output. It is possible to obtain a gain.

As described above, in the amplifier of the conventional frequency synthesizer, the gain, that is, the amplification degree tends to decrease as the frequency of the frequency signal input from the voltage controlled oscillator increases. Therefore, in the frequency synthesizer of the present invention, the gain control signal is controlled so that the gain in the gain control amplifier 6 increases when the frequency of the frequency signal is high, so as to compensate for the decrease in gain due to the increase in frequency. Thus, an output signal having a constant power level can be obtained regardless of the frequency.

In addition, since it is not necessary to set the output power higher in anticipation of a decrease in the gain of the amplifier accompanying an increase in the frequency, it is possible to prevent unnecessary waves from being generated in the output signal.

Further, according to the frequency synthesizer of the present invention, not only the power level of the output signal is not merely kept constant but also the power level can be set individually according to the frequency of the output signal. Even when the required input power level differs depending on the frequency band used, such as a frequency multiplier, in an external circuit receiving the output signal, the setting in the gain control signal generating circuit 9 is easily adjusted. be able to.

It should be noted that the above is only an example of the embodiment of the present invention, and the present invention is not limited to this. Various changes and improvements may be made without departing from the gist of the present invention. No problem.

For example, in FIG.
And the variable frequency divider 2, the phase comparator 3, the loop filter 4, the gain control amplifier 6, the memory 7, and the digital / analog converter 8 have been described as individual circuit elements. Needless to say, it may be constituted by

[0025]

According to the frequency synthesizer of the present invention,
An amplifier that amplifies a frequency signal that is normally inserted from a voltage controlled oscillator to an output unit to the outside can be gain controlled,
A gain control signal generation circuit is used to control this gain, and the PLL
By using the output frequency control signal input to the circuit to control the gain, that is, the amplification degree according to the frequency of the output signal, the power level of the output signal does not fluctuate depending on the frequency. Thus, a desired constant output power level could be maintained.

As a result, it is possible to prevent the performance of the external circuit receiving the output signal of the frequency synthesizer from deteriorating due to insufficient power level, and prevent input of an excessive power level from causing signal distortion and unnecessary waves. ,
The output signal of the frequency synthesizer can be provided with a frequency synthesizer capable of obtaining a stable output signal of a desired power level without fluctuation of the power level due to the frequency.

Further, according to the frequency synthesizer of the present invention, the power level of the output signal is not only kept constant even if the frequency changes, but the power level according to the frequency of the output signal can be set individually. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an example of a frequency synthesizer according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Voltage controlled oscillator (VCO) 2 ... Variable frequency divider 3 ... Phase comparator 4 ... Loop filter 6 ... Gain control amplifier 7 ... Memory 8 ... Digital / Analog Converter (D / A) 9 ... Gain control signal generation circuit

Claims (1)

[Claims] A voltage-controlled oscillator that receives a control voltage signal and outputs a frequency signal whose frequency is controlled in accordance with the voltage; a gain that receives the frequency signal and a gain control signal; A gain control amplifier that outputs an output signal obtained by amplifying the frequency signal, and a part obtained by inputting a part of the frequency signal and an output frequency control signal and dividing the frequency signal by a division ratio according to the output frequency control signal. A variable frequency divider that outputs a frequency-divided signal, a phase comparator that receives the frequency-divided signal and a reference frequency signal, and outputs a pulse signal according to a phase difference between the two signals, and converts the pulse signal into a DC voltage signal. A loop filter for converting and outputting the control voltage signal, a memory for receiving a part of the output frequency control signal and outputting a digital signal corresponding thereto, Frequency synthesizer characterized by comprising a a gain control signal generating circuit for an analog signal comprises a digital / analog converter for outputting as the gain control signal voltage.