JPH0974315A - Modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an occupied frequency zone for each channel into a fixed range while keeping the circuit scale small even when any channel is changed by compensating the controlled voltage change amount/frequency transition amount characteristics of a voltage controlled oscillator(VCO) without increasing the number of parts and without inputting any control signal from the outside even when these characteristics are not flat. SOLUTION: On the input side of a VCO 6, a voltage controlled amplifier 5 having controlled voltage/amplification factor characteristics inverse to the controlled voltage change amount/frequency transition amount characteristics of the VCO 6 is provided. While using the voltage controlled amplifier 5, the value of modulation wave is adjusted and inputted to the VCO 6 by an amplification factor to be continuously changed corresponding to the value of control voltage inputted to the VCO 6, and the transmission wave outputted from the VCO 6 is angle-modulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation circuit used in a multi-channel transmitter or the like.

[0002]

2. Description of the Related Art In a transmitter for multi-channel transmission, a modulated wave to be transmitted is placed on a carrier of a designated channel, and a carrier of the channel designated by a modulation circuit is generated in order to transmit the carrier. However, the carrier wave is modulated by a modulated wave to generate a transmission signal.
FIG. 6 is a block diagram showing an example of a transmission unit using a frequency synthesizer type modulation circuit among such modulation circuits. A transmission unit 101 shown in this figure generates a transmission wave by angularly modulating the carrier wave with a modulation wave such as audio data to be transmitted, while generating a carrier wave by a frequency synthesizer method based on an input channel setting signal. A frequency synthesizer type modulation circuit 102, a preamplifier 103 for preamplifying the transmission wave output from the modulation circuit 102, and a preamplified transmission wave output from the preamplifier 103. And a power amplifier 104 that takes in and amplifies the power.

Then, while generating a carrier wave having a frequency corresponding to the value of the input channel setting signal, the carrier wave is modulated by the input modulation wave to generate a transmission wave, and this is pre-amplified and power-converted. It is amplified to form a transmission wave having sufficient amplitude and power, and is transmitted from the antenna 105. As shown in FIG. 7, the modulation circuit 102 includes a reference oscillator (RE) that generates a reference frequency signal (reference frequency signal).
(F · OSC) 106 and a phase of a reference frequency signal output from the reference oscillator 106 and a phase of a signal fed back (feedback signal) are compared, and a phase comparator for generating a control voltage according to the comparison result is compared. (PD) 1
07, a control voltage output from the phase comparator 107, and a low-pass filter circuit (LPF) 108 for low-pass filtering, and the low-pass filter circuit 10.
And a voltage controlled oscillator (VCO) 109 that oscillates at a frequency corresponding to the value of the control voltage output from 8 and the value of the input modulated wave to generate a transmitted wave, and this voltage controlled oscillator 1
The pre-frequency divider (PS) 110 that takes in and divides the transmission wave that is output from the pre-frequency divider 110 and the pre-divider transmission wave that is output from the pre-frequency divider 110 is taken in, and the specified division is performed. A PLL (Phase Locked Loop) circuit including a variable frequency divider 111 that divides a frequency by a frequency ratio (value of a channel setting signal) to generate a feedback signal and feeds it back to the phase comparator 107. Has been done.

While controlling the voltage-controlled oscillator 109 with the input modulated wave in a state in which the frequency division rate of the variable frequency divider 111 is set to the frequency division rate according to the value of the input channel setting signal. The voltage-controlled oscillator 109 is oscillated to generate a transmission wave having a frequency corresponding to the value of the channel setting signal and the value of the modulation wave. In this case, the voltage-controlled oscillator 109 used in the above-described frequency synthesizer type modulation circuit 102 includes a capacitor 112 and a resistor 113 that receive a modulated wave such as audio data and cut a DC component as shown in FIG. These capacitors 112
And a variable capacitance diode 114 having a capacitance according to the modulated wave that has passed through the resistor 113 and the input control voltage,
A delay circuit 115 for delaying a signal input according to the capacitance of the variable capacitance diode 114, and the delay circuit 1
The amplifier 116 is provided with a signal output from the amplifier 15, which is amplified and then fed back to the input side of the delay circuit 115, and a buffer amplifier 117 which receives and amplifies the signal output from the amplifier 116. The delay circuit 115 adjusts the capacitance of the variable capacitance diode 114 based on the modulated wave such as audio data and the control voltage.
By adjusting the delay time of the delay circuit 115,
While oscillating this while adjusting the frequency of the loop type variable oscillating circuit constituted by and the amplifier 116, the buffer amplifier 117 takes out and outputs the signal in the loop type variable oscillating circuit.

By the way, in the voltage controlled oscillator 109 used in the frequency synthesizer type modulation circuit 102, when the value of the control voltage or the like is changed in order to obtain a desired channel frequency, the voltage is controlled. The oscillation frequency changes accordingly. However, at this time, if the value of the control voltage or the like changes, the modulation sensitivity of the variable capacitance diode 114 changes, so that the value of the control voltage or the like changes as shown by the solid line in FIG. On the other hand, the change of the oscillation frequency is not linear, and the shift amount of the frequency changes according to the value of the control voltage. For this reason, even if the magnitude of the modulated wave is the same, the frequency shift amount is different for each channel, and the frequency occupied area (bandwidth) is changed for each channel.

Therefore, as a method for eliminating such a problem, conventionally, as shown in FIG.
A plurality of attenuators (ATT) 120 for attenuating the modulated wave at different attenuation rates, and the attenuators 102 according to the value of the band switching signal output from the CPU circuit (not shown). Switch circuit 12 for selecting any one of the above and taking in the attenuated modulated wave output from the attenuator 102 and inputting it to the voltage controlled oscillator 109.
1 and the control voltage value is switched to change the channel, the CPU circuit or the like determines which band the changed channel belongs to, and switches the value of the band switching signal based on the determination result. Switch circuit 1
A circuit has been proposed in which the frequency shift amount of the transmission wave output from the voltage controlled oscillator 109 is flattened by switching the attenuator 120 selected in 21. As a result, even when the control voltage change amount / frequency deviation amount characteristic of the voltage controlled oscillator 109 is not flat as shown in FIG. 11, it can be compensated for each band and made almost flat.

[0007]

However, in such a method, since the control voltage change amount / frequency shift amount becomes discontinuous at the band switching point, the control voltage change amount / frequency shift amount is changed. When you want to make the characteristics flat,
There is a problem that the number of bands has to be increased and the number of attenuators 120 has to be increased correspondingly. Further, in such a method, since a band switching signal is required when performing an operation test of the circuit, the operation test of the frequency synthesizer type modulation circuit 102 and the voltage controlled oscillator 109 cannot be performed alone. However, there is a problem that the work efficiency is poor as compared with the case where adjustment can be performed for each unit. In view of the above circumstances, the present invention does not increase the number of parts and does not input a control signal from the outside, even when the control voltage change amount / frequency deviation amount characteristic characteristic of the voltage controlled oscillator is not flat.
This can be compensated for and flattened, which allows the frequency shift to be flattened and the frequency occupancy range for each channel to be constant even when the channel is changed while keeping the circuit scale small. It is an object of the present invention to provide a modulation circuit that can be used.

[0008]

In order to achieve the above object, a modulation circuit according to the present invention is provided with a voltage oscillating at an oscillation frequency corresponding to the value of an input control signal and the value of an input modulated wave. In a modulation circuit having a controlled oscillator, a voltage controlled amplifier having a voltage / amplification characteristic opposite to the voltage / frequency deviation characteristic of the voltage controlled oscillator is arranged on the input side of the voltage controlled oscillator, The control voltage input to the voltage control type oscillator is input to the voltage control type amplifier, and while the amplification degree of the voltage control type amplifier is adjusted, the modulated wave is amplified by the voltage control type amplifier and then amplified. It is characterized in that the already-modulated wave is inputted to the voltage controlled oscillator to oscillate.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 is a block diagram showing an embodiment of a modulation circuit according to the present invention. The modulation circuit 1 shown in this figure is fed back with a reference oscillator (REF / OSC) 2 for generating a signal of a reference frequency (reference frequency signal) and the phase of the reference frequency signal output from the reference oscillator 2. A phase comparator (PD) 3 that compares the phase of a signal (feedback signal) and generates a control voltage according to the comparison result, and the control voltage output from the phase comparator 3 are fetched and low-pass filtered. A low-pass filter circuit (LPF) 4 and a voltage-controlled amplifier (V that amplifies the input modulated wave with an amplification factor according to the value of the control voltage output from the low-pass filter circuit 4).
CA) 5 and.

Further, the modulation circuit 1 oscillates and transmits at a frequency according to the value of the modulated wave output from the voltage control type amplifier 5 and the value of the control voltage output from the low pass filter circuit 4. Voltage controlled oscillator (VC)
O) 6, a prescaler (PS) 7 that takes in and divides the transmission wave output from the voltage-controlled oscillator 6, and a prescaler output from the prescaler 7 A variable frequency divider 8 is provided, which takes in a transmission wave, divides it by a designated frequency division ratio (value of a channel setting signal) to generate a feedback signal, and feeds it back to the phase comparator 3. .

In this case, the voltage control type amplifier 5 is composed of a dual gate FET (field effect transistor) or the like in which the modulated wave is input to one gate and the control voltage is input to the other gate. , When the control voltage of the voltage controlled oscillator 6 is changed by adjusting the bias and the like of the drain and the source of the dual gate FET, the control voltage change amount / frequency shift amount characteristic of the voltage controlled oscillator 6 and The amplification degree of the modulated wave is adjusted by the control voltage / amplification degree characteristics that are reversed, and the frequency deviation of the transmission wave output from the voltage controlled oscillator 6 is made flat.

Next, the operation of this embodiment will be described with reference to the block diagram shown in FIG. << Case where Voltage Controlled Oscillator 6 has Positive Characteristic >> First, as the control voltage change amount / frequency deviation amount characteristic of the voltage controlled oscillator 6 becomes higher as the control voltage becomes higher as shown by the solid line in FIG. When the amount becomes large (when it has a positive characteristic), a voltage using a dual gate FET or the like having a control voltage / amplification characteristic in which the amplification degree decreases as the control voltage increases as shown in FIG. A controlled amplifier 5 is used. As a result, in the voltage controlled oscillator 6 alone, the frequency deviation increases as the control voltage increases, but in the voltage controlled amplifier 5 alone, the amplification degree decreases as the control voltage increases, and the voltage control is performed. Since the value of the modulated wave input to the oscillator 6 is lowered,
Regardless of the value of the control voltage, the frequency deviation of the transmitted wave output from the voltage controlled oscillator 6 is flattened as shown by the dotted line in FIG. The frequency deviation of the transmission wave output from the controlled oscillator 6 has a flat relationship.

<< When Voltage Controlled Oscillator 6 has Negative Characteristic >> Further, as the control voltage change amount / frequency deviation amount characteristic of the voltage controlled oscillator 6 becomes higher as the control voltage becomes higher as shown by the solid line in FIG. When the amount of frequency deviation is small (when it has a negative characteristic), the amplification degree decreases as the control voltage increases as shown in FIG. The dual-gate FET is arranged in the
A voltage controlled amplifier 5 with an inverting amplifier input to is used. As a result, in the voltage controlled oscillator 6 alone, the frequency shift decreases as the control voltage increases, but in the voltage controlled amplifier 5 alone, the amplification degree increases as the control voltage increases as shown in FIG. Since the value of the modulated wave input to the voltage controlled oscillator 6 rises, the value of the control voltage is output from the voltage controlled oscillator 6 as shown by the dotted line in FIG. With the amount of frequency deviation of the transmission wave kept constant, the voltage change of the modulation wave and the frequency deviation of the transmission wave output from the voltage controlled oscillator 6 have a flat relationship.

<< Operation of Entire Modulation Circuit 1 >> Next, after the above setting is completed, the start of the modulation operation is instructed while the variable frequency divider 8 is supplied with the channel setting signal designating the transmission channel. Then, the reference oscillator 2 and the voltage-controlled oscillator 6 start oscillating operation, and the reference frequency signal is output from the reference oscillator 2, which is input to the phase comparator 3 and also from the voltage-controlled oscillator 6. The transmitted wave is output, and after being divided by the prescaler 7, the variable divider 8
Then, the frequency is again divided, and the signal obtained by this dividing operation is input to the phase comparator 3 as a feedback signal. Then, the phase comparator 3 causes the reference oscillator 2
Of the reference frequency signal output from the variable frequency divider 8
Is compared with the phase of a feedback signal output from the control signal to generate a control voltage required to make the phase difference zero, and the low-pass filter circuit 4 low-pass filters the control voltage to generate the control voltage. Amplifier 5,
It is input to the voltage controlled oscillator 6.

As a result, the frequency of the transmission wave output from the voltage controlled oscillator 6 is the frequency of the reference frequency signal output from the reference oscillator 2 multiplied by the reciprocal of the division ratio of the prescaler 7. Further, it is set to a value obtained by multiplying the frequency division ratio of the variable frequency divider 8 by the reciprocal. In this state, if a modulated wave such as audio data is input, the modulated wave is amplified by the voltage control type amplifier 5 at an amplification factor according to the value of the control voltage, and this is input to the voltage control type oscillator 6. The transmitted wave output from the voltage controlled oscillator 6 is angle-modulated.

As described above, in this embodiment, the input side of the voltage controlled oscillator 6 is controlled by the control voltage / the amount of frequency deviation which is opposite to the control voltage change amount / frequency shift amount characteristic of the voltage controlled oscillator 6.
A voltage-controlled amplifier 5 having an amplification characteristic is provided, and the voltage-controlled amplifier 5 generates a modulated wave with an amplification factor that continuously changes according to the value of the control voltage input to the voltage-controlled oscillator 6. The value is adjusted and input to the voltage controlled oscillator 6, and the transmission wave output from the voltage controlled oscillator 6 is angle-modulated. Therefore, the control voltage change amount / frequency of the voltage controlled oscillator 6 is changed. Even when the deviation amount characteristic is not flat, it can be compensated and made flat without increasing the number of parts and without inputting a control signal from the outside. Even when is changed, the frequency deviation can be flattened and the frequency occupancy area for each channel can be made constant. Further, by omitting the processing such as band switching conventionally performed by the CPU circuit and the like, the CPU
It is possible to reduce the burden on the circuit and software, and also to eliminate extra wiring such as band switching lines. Further, in the above-described embodiment, the voltage controlled oscillator 6 and the voltage controlled amplifier 5 are described as independent components, but the voltage controlled amplifier 5 is incorporated into the voltage controlled oscillator 6 and the It may be used as one component.

[0017]

As described above, according to the present invention, even when the control voltage change amount / frequency deviation amount characteristic of the voltage controlled oscillator is not flat, the number of parts is not increased and a control signal is externally supplied. This can be compensated for and flattened without inputting the signal, which keeps the circuit size small and flattens the frequency deviation even when the channel is changed, thereby keeping the frequency occupation area of each channel. Can be constant.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a modulation circuit according to the present invention.

FIG. 2 is a graph showing an example of control voltage / oscillation frequency (frequency shift) when the voltage controlled oscillator shown in FIG. 1 has a positive characteristic.

FIG. 3 is a graph showing an example of control voltage / amplification degree characteristics of the voltage controlled amplifier shown in FIG.

FIG. 4 is a graph showing an example of control voltage / oscillation frequency (frequency shift) when the voltage controlled oscillator shown in FIG. 1 has a negative characteristic.

5 is a graph showing another example of the control voltage / amplification characteristic of the voltage controlled amplifier shown in FIG.

FIG. 6 is a block diagram showing an example of a transmission unit of a general transmitter.

7 is a block diagram showing a detailed configuration example of the modulation circuit shown in FIG.

8 is a block diagram showing a detailed configuration example of the voltage controlled oscillator shown in FIG.

9 is a graph showing an example of control voltage / oscillation frequency (frequency shift) of the voltage controlled oscillator shown in FIG.

FIG. 10 is a block diagram illustrating a conventional circuit for compensating an example of control voltage / oscillation frequency (frequency deviation) of a voltage controlled oscillator.

11 is a graph illustrating the compensation characteristic of the circuit shown in FIG.

[Explanation of Codes] 1 Modulation Circuit 2 Reference Oscillator 3 Phase Comparator 4 Low-pass Filter Circuit 5 Voltage Controlled Amplifier 6 Voltage Controlled Oscillator 7 Prescaler 8 Variable Divider

Claims (1)

[Claims] 1. A modulation circuit having a voltage-controlled oscillator that oscillates at an oscillation frequency according to the value of an input control signal and the value of an input modulated wave, wherein an input side of the voltage-controlled oscillator comprises: A voltage-controlled amplifier having a voltage / amplitude characteristic opposite to the voltage / frequency shift characteristic of the voltage-controlled oscillator is arranged, and the control voltage input to the voltage-controlled oscillator is input to the voltage-controlled amplifier. Then, while the amplification degree of the voltage controlled amplifier is adjusted, the modulated wave is amplified by the voltage controlled amplifier, and the amplified modulated wave is input to the voltage controlled oscillator to oscillate. Modulation circuit to do.