JP3117802B2 - Modulator temperature compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature compensation circuit for a modulator, and more particularly to an RF modulator for modulating a video signal and an audio signal into a television signal in the UHF band.

[0002]

2. Description of the Related Art FIG. 5 shows a UHF band (300 MHz to 7 MHz).
Conventional RF (Radio Frequenc) used for 00MHz
y) The configuration of the modulator is shown, and the illustrated clamp circuit 1, white clip circuit 2, and FM modulation circuit 3
Are formed in a modulator IC4 configured as an IC (integrated circuit) chip. Therefore, the video signal (video signal) input from the terminal T1 is subjected to white clip processing after being clamped. In addition, the FM
A pre-emphasis circuit 5 comprising a capacitor C1 and a resistor R1 is provided at a stage preceding the modulation circuit 3, and the audio signal input from the terminal T2 is
Thus, the frequency is modulated with the SN ratio improved.

[0003] At the subsequent stage of the modulator IC4, RF
A mixer (diode mixer) 6 and an oscillation circuit (OSC) 7 using discrete transistors are provided.
The RF mixer 6 mixes and modulates the video signal and the audio signal into a carrier wave in the UHF band, and outputs the modulated television (RF) signal from a terminal T3.

[0006] FIG. 6 shows a detailed circuit configuration in the oscillation circuit 7.
1, a tank circuit (tuning circuit) composed of a capacitor C2, a variable condenser 8, a transistor Q1 for amplifying at the time of oscillation, and the like. According to the oscillation circuit 7,
The oscillation frequency is determined by the tank circuit, and the oscillation frequency is converted by the variable setting of the variable condenser 8.

[0005]

However, in the above-described RF modulator, since the variable condenser 8 which mechanically changes the capacitance value in the oscillation circuit 7 is used as described above, the oscillation frequency fluctuates due to vibration and shock. Occurs,
There is also a problem that the temperature characteristics and the moisture resistance are poor. In addition, when frequency conversion is performed by remote control, a mechanical adjusting means is required, which increases the manufacturing cost.

Incidentally, as a method of configuring the oscillation circuit 7 without using the variable capacitor 8, a variable capacitance diode (varactor diode) may be used instead of the variable capacitor 8. However, in this case, the variable capacitance diode has a temperature characteristic in its capacitance, and the problem remains that the oscillation frequency varies with temperature.

Therefore, a temperature compensation circuit which compensates for the temperature characteristic of the variable capacitance diode and enables oscillation at a stable frequency is proposed. In addition, in this case, an RF modulator capable of performing a stable oscillation operation in a wide frequency range is required. That is, even if a temperature characteristic is given to one voltage power supply for converting the capacitance of the varactor diode and the temperature characteristic of the varactor diode is canceled, a predetermined voltage (control voltage) corresponding to a wide frequency range is always maintained. It is difficult to have a temperature characteristic.

The present invention has been made to solve the above problems, and an object of the present invention is to configure an oscillation circuit using a variable capacitance diode, which is affected by the temperature characteristics of the variable capacitance diode. It is an object of the present invention to provide a temperature compensation circuit for a modulator that can stably perform an oscillation operation in a wide frequency range without performing the operation.

[0009]

According to a first aspect of the present invention, there is provided a temperature compensation circuit for a modulator, comprising: a variable capacitance diode for setting an oscillation frequency of the modulator; In the constant voltage circuit for supplying the regulator, there are provided a regulator and temperature-sensitive resistance elements arranged on each of two output sides of the regulator,
A temperature coefficient is given to the two output voltages from the regulator so as to compensate for the temperature coefficient of the variable capacitance diode, and a control voltage formed based on a difference voltage between the two output voltages of the regulator is obtained. It is characterized in that it is supplied to a variable capacitance diode.

A second aspect of the present invention provides a clamp circuit for processing a video signal, a white clip circuit, an FM modulation circuit for processing an audio signal, a voltage-controlled oscillator forming an oscillation circuit, and modulating the video signal and the audio signal. Wherein the mixer according to the first aspect is applied to a modulator in which a dedicated constant voltage circuit is connected to the voltage-controlled oscillator.

[0011]

According to the configuration of the first aspect, the oscillation frequency of the modulator is set and converted by the variable capacitance diode, but the capacitance of the variable capacitance diode changes according to the applied voltage (bias voltage). Will do. In the present invention, a difference voltage between two voltages formed based on the output of the regulator is provided as a voltage to be supplied to the variable capacitance diode, and the two voltage sources that form the difference voltage are provided with the above-described voltage source. A predetermined temperature coefficient for canceling the temperature characteristic of the variable capacitance diode is given by the temperature-sensitive resistance element.

Accordingly, temperature compensation can be performed by the temperature coefficient given to the two voltages, and a constant oscillation frequency (carrier) is formed in the modulator even when there is a temperature change. In this case, since the temperature coefficient is given to both of the two voltages formed based on the regulator output, the temperature coefficient given to the difference voltage can be set to a desired value in a wide voltage range. The temperature coefficient of the variable capacitance diode can be effectively canceled.

According to a second aspect of the present invention, R
Since the F modulator is further miniaturized as compared with the conventional one, and the voltage controlled oscillator is provided with a dedicated constant voltage circuit, it is possible to satisfactorily avoid interference with RF signals from other power supply lines.

[0014]

FIG. 1 shows a configuration of a temperature compensation circuit of a modulator according to an embodiment, and FIG. 2 shows a circuit block in a module IC. First, in FIG.
In a modulator IC 10 configured as an IC chip, an FM modulation circuit for inputting a video signal through a clamp circuit 11, a white clip circuit 12, and an audio signal via a pre-emphasis circuit (consisting of a capacitor C1 and a resistor R1) 13. 14. Low-pass filter (LPF) 1
5 is provided, and a constant voltage circuit 16 for supplying a constant voltage to each of these circuits is provided. Further, in the embodiment, an RF mixer 17 for inputting the outputs of the white clip circuit 12 and the LPF 15, an RF voltage controlled oscillator (VCO) 18 constituting a carrier wave oscillation circuit, and a constant voltage circuit 19 are integrated into an IC, and the modulator IC 10 Formed into.

Therefore, in the embodiment, the size of the RF modulator can be further reduced as compared with the conventional one (FIG. 5). Moreover, as described above, the RFVCO 18 is provided with a dedicated constant voltage circuit 19 so as to separate it from other circuits, thereby avoiding interference from RF power signals from other power supply lines and reducing variations in electrical characteristics. It is designed to suppress.

The FM modulation circuit 14 has an audio FM tank circuit 20 comprising a capacitor C3 and a coil L2.
The RFVCO 18 is further provided with a coil L3, a capacitor C4, and a variable capacitance diode (varactor diode) 22 constituting an oscillation circuit. A constant voltage circuit 23 is connected to the varactor diode 22. The RF signal is output from a terminal T3 connected to the RF mixer 17.

In FIG. 1, a coil L3, a capacitor C4, and a varactor diode 22 constituting an oscillation circuit are different from the connection of FIG.
2 can be connected in series with the coil L3. And
In the constant voltage circuit 23, a shunt regulator 25, temperature-sensitive resistance elements (thermistors and the like) R1, R4, resistors R2, R3 having no temperature coefficient, and a variable resistor R5 are connected and arranged as shown in the figure. That is, the shunt regulator 25
Is supplied with a voltage power supply Vcc. The resistors R1 and R2 are connected so that the voltages output from both the output terminal Vo and the reference voltage terminal Vr are divided by resistors.
, R3, R4, etc., and in order to give the output voltage on the output terminal Vo a temperature coefficient, the resistor R1 is made a temperature-sensitive resistance element, and the reference voltage on the reference voltage terminal Vr is given a temperature coefficient. Therefore, the resistor R4 is a temperature-sensitive resistor.

Then, one end (upper end) of the variable resistor R5
, A voltage V01 is applied from the output terminal Vo side of the shunt regulator 25, and a voltage V02 is applied to the other end (lower end) from the reference voltage terminal Vr side. This voltage V01 and the voltage are applied to the variable resistor R5. A voltage difference of V02 is provided. This state is the same as the state shown in FIG. 3. The variable resistor R5 is sandwiched between the power supply of the voltage V01 and the power supply of the voltage V02, and the voltage VB obtained by dividing the voltage difference between V01 and V02 by the varactor diode 22 is applied. Is supplied as a control voltage for determining the oscillation frequency. Therefore, in the present invention, the temperature compensation is applied to the voltage source for forming the difference voltage of V01-V02.

The voltage V01 and the voltage V02 are given a temperature coefficient represented by the following equation.

## EQU1 ## δV01 / δT = (1 / R2) · Vref · (δR1 / δT) Vref: Reference voltage of shunt regulator

## EQU2 ## δV02 / δT = [R3 / (R3 + R4) ² ] · Vref · (δR4 / δT)

Therefore, δV01 / δT, δV02 in the above equation
The value of / δT is calculated such that the output oscillation frequency is not affected by the temperature, that is, the temperature coefficient of the varactor diode 22 is 1. Then, back calculation is performed from this value to obtain δR1 / δ in the above formulas 1 and 2.
Since T and δR4 / δT are obtained, the temperature-sensitive resistance element R1 should have a temperature coefficient of δR1 / δT, and the temperature-sensitive resistance element R4 should have a temperature coefficient of δR4 / δT. . In the embodiment, for example, the temperature-sensitive resistance element R1 is 1000 ppm / ° C.
4 is used whose resistance changes at 3000 ppm / ° C.

FIG. 4 shows the temperature characteristics of the oscillation frequency in the RF modulator of the embodiment. As shown by a characteristic curve 100 in the case where the temperature compensation is not performed in the conventional device, the temperature characteristics of the varactor diode 22 are shown. As a result, the oscillation frequency decreases linearly. On the other hand, in the embodiment, as shown by the characteristic curve 200, the variable resistor R5
By performing temperature compensation on the difference voltage given to
A constant oscillation frequency can be obtained even if there is a change in temperature. In the example, as illustrated, from -25 ° C to 75 ° C.
± 200 ° C for ambient temperature changes that change in the range of
It can be suppressed to a frequency fluctuation of kHz.

According to the configuration of this embodiment, when the capacitance of the varactor diode 22 is changed by the control voltage divided by the variable resistor R5, the oscillation frequency is switched according to the change in the capacitance of the varactor diode 22. Will be. The oscillation frequency signal is represented by R
The signal is supplied to the RF mixer 17 via the FVCO 18 and is used as a carrier for mixing a video signal and an audio signal.

In the present invention, as shown in FIG. 3, both voltage sources (V
01, V02), the temperature characteristics of the varactor diode 22 can be effectively canceled in a wide range of the voltage applied to the varactor diode 22, and an extremely stable oscillation frequency can be obtained in a wide range. be able to. In the example, the frequency range of the carrier was secured in the UHF band at ± 36 MHz, that is, ± 6 channels, and a good oscillation frequency could be obtained in this frequency range.

Further, in the embodiment, the use of the shunt regulator 25 as a regulator can improve the stability against power supply voltage fluctuations.
There is an advantage that a low voltage operation from 8 V is possible.

Further, the present invention can be applied to other application fields using the varactor diode 22, such as a tuner. As an example, the present invention may be combined with a tuner block of a synthesizer type. In this case, instead of supplying the voltage supplied from the variable resistor R5, the voltage from the tuner block is supplied to the varactor diode 22. , The oscillation frequency can be switched by the tuner block.

Further, in the present invention, since the channel frequency is switched by applying a control voltage to the varactor diode 22, there is an advantage that the channel can be easily switched using a remote controller.

[0027]

As described above, according to the first aspect of the present invention, the oscillation frequency of the modulator is converted by the variable capacitance diode, and the constant voltage circuit is constituted by combining the regulator and the temperature-sensitive resistance element. A predetermined temperature coefficient is given to the two output voltages from the regulator by a temperature-sensitive resistance element so as to compensate for the temperature coefficient of the variable capacitance diode, and a difference voltage between the two output voltages of the regulator is provided. Control voltage is supplied to the variable-capacitance diode, eliminating the need for using a variable capacitor as a mechanical frequency adjustment means, eliminating fluctuations in oscillation frequency due to vibration and shock, and reducing costs. Modulators can be made. Moreover, it is possible to obtain a highly stable oscillation frequency in a wide range of the UHF band in the modulator without being affected by the temperature characteristics of the variable capacitance diode.

According to the second aspect of the present invention, the voltage controlled oscillator constituting the oscillation circuit and the mixer for modulating the video signal and the audio signal are mounted on the same chip as an integrated circuit. There is an advantage that the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a temperature compensation circuit of a modulator according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram illustrating an overall configuration of a modulator according to the embodiment.

FIG. 3 is an explanatory diagram illustrating a simplified configuration of a constant voltage circuit connected to the oscillation circuit of the embodiment.

FIG. 4 is a graph showing a change in an oscillation frequency with respect to a temperature change in the example.

FIG. 5 is a circuit block diagram showing a configuration of a conventional modulator.

FIG. 6 is a circuit diagram showing a detailed configuration in the oscillation circuit of FIG. 5;

[Explanation of symbols]

4,10 ... modulator IC, 3,14 ... FM modulation circuit, 6,17 ... RF mixer, 7 ... oscillation circuit (OSC), 22 ... varactor diode (variable capacitance diode), 16, 19, 23 ... constant voltage circuit, 25: shunt regulator, R1, R4: temperature-sensitive resistance element, R5: variable resistance.

Continuation of front page (56) References JP-A-53-56949 (JP, A) JP-A-58-175306 (JP, A) JP-A-58-172225 (JP, U) JP-A-2-36267 (JP) , U) J. 50-21361 (JP, Y1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03B 5/00-5/42 H03J 3/00-3/32 H04N 5/44

Claims (2)

(57) [Claims] A constant voltage circuit for providing a stable voltage is provided with a variable capacitance diode for setting an oscillation frequency of a modulator, and a regulator and two sensors arranged on each of two output sides of the regulator are provided. A temperature resistance element is provided, and a temperature coefficient is given to two output voltages from the regulator so as to compensate for a temperature coefficient of the variable capacitance diode, and based on a difference voltage between the two output voltages of the regulator. A temperature compensation circuit for a modulator configured to supply the formed control voltage to the variable capacitance diode. 2. An integrated circuit comprising a clamp circuit for processing a video signal, a white clip circuit, an FM modulation circuit for processing an audio signal, a voltage controlled oscillator forming an oscillation circuit, and a mixer for modulating the video signal and the audio signal. 2. The temperature compensation circuit for a modulator according to claim 1, wherein the modulator is mounted on the same chip and is applied to a modulator in which a dedicated constant voltage circuit is connected to the voltage controlled oscillator.