JP2737631B2 - Non-linearity compensation circuit for TV transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linearity compensating circuit for a TV transmitter, and more particularly to a compensating circuit for correcting a black-side amplitude characteristic.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, a video signal output from a TV transmitter has a characteristic that the output voltage level is saturated as the input voltage level increases. Due to this characteristic, as shown in FIG. 6, an unmodulated video signal becomes blacker as the level increases, and therefore, when amplifying with a final stage video amplifier, the black side must be compensated. Therefore, in general, the black-side amplitude compensation circuit is arranged before the last-stage video amplifier and compensates to make the input / output voltage characteristics as a whole linear.

FIG. 7 shows an example of a conventional black-side amplitude compensation circuit. This amplitude compensation circuit includes an N-stage black-side amplitude compensation circuit, a distributor and a combiner. In the amplitude compensation circuit, the amplification degrees of the black-side amplitude compensation circuits Z21 to Z2N are set to different values by setting the emitter resistors R251 to R25N of the transistors TR221 to TR22N to different values. Also, the slope of the output signal is changed by changing the variable resistors VR211 to VR21N connected to the bases of the transistors TR211 to TR21N, respectively. As described above, the conventional black-side amplitude compensation circuit is a circuit in which the individual black-side amplitude compensation circuits Z21 to Z2N are arranged in multiple stages, so that a sufficient compensation amount can be obtained and the compensation amount can be finely adjusted.

[0004] Diodes are generally used in various temperature compensating circuits by using the stability of the forward operating level versus temperature characteristics. In order to obtain a predetermined voltage value or resistance value, a multi-stage parallel connection or series connection method is used. Regarding these technologies, for example, Japanese Patent Publication No. 3-248
No. 15, Japanese Unexamined Patent Publication No. 2-44814, Japanese Unexamined Utility Model Publication No. 2-
No. 8216 and Japanese Utility Model Application Laid-Open No. Sho 62-15220.

[0005]

However, in the final stage video amplifier of the TV transmitter, the non-linearity of luminance and the differential gain in the amplitude characteristics of the output deteriorate with the rise of the signal level. The amplitude degradation is remarkable. In order to obtain a sufficient amount of compensation and a finely adjusted compensation characteristic, the conventional nonlinear compensation circuit is configured by independently providing nonlinear compensation circuits in multiple stages. For this reason, there is a problem that the circuit configuration is complicated and power consumption is increased, and it is difficult to reduce the size and chip.

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-linearity compensating circuit for a TV transmitter, which has a simple circuit configuration, consumes little power, and is easy to miniaturize and chip.

[0007]

In order to achieve the above object, a non-linearity compensating circuit for a TV transmitter according to the present invention comprises a first capacitor (C11) connected in series to an input signal and extracting an AC component of the input signal. ), Two resistors (R11, R12) connected to an intermediate point of the output signal of the first capacitor and applying a predetermined bias voltage to the AC component, and an AC component to which the bias voltage is applied. (TR11) that amplifies the signal at a predetermined amplification rate and outputs the amplified signal, and a diode (D
111), a resistor (R151) and a second capacitor (C111).
) Are connected in series, and at least two circuits of the black-side amplitude compensation circuit (Z11) connected in parallel with a resistor (VR111) for adjusting the bias point of the diode are connected in parallel to the output terminal of the transistor. By adjusting the bias voltage of the diode (D111) of the black-side amplitude compensation circuit (Z11), the on / off operation of the diode can be set according to the level of the input signal.

[0008]

Therefore, according to the non-linearity compensating circuit for a TV transmitter of the present invention, the amplification resistance of the signal amplifying circuit and at least two black-side amplitude compensating circuits are connected in parallel. By adjusting the bias voltage of the diode of the compensation circuit, the on / off operation of the diode can be set according to the signal level.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a non-linearity compensating circuit for a TV transmitter according to an embodiment of the present invention;

The non-linearity compensating circuit for a TV transmitter according to the embodiment shown in FIG. 1 comprises an amplifier circuit and an N-stage black-side amplitude compensating circuit connected in parallel. The amplifier circuit is a common-emitter amplifier circuit, and includes a transistor TR11 and resistors R11 to R11.
R14 and capacitors C11 and C12. Also N
The black-side amplitude compensating circuits Z11 to Z1N of the stage include a diode D111.
~ D11N, capacitors C111 ~ C11N, resistors R151 ~ R15
N, composed of variable resistors VR111 to VR11N.

In the amplifier circuit, only the AC component of the IF input signal IN is extracted by a capacitor C11 connected in series. The IF input signal via the capacitor C11 is 2
The driving voltage Vcc is divided by the resistors R11 and R12 and applied to the transistor TR11 together with the divided bias voltage. The emitter terminal of the transistor TR11 is a resistor R
Grounded via 14 to GND.

In the black-side amplitude compensation circuits Z11 to Z1N, the anode terminals of the diodes D111 to D11N at each stage are connected in parallel, and this parallel connection terminal is connected to the emitter terminal of the transistor TR11. The cathode terminals of the diodes D111 to D11N are connected in series with the resistors R151 to R15N and the capacitors C111 to C11N, and the other terminal of the capacitors C111 to C11N is connected to the G terminal.
Connected to ND. A series connection terminal of the resistors R151 to R15N and the capacitors C111 to C11N is connected to an intermediate terminal of the variable resistors VR111 to VR11N connected between the driving power supply Vcc and GND. According to this circuit configuration, by adjusting the resistance values of the variable resistors VR111 to VR11N, the diode D
The bias voltage value between the terminals 111 to D11N changes, and the on / off operation level of the diodes D111 to D11N can be adjusted. Further, the impedance values of the black-side amplitude compensation circuits Z11 to Z1N when the diodes D111 to D11N are on can be adjusted by the resistance values of the resistors R151 to R15N.

The operation of the black-side amplitude compensation circuit having the above circuit configuration will be described below. The amplification degree G of the amplifier circuit is represented by a resistance (collector resistance) R13 grounded on the collector side,
A resistor (emitter resistor) Re grounded on the emitter side
And is determined by Therefore, when the diode is off, the emitter resistance Reoff is as follows: Reoff = R14 (1) The amplification degree Goff is as follows. Goff = R13 / Reoff = R13 / R14 (2)

When the diode is on, all IF signals at the base of the transistor are made conductive. Assuming that the resistance value of the diode in this case is Rd, the emitter resistance Reon is given by: Reon = 1 / {1 / R14 + 1 / (Rd + R151)} (3). ) Is as follows. Gon = R13 / Reon = R13 ｛1 / R14 + 1 / (Rd + R
151)｝ (4) Equation (4) has the following relationship, so Gon = Goff + R13 / (Rd + R151) Obviously, Gon> Goff, and the amplification increases.

Next, a resistor R connected in series with the diode
The selection of the resistance values of 151 to R15N and the conduction operating point of the diode are adjusted by the variable resistors VR111 to VR11N. FIGS. 2, 3 and 4 show examples of setting the amplification characteristics by this adjustment.

FIGS. 2 and 3 show a black-side amplitude compensation circuit Z11.
FIG. 7 is a diagram for explaining the operation characteristics of each stage of the steps from Z1N to Z1N. The point X of the input voltage in FIG. 2 represents the operating point of the diode. The amplification degree G of the amplifier circuit is Goff in the region where the input voltage is equal to or lower than the point X, and is Gon in the region where the input voltage is equal to or higher than the point X.
In this characteristic, when the amplification resistances R13 and R14 are kept constant, the amplification characteristic at the amplification degree Gon changes depending on the resistance values of the resistors R151 to R15N connected in series with the diode, and the slope can be determined. Also, the variable resistors VR111 to VR111
By adjusting the midpoint of R11N, the diode D111
The bias voltage to D11N changes. Therefore, the operating point X can be freely selected and set as shown in FIG.

A resistor R151 connected in series with the diode
Black side amplitude compensating circuits Z11 to Z1 having different resistance values of.
By connecting N in parallel in several stages and adjusting the point X of each circuit with the variable resistors VR111 to VR11N, it is possible to obtain a curved gain characteristic. FIG. 4 shows an example of setting amplification characteristics when three stages of black-side amplitude compensation circuits Z11 to Z13 are used. The operating points X1, X2, and X3 are the ON operating points of the diodes of the respective black-side amplitude compensation circuits Z11, Z12, and Z13. The amplification characteristic line A1 is when the diode of the black-side amplitude compensation circuit Z11 is on, the amplification characteristic line A2 is when the diode of the black-side amplitude compensation circuits Z11 and Z12 is on, and the amplification characteristic line A3 is on the black side. Each of the amplitude compensation circuits Z11, Z12, and Z13 represents an ON operation of a diode.

As described above, in the present invention, in the amplitude compensation characteristic, in a transistor amplifying circuit having a self-bias circuit, the entire individual compensating circuits are arranged in multiple stages in parallel. For this reason, power consumption is small, and miniaturization and chip formation can be achieved. Further, there is an effect that the amplitude compensation circuit on the black side can be sufficiently performed. Therefore, TVs using video stage amplifiers
Applicable to transmitters.

Although the above embodiment is an example of a preferred embodiment of the present invention, the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, the circuit configuration of the amplifier circuit is not limited to the grounded-emitter circuit of the above embodiment, but may be another circuit configuration such as a grounded-collector circuit. Further, the amplifying element is not limited to the transistor of the embodiment, and an operational amplifier can be used.

[0020]

As is apparent from the above description, the non-linearity compensating circuit for a TV transmitter according to the present invention includes a diode on / off circuit of a black-side amplitude compensating circuit connected in parallel with an amplifying resistor of a signal amplifying circuit. To set the OFF operation level in multiple stages,
By adjusting the on / off operation point and the resistance value, it is possible to arbitrarily adjust the gain characteristic of the amplifier circuit. Further, this circuit can be configured by a simple circuit, power consumption is reduced, and miniaturization and chip formation are facilitated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a nonlinearity compensating circuit for a TV transmitter according to the present invention.

FIG. 2 is a gain characteristic diagram for explaining a compensation operation of the nonlinearity compensation circuit for the TV transmitter of FIG. 1;

FIG. 3 is a gain characteristic diagram for explaining a compensation operation of the nonlinearity compensation circuit for the TV transmitter in FIG. 1;

FIG. 4 is a gain characteristic diagram showing a setting example of a compensation operation of the nonlinearity compensation circuit for the TV transmitter in FIG. 1;

FIG. 5 is a diagram illustrating a characteristic example of a video signal output from a TV transmitter when no compensation processing is performed.

FIG. 6 is a diagram showing white-black characteristics with respect to the signal level of the video signal not subjected to the compensation processing in FIG. 5;

FIG. 7 is a circuit diagram showing a configuration example of a conventional nonlinearity compensation circuit for a TV transmitter.

[Description of Signs] C11, C12, C111-C11N Capacitor D111-D11N Diode R11-R14, R151-R15N Resistance TR11 Transistor VR111-VR11N Variable Resistor Z11-Z1N Black Side Amplitude Compensation Circuit

Claims (3)

(57) [Claims] 1. A first capacitor (C11) connected in series to an input signal for extracting an AC component of the input signal, and an output signal of the first capacitor is connected to an intermediate point and is predetermined as the AC component. Apply a predetermined bias voltage 2
Resistors (R11, R12), a transistor (TR11) for amplifying and outputting the AC component to which the bias voltage is applied at a predetermined amplification factor, a diode (D111), a resistor (R151) and a second A capacitor (C111) is connected in series, and a resistor (VR111) for adjusting the bias point of the diode is connected in parallel. And a diode (D111) of the black-side amplitude compensation circuit (Z11).
Wherein the on / off operation of the diode can be set according to the level of the input signal by adjusting the bias voltage of the non-linearity compensation circuit for a TV transmitter. 2. The non-linearity compensating circuit for a TV transmitter according to claim 1, wherein said resistor (VR111) is a variable resistor. 3. The variable resistor output terminal of the variable resistor (VR111) is connected to the connection point where the resistor (R151) and the second capacitor (C111) are connected in series. The TV according to claim 2, wherein
Non-linearity compensation circuit for transmitter.