JP4896812B2 - Video circuit - Google Patents

Description

  The present invention relates to a video circuit including a video processing circuit and a charge pump circuit. In particular, when a negative voltage generated by the charge pump circuit is used as a negative power supply voltage of the video processing circuit, the negative voltage includes noise. The present invention relates to a video circuit that prevents deterioration of video signal quality and reduces power consumption.

  FIG. 4 shows a configuration of a conventional video circuit that supplies the negative voltage generated by the charge pump circuit to the video processing circuit as a negative power supply voltage. The video processing circuit 10 includes a clamp circuit 11 that clamps a sync chip and a pedestal level of an input video signal including a synchronization signal, and various image processing (hue adjustment, contrast adjustment, video signal output from the clamp circuit 11). A video signal processing circuit 12 for performing enlargement, reduction, edge enhancement, and other processing), and an output drive circuit 13 that amplifies the output signal of the video signal processing circuit 12 to a video drive signal and supplies the amplified signal to, for example, a 75Ω load. The output drive circuit 13 is supplied with a positive power supply voltage + V and a negative power supply voltage −V as power supplies in order to expand the dynamic range and reduce the output capacity. C1 is a DC cut capacitor, and C2 is a negative voltage supply capacitor. The positive power supply voltage + V and the ground voltage GND are applied to the clamp circuit 11 and the video signal processing circuit 12.

  Reference numeral 50 denotes an oscillation circuit that generates a pulse having a frequency of around 100 KHz. A charge pump circuit 20 receives an oscillation signal output from the oscillation circuit 50, generates a negative voltage -V in cooperation with the capacitor C2, and supplies the negative voltage -V to the output drive circuit 13 of the video processing circuit 10.

  As shown in FIG. 6, the charge pump circuit 20 includes a charging capacitor C3, the capacitor C2, and the switches SW1 to SW4. When the output of the oscillation circuit 50 is at the H level, the switches SW1 and SW2 are turned off and the switch SW3 is turned on. , SW4 are turned on, and when they are at the L level, the switches SW1, SW2 are turned on, and the switches SW3, SW4 are turned off. As a result, the capacitors C2, C3 are charged with the charges of the polarity shown in FIG. (See FIG. 5).

  On the other hand, using an oscillation circuit, a synchronization signal is extracted from an input video signal, a continuous pulse is generated based on the synchronization signal, and this continuous pulse is input to a charge pump circuit to generate a negative voltage. There is an amplifier described in Patent Document 1 in which a negative voltage is supplied to a main amplifier (corresponding to the output drive circuit 13 in FIG. 4).

According to the video circuit shown in FIG. 4 and Patent Document 1 described above, since the positive power supply voltage + V and the negative power supply voltage −V are applied to the output driving circuit 13 and the amplifier, the dynamic range is expanded and the output capacity is reduced. Can be planned.
JP 2005-151468 A

  However, in the video circuit of FIG. 4, the switches SW1 to SW4 of the charge pump circuit 20 are continuously turned on / off based on the oscillation signal generated by the oscillation circuit 50, so that the generated negative voltage −V In the video period of the input video signal, noise and ripple are superimposed, and the influence appears in the output video signal, so that beat noise or the like is generated on the screen.

  Also in the amplifier of Patent Document 1, since the charge pump circuit is driven by continuous pulses, the noise and ripple are superimposed on the output video signal and beat noise on the screen, as in the video circuit of FIG. 4 described above. Etc. will be generated.

  Furthermore, the video circuit of FIG. 4 and the amplifier of Patent Document 1 have a problem that power consumption is large because the charge pump circuit is always operating.

  An object of the present invention is to provide a video circuit that improves the quality of an output video signal and minimizes power consumption by preventing noise and ripple from being superimposed on the supplied negative voltage as much as possible.

In order to achieve the above object, a video circuit according to a first aspect of the present invention is a video circuit provided with a first capacitor for a negative voltage power source required for a video processing circuit . A capacitor is provided, and the plurality of switches are set to a first switching state to charge the second capacitor with a positive power supply voltage, and the charging of the first capacitor is stopped. By setting the second switching state opposite to the first switching state, the first capacitor is charged with the voltage of the second capacitor, and the first capacitor generates a negative voltage. A charge pump circuit that stops the charging of the positive power supply voltage to the second capacitor, a voltage detection circuit that detects the negative voltage of the first capacitor, and a voltage detection circuit that detects the negative voltage. When the negative voltage reaches a lower limit value, the plurality of switches of the charge pump circuit are set to the first switching state to cause the second capacitor to be charged with the positive power supply voltage and detected by the voltage detection circuit When the negative voltage thus reached reaches an upper limit value higher than the lower limit value, the voltage of the second capacitor is set to the first voltage by setting the plurality of switches of the charge pump circuit to the second switching state. And a control circuit for charging the capacitor .

  According to the present invention, the charge pump circuit does not resume operation until the output negative voltage reaches the upper limit value, so that noise and ripple can be suppressed as much as possible, and power consumption can be reduced.

<First embodiment>
FIG. 1 is a block diagram showing the configuration of a video circuit according to the first embodiment of the present invention, and FIG. 2 is an operation waveform diagram thereof. Similar to the configuration of FIG. 4, the video processing circuit 10 includes a clamp circuit 11 for clamping the sync chip and pedestal level of the input video signal including the synchronization signal, and various images for the video signal output from the clamp circuit 11. A video signal processing circuit 12 to which processing (hue adjustment, contrast adjustment, enlargement, reduction, edge enhancement, and other processing) is applied, and an output signal of the video signal processing circuit 12 is amplified to a video drive signal and supplied to, for example, a 75Ω load The output drive circuit 13 is provided. The output drive circuit 13 is supplied with a positive power supply voltage + V and a negative power supply voltage −V as power supplies in order to expand the dynamic range and reduce the output capacity. C1 is a DC cut capacitor, and C2 is a negative voltage supply capacitor. The positive power supply voltage + V and the ground voltage GND are applied to the clamp circuit 11 and the video signal processing circuit 12.

  The charge pump circuit 20 has the circuit configuration shown in FIG. 6 described above, and generates a negative voltage −V in the capacitor C2 by turning on / off the switches SW1 to SW4.

  Reference numeral 30 denotes a voltage detection circuit which inputs a negative voltage charged in the capacitor C2 and detects an upper limit value -V1 and a lower limit value -V2. Note that -V2 <-V1, -V1 <0, and -V2 <0. For example, if + V = 5V, −V = −5V, −V2 = −5V, and −V1 = −4V.

  Reference numeral 40 denotes a control circuit. When the upper limit value −V1 is detected by the voltage detection circuit 30, the switches SW1 and SW2 of the charge pump circuit 20 are turned off, the switches SW3 and SW4 are turned on, and the capacitor C3 is charged. The charged electric charge is supplied to the capacitor C2. As a result, the capacitor C2 is charged all at once in the direction of increasing the negative voltage. When the lower limit value V2 is detected, the switches SW1 and SW2 of the charge pump circuit 20 are turned on and the switches SW3 and SW4 are turned off to supply charges to the capacitor C3. As a result, the capacitor C2 is disconnected from the charge pump circuit 20.

  Therefore, since the capacitor C2 for supplying a negative voltage is charged only during the period when the charging voltage reaches the lower limit value -V2 after the upper limit value -V1 is reached, it is negative compared to the conventional example in which charging is repeated continuously. Noise components such as ripples appearing in the voltage −V are reduced. In addition, since the capacitor C2 is charged only when necessary, power consumption is also reduced.

<Second embodiment>
FIG. 3 is a block diagram showing the configuration of the video circuit according to the second embodiment of the present invention. Here, the control circuit 40 controls the operation / stop of the oscillation circuit 50 shown in FIG. That is, when the upper limit value −V1 is detected by the voltage detection circuit 30, the control circuit 40 operates the oscillation circuit 50, and when the lower limit value −V2 is detected, the oscillation circuit 50 is stopped. In this case, when the oscillation circuit 50 is stopped, the switches SW1 to SW4 of the charge pump circuit 20 may be in a state where the switches SW1 and SW2 are on and the switches SW3 and SW4 are off or vice versa.

<Other examples>
In each of the above embodiments, the negative voltage generated by the charge pump circuit 20 and the capacitor C2 is supplied only to the output drive circuit 13 of the video processing circuit 10. However, when the video signal processing circuit 12 is a positive and negative power source system. Also supply there. Further, the charge pump circuit 20 is not limited to the circuit configuration of FIG. 6, and various circuit types can be applied.

It is a block diagram which shows the structure of the video circuit of 1st Example of this invention. FIG. 2 is an operation waveform diagram of the video circuit in FIG. 1. It is a block diagram which shows the structure of the video circuit of the 2nd Example of this invention. It is a block diagram which shows the structure of the conventional video circuit. FIG. 5 is an operation waveform diagram of the video circuit in FIG. 4. It is a circuit diagram of a charge pump circuit.

Explanation of symbols

10: Video processing circuit, 11: Clamp circuit, 12: Video signal processing circuit, 13: Output drive circuit, 20: Charge pump circuit, 30: Voltage detection circuit, 40: Control circuit, 50: Oscillation circuit

Claims (1)

In the video circuit provided with the first capacitor for the negative voltage power source required for the video processing circuit,
A plurality of switches and a second capacitor are provided, and a positive power supply voltage is charged to the second capacitor by stopping the charging of the first capacitor by setting the plurality of switches to the first switching state. Then, by setting the plurality of switches to a second switching state opposite to the first switching state, the voltage of the second capacitor is charged to the first capacitor and negatively charged to the first capacitor. A charge pump circuit that generates a voltage and stops charging the positive power supply voltage to the second capacitor;
A voltage detection circuit for detecting the negative voltage of the first capacitor;
When the negative voltage detected by the voltage detection circuit reaches a lower limit value, the second capacitor is charged with the positive power supply voltage by setting the plurality of switches of the charge pump circuit to the first switching state. When the negative voltage detected by the voltage detection circuit reaches an upper limit value that is higher than the lower limit value, the plurality of switches of the charge pump circuit are set to the second switching state. A control circuit for charging the voltage of the capacitor to the first capacitor;
Video circuit, characterized in that it comprises a.

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