Charge pump circuit

Abstract

Adverse effects of switching noise produced by a charge pump circuit on a displayed image are prevented. In a synchronizing separation circuit 18, a synchronizing signal is separated from a video signal. The separated synchronizing signal is subjected to 1 / 2 frequency division in a flip-flop 20 to obtain a clock signal having a period which is two times as much as one horizontal period, and this clock signal is utilized to control switching of the charge pump circuit. As a result, a timing at which each switch in the charge pump is changed over can be set in a period close to a horizontal synchronizing signal without a video signal, thereby preventing noise from affecting the video signal.

Description

technical field [0001] The present invention relates to a charge pump circuit for obtaining an output voltage by varying a power supply voltage by utilizing the charging voltage of a charged capacitor. Background technique [0002] Conventionally, charge pump circuits have been used in various circuits. In particular, in various portable devices, the power supply voltage is limited in order to utilize battery power. On the other hand, various circuits are required to use as high a power supply voltage as possible in order to facilitate operation. Here, a charge pump circuit is often used to boost the voltage of the battery power supply. Regarding such a charge pump circuit using a capacitor, there are, for example, descriptions in Patent Document 1 and the like. In addition, a negative power supply is sometimes required for circuit operation, and in such a case, a charge pump circuit is also used. [0003] [Patent Document 1] JP-A-7-298607 [0004] Here, in such a charg...

AI Technical Summary

Problems solved by technology

[0004] Here, in such a charge pump circuit, in the switch that controls the charge to the capacitor and the switch, especially when the switch is turned on, there is a large current change for a short time, which may cause a series connection to the power supply or noise problem

[0005] In particular, if such noise is strung into a video signal for display on a monitor, there are problems manifested in the display

As the above-mentioned switching signal, in the case of using a video signal and an asynchronous signal, it is considered that there is little practical harm. The timing of the screen, there is a problem with the impression of the twill pattern

If a horizontal synchronous signal or the like is used for the switching signal of the switch of the charge pump circuit at the position of the display screen, there is a problem that noise will be inserted in a specific position and vertical lines will be generated on the display of the monitor.

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