Sample/hold apparatus with small-sized capacitor and its driving method
View Patent ↗A sample/hold apparatus includes first, second and third power supply terminals to which first, second and third power supply voltages are applied. The second power supply voltage is an intermediate voltage between are first and third power supply voltages. A sampling switching element is adapted to pass an input voltage at an input terminal therethrough in response to a sample/hold voltage at a sample/hold terminal. A capacitor has a first terminal connected to an output of the sampling switching element and a second terminal connected to the second power supply terminal. A buffer amplifier is adapted to perform an impedance conversion upon a voltage at the first terminal of the capacitor to generate an output voltage at an output terminal. The buffer amplifier is powered by the first and third power supply voltages.
1. A data line driver for driving a data line in a liquid crystal display apparatus comprising:
a gradation voltage generating circuit adapted to generate a plurality of positive-side voltages and a plurality of negative-side voltages;
a positive-side decoder adapted to select one of said positive-side voltages in accordance with a video data signal in response to a first polarity signal;
a negative-side decoder adapted to select one of said negative-side voltages in accordance with said video data signal in response to a second polarity signal;
a sample/hold circuit connected to said positive-side decoder, said negative-side decoder and said data line, said sample/hold circuit selectively sampling and holding output signals of said positive-side decoder and said negative-side decoder; and
an intermediate voltage generating circuit connected to said sample/hold circuit, said intermediate voltage generating circuit being adapted to generate an intermediate voltage among said positive-side voltages and said negative-side voltages;
said sample/hold circuit comprising:
a first sampling switching element connected to the output of said positive-side decoder, said first sampling switching element being adapted to sample the selected one of said positive-side voltages in response to a first sample/hold signal;
a second sampling switching element connected to the output of said negative-side decoder, said second sampling switching element being adapted to sample the selected one of said negative-side voltages in response to a second sample/hold signal;
a first capacitor connected between an output of said first sampling switching element and an output of said intermediate voltage generating circuit;
a second capacitor connected between an output of said second sampling switching element and the output of said intermediate voltage generating circuit;
a first transfer switching element connected between the output of said first sampling switching element and a node, said first transfer switching element being turned ON in response to a first control signal analogous to said second polarity signal;
a second transfer switching element connected between the output of said second sampling switching element and said node, said second transfer switching element being turned ON in response to a second control signal analogous to said first polarity signal; and
a buffer amplifier connected between said node and said data line.
2. The data line driver as set forth in claim 1 further comprising a reset switching element connected between said node and the output of said intermediate voltage generating circuit, said reset switching element being turned ON in response to a reset signal generated at rising and falling edges of said first and second polarity signals.
3. The data line driver as set forth in claim 1 , wherein said intermediate voltage generating circuit comprises a voltage divider for receiving a minimum one of said positive-side voltages and a maximum one of said negative-side voltages.
4. The data line driver as set forth in claim 3 , wherein said voltage divider includes a series of two resistors whose values are the same.
5. The data line driver as set forth in claim 1 , wherein said intermediate voltage is applied to a common electrode of said liquid crystal display apparatus.