Apparatus for driving displays
An apparatus ( 100 ) for use in driving a display, especially a color electrophoretic display comprising frame generating means generating a succession of frame pulses at regular intervals; frame blanking generating means generating a succession of frame blanking pulses at the same intervals; a plurality of input lines each arranged to receive one of a plurality of differing input voltages (Vin 1 , . . . VinN), all of the same polarity; an output line capable of being connected to a device driver ( 106 ); and switching means ( 102 A, . . . 102 N) connecting the output line to one of the input lines when no frame blanking pulse is present, the switching means ( 102 A, . . . 102 N) being capable of changing the input line to which the output line is connected during successive frame periods, the switching means ( 102 A, . . . 102 N) being arranged to drain charge from the output line when a frame blanking pulse is present.
1. An apparatus for use in driving a display, the apparatus comprising:
a frame generator configured to generate a succession of frame pulses at regular intervals;
a frame blanking generator configured to generate a succession of frame blanking pulses at the same intervals as the frame pulses;
a plurality of input lines, each input line being arranged to receive one of a plurality of differing input voltages;
an output line; and
one or more switches configured to connect the output line to a first one of the input lines during frame pulses when a frame blanking pulse is not present, the one or more switches configured to connect the output line to a second one of the input lines during successive frame periods, and the one or more switches configured to connect the output line to ground and drain charge from the output line when a frame blanking pulse is present.
2. An apparatus according to claim 1 wherein the one or more switches comprises a plurality of analog switches, each analog switch having
a first input connected to one input line,
an output connected to the output line, and
a second input configured to receive an enable signal, one value of the enable signal causing the voltage on the one input line to be asserted on the output line, and a second value of the enable signal causing the voltage on the output line to decay.
3. An apparatus according to claim 2 wherein at least one analog switch comprises:
a first transistor having a first source, a first gate, and a first drain, the first drain connected to the one input line;
a second transistor having a second source, a second gate, and a second drain, the drain connected to the output line;
a connector configured to connect the first source to the second source;
an RC circuit connected to the connector and the first and second gates;
first and second resistors arranged in series between ground and the first and second gates; and
a third transistor having a collector connected between the first and second resistors, an emitter connected to the second input, and a base connected to ground.
4. An apparatus according to claim 3 , wherein the first and second transistors are N-channel transistors.
5. An apparatus according to claim 2 wherein at least one analog switch comprises:
a first transistor having a first source, a first gate, and a first drain, the first drain connected to the one input line;
a second transistor having a second source, a second gate, and a second drain, the drain connected to the output line;
a connector configured to connect the first source to the second source;
an RC circuit connected to the connector and the first and second gates;
first and second resistors arranged in series between ground and the first and second gates; and
a third transistor having a base connected to the second input, a collector, and an emitter, one of the collector and the emitter being connected between the first and second resistors and the other of the collector and the emitter being connected to ground.
6. An apparatus according to claim 5 , wherein the first and second transistors are P-channel transistors.
7. An apparatus according to claim 1 wherein a frame blanking interval comprising the succession of frame blanking pulses is sufficiently long to allow a maximum voltage value which can be asserted on the output line to decay below a minimum voltage value which can be asserted on the output line within the frame blanking interval.
8. An electrophoretic display comprising an apparatus according to claim 1 .
9. An electrophoretic display according to claim 8 which is a color electrophoretic display.