Apparatus for driving displays

1. An apparatus for use in driving a display, the apparatus comprising:

frame generating means arranged to generate a succession of frame pulses at regular intervals;

frame blanking generating means arranged 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 capable of being connected to a device driver; and

switching means arranged to connect the output line to one of the input lines during the portion of each regular interval when a frame blanking pulse is not present, the switching means being capable of changing the input line to which the output line is connected during successive frame periods, the switching means being arranged 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 switching means comprises a plurality of analog switches, one associated with each input line, each analog switch having a first input connected to its associated input line, an output connected to the output line, each analog switch, and a second input arranged to receive an enable signal, one value of the enable signal causing the voltage on the associated 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 the drain of the which receives the signal from its associated input line;

a second transistor having a drain connected to the output line;

a connector interconnected the sources of the first and second transistors;

an RC circuit connected between the connector and the gates of the first and second transistors;

first and second resistors arranged in series between the gates of the first and second transistors and ground; and

a third transistor arranged to receive the enable signal, and connected between ground and between the first and second resistors.

4. An apparatus according to claim 3 having a negative voltage on its associated input line, wherein the first and second transistors are N-channel transistors, and the third transistor has its one of its emitter and collector arranged to receive the enable signal, its base connected to ground and the other of its emitter and collector connected between the first and second resistors.

5. An apparatus according to claim 3 having a positive voltage on its associated input line, wherein the first and second transistors are P-channel transistors, and the third transistor has its base arranged to receive the enable signal, and its other two electrodes connected to ground and between the first and second resistors.

6. An apparatus according to claim 1 wherein the frame blanking interval is sufficiently long to allow the maximum value which can be asserted on the output line to decay below the minimum value which can be asserted on the output line within the frame blanking interval.

7. An electrophoretic display comprising an apparatus according to claim 1 .

8. An electrophoretic display according to claim 7 which is a color electrophoretic display.

9. A method of driving a display, the method comprising:

generating a succession of frame pulses at regular intervals;

generating a succession of frame blanking pulses at the same intervals as the frame pulses;

asserting a plurality of differing input voltages on a plurality of input lines providing an output line connected to a device driver;

connecting the output line to one of the input lines during the portion of each regular interval when a frame blanking pulse is not present;

connecting the output line to ground and draining charge from the output line when a frame blanking pulse is present; and

connecting the output line to a different one of the input lines after draining charge from the output line and when a frame blanking pulse is no longer present.

10. A method according to claim 9 wherein the frame blanking interval is sufficiently long to allow the maximum value which can be asserted on the output line to decay below the minimum value which can be asserted on the output line within the frame blanking interval.

11. An electrophoretic display arranged to carry out the method of claim 9 .

12. An electrophoretic display according to claim 11 which is a color electrophoretic display.