Abstract:

Flat panel displays require buffers for column driving circuits. These buffers have unity gain and usually drive large capacitive loads. To maintain the railto- rail swing operation, most of the buffer circuits employ complementary differential pair input stage. Whenever the input voltage is close to supply voltages, one of the driving paths enters the cut-off state. In this paper, a novel adaptive biasing technique for biasing differential input pair transistors is proposed in order to maintain high driving capacity for the whole input range. In the proposed scheme, whenever an NMOS input stage enters the cut-off stage, the biasing current is boosted for the PMOS input stage and vice versa. As a result, without increasing the biasing current, driving capability of the circuit is boosted in the ranges which are close to the supply voltages. With the proposed biasing scheme, the circuit consumes 45% less biasing current with 16% better settling time as compared to the non-adaptive biased circuit. The proposed biasing circuit and liquid-crystal displays (LCD) buffer is designed using 0.35 μm AMS technology and the SPICE results are reported. The circuit provides high slew-rate and good settling time characteristics which is comparable to the state-of- art LCD driving circuits.

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