Turn-on bus transmitter with controlled slew rate

Abstract

An amplifier/driver () for a bus has an output transistor (M) that is controlled by a controlled current source (I). In a quiescent state, the output transistor is configured as part of a current mirror (M, M) that maintains a gate-source voltage on the output transistor above the threshold voltage of the output transistor, thereby providing a fast turnon turn-on time. In an active state, the controlled current source provides a substantially constant current to the output transistor to achieve a controlled slew-rate, then reduces the current to the output transistor when a desired output voltage level is achieved. To improve power efficiency, a second controlled current source (I) provides current to the output load when the desired output voltage level is achieved. To minimize transients, a class-AB control circuit () provides a minimum bias current to the output transistor, to prevent it from turning off when the desired output voltage level is achieved.