Digital logic protocol interface for different semiconductor technologies

Abstract

A method and apparatus for implementing silicon logic interface protocols in compound semiconductor technology converts the voltages corresponding to standard logic digital values to voltages appropriate to these digital values in compound semiconductor technology, and vice versa. In an input buffer circuit of the present invention, the voltage of the converted logic level depends only on the difference between the input standard voltage level and a reference voltage which corresponds to the threshold voltage of silicon logic so that the converted voltage is independent of device process, circuit temperature, and power supply output variations to first order. A source follower input is used so that the driving logic circuit need not source current to or sink current from the input buffer circuit so that fanout is not limited. An output buffer circuit of the present invention achieves a stable output buffer tri-state functionality and eliminates leakage current problems by a modification of a standard totem pole output configuration. A standard totem pole type output is modified to use a second pull-down MESFET which puts the source of the first pull-down MESFET at a small positive voltage. As a result, the gate-source diode of the first pull-down MESFET is reverse biased, shutting the first pull-down MESFET off hard.