Patent ID: 6611155
Filing Date: 2003-08-26
Classification: H03F

Abstract:
An output driver circuit of a serial bus structure directly coupled to a cable in a system for digital data transfer to and from the cable over the bus structure, the output driver circuit having a power supply rail and ground, comprising:a current source; a first sub-circuit portion having a reference voltage node, the first sub-circuit portion coupled to the current source; a second sub-circuit portion coupled to the current source, the second sub-circuit portion having an external voltage bias node and a common mode voltage node, the external voltage bias node coupled to the cable; a switch coupled between the first and second sub-circuit portions to provide an internal voltage bias operation mode and an external voltage bias operation mode for the output driver circuit, the switch having a reference voltage input, an internal bias voltage input, a common mode voltage input and a pair of outputs, the reference voltage input coupled to the reference voltage node, the common mode voltage input coupled to the common mode voltage bias node; and an amplifier having a positive and a negative input and an output, each coupled to a respective one of the pair of outputs of the switch to amplify the difference between the internal bias voltage and the common mode voltage in the internal voltage bias operation mode and to amplify the difference between the reference voltage and the common mode voltage in the external voltage bias operation mode, the output coupled to the first and second sub-circuit portions to provide the amplified difference to the first and second sub-circuit portions.