APPARATUS AND METHOD FOR SHIFTING A SIGNAL FROM A FIRST REFERENCE LEVEL TO A SECOND REFERENCE LEVEL

摘要

A level-shifting apparatus 80 includes an input section 82, level shift sections 84 and output sections 86. Differential signaling input signals received from an upstream data source at input terminals 100, 102 of input section 82 are coupled with respective bases of common emitter NPN bipolar transistors Q1, Q2 and respectively presented at collector outputs 124, 126 to level shift sections 84. Each level shift section 84 includes a low speed network 130 and a high speed network 140 coupled substantially in parallel between a respective output 124, 126 and an output locus 88. Low speed network 130 operates as a level setting signal path to set the DC (direct current) level at output locus 88 to a desired level. Low speed network 130 employs an active amplifier component to set output DC resistance. In one embodiment, the active component is an NPN bipolar transistor Q4 configured as an emitter-follower, with its base connected to an output 124, 126 via a resistor RLS. High speed network 140 operates as a signal transition path to speed up provision of signal transitions (for example, information bearing signal transitions) to output locus 88. In one embodiment, a base 142 of an NPN bipolar transistor Q5 is driven without added series resistance to avoid delay and unwanted filtering. Output section 86 connects signals appearing at output locus 88 with downstream portions of a communication system.