Circuit with voltage clamping for bias transistor to allow power supply over-voltage

摘要

A ring oscillator stage includes two differential transistor pairs configured to add an adjustable amount of delay to a differential input signal. Each differential pair is biased with a bias current transistor; the bias current transistor is "protected" by a voltage-clamping transistor that limits the drain voltage of the bias current transistor. The voltage-clamping transistors enable use of a power supply voltage (V_DD) that would otherwise exceed the reliability breakdown voltage limit of the bias current transistors.