Patent ID: 6518842
Filing Date: 2003-02-11
Classification: H03F

Abstract:
A bipolar rail-to-rail input stage with a selectable transition threshold, comprising:an input stage comprising: a first differential pair comprising first and second PNP transistors having their bases connected to receive a differential input signal and arranged to conduct respective collector currents which vary with said differential input signal, said differential input signal having a common mode voltage Vcm, the emitters of said first and second PNP transistors connected together at a first common mode node, a second differential pair comprising first and second NPN transistors having their bases connected to receive said differential input signal and arranged to conduct respective collector currents which vary with said differential input signal, the emitters of said first and second NPN transistors connected together at a second common mode node, at least one tail current source circuit arranged to provide tail current to said first and second common mode nodes, a switching circuit connected to receive a transition threshold voltage Vth and arranged to make said first differential pair active when Vcmth and to make said second differential pair active when Vcm>Vth, and a transition threshold voltage selection circuit which receives a select signal at an input and which provides Vth to said switching circuit, said selection circuit arranged to provide a selectable one of at least two different Vth voltages in response to said select signal.