Patent ID: 7348810
Filing Date: 2008-03-25
Classification: H03F,H04L

Abstract:
1. An integrated circuit apparatus for differential signal output, comprising: an output driver circuit, providing positive and negative currents to differential output pins, which currents are derived from equivalent current source transistors connecting to positive and negative supply rails; a reference circuit branch, receiving an input reference current and developing a first reference voltage; a first matched circuit stack, between the positive and negative supply rails, containing a first branch that is a ratioed replica of the reference circuit branch in series with a second branch that is a ratioed replica of a first current path of the output driver, the second branch containing a controlled current source transistor, with the first matched circuit stack developing a second reference voltage at the junction of its two branches; a first differential amplifier that develops as an output a gain-multiplied value of the difference between the first reference voltage and the second reference voltage, this output connecting to the control input of the controlled current source transistor of the second branch of the first matched circuit stack and to the control input of the current source transistor of the first current path of the output driver; a second matched circuit stack, between the positive and negative supply rails, containing a third branch that is a ratioed replica of a second current path of the output driver in series with a fourth branch that is a ratioed replica of the first current path of the output driver, the fourth branch matched exactly with the second branch of the first matched circuit stack and containing a current source transistor with its control input connecting to the output of the first differential amplifier, the third branch containing a controlled current source transistor, with the second matched circuit stack developing a third reference voltage at the junction of its two branches; a second differential amplifier that develops as an output a gain-multiplied value of the difference between the second reference voltage and the third reference voltage, this output connecting to the control input of the controlled current source transistor of the third branch of the second matched circuit stack and to the control input of the current source transistor of the second current path of the output driver.