Patent ID: 7005921
Filing Date: 2006-02-28
Classification: H03F

Abstract:
1. A common-mode feedback circuit for a fully-differential operational amplifier device, the circuit comprising: a first power supply input terminal for connecting to a first voltage potential; a second power supply input terminal for connecting to a second voltage potential; a first input terminal for connecting to a non-inverting output of said fully-differential operational amplifier device; a second input terminal for connecting to an inverting output of said fully-differential operational amplifier device; an output terminal for providing a common-mode feedback voltage; bridging said first power supply terminal Vdd and said second power supply input terminal, first means for establishing a substantially constant bias current; connected to said first means, to said first input terminal and said second input terminal, and to said second power supply input terminal, second means for changing division of said substantially constant bias current when signals to said first input terminal and said second input terminal are not in equilibrium; bridging said first power supply input terminal and said second power supply input terminal and connected to said first means and said second means, third means for setting common-mode feedback voltage level at said output terminal, and wherein said bias current is shared between said second means and said third means such that when inverting output and non-inverting output of said fully-differential operational amplifier device are not in equilibrium said bias current through said third means is changed via said second means wherein said third means provides said common-mode feedback reference voltage at a level for re-balancing said fully-differential operational amplifier device.