A continuous-time common-mode feedback circuit (CMFB) for high-impedance current-mode applications

A continuous-time common-mode feedback circuit (CMFB) is presented. A two-stage high-gain architecture is used to stabilize and minimize the offset of the common-mode voltage. A long-channel differential-difference amplifier (DDA) input stage enables this CMFB circuit to have a wide input voltage range without a serious linearity problem. A special compensation scheme enables this circuit to be used in high-impedance current-mode systems without a stability problem. This circuit has been implemented within a continuous-time switched-current /spl Sigma//spl Delta/ modulator in a 2 /spl mu/m CMOS process. It achieves a /spl plusmn/1 V input voltage range with an active area of 100 /spl mu/m/spl times/60 /spl mu/m and a power dissipation of 270 /spl mu/W from a single 5 V power supply.