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

Abstract

A continuous-time common-mode feedback circuit (CMFB) is presented. A two-stage high-gain architecture is used to minimize the offset of the common-mode voltage. A special compensation scheme enables this circuit to be used in high-impedance current-mode systems without a stability problem. Simulation and testing results show the superior performance of this circuit. It is proven to be an ideal common-mode feedback circuit for systems which require an accurate and stable commonmode voltage. This circuit has been implemented in a continuous-time switched-current modulator with a 2m CMOS process. With a 50MHz clock, the modulator has achieved a 60dB dynamic range in a 1MHz bandwidth.

Design of a 4th-Order Feed-Forward-Compensated Operational Amplifier for Multi-GHz Sampling Frequency Continuous-Time Bandpass Sigma-Delta Modulators

“…The PMOS transistors in stages two to four are divided into two to accommodate the CMFB voltage. Common-mode correction based on RC networks is used in stages two and four, while stage three features a broadband CMFB amplifier [8]. A pair of cross-coupled capacitors in stages one and two help in improving the phase margin of the amplifier.…”

A low distortion CMOS continuous‐time common‐mode feedback circuit

“…A differential-difference amplifier (DDA) CMFB circuit that uses two differential pairs is shown in Figure 1 [13]. The advantage of the DDA CMFB circuit is having a larger transconductance, Gm, compared with the resistor-averaged CMFB circuit [7]. However, some undesired distortion is induced by the nonlinear i-v characteristic of MOS transistors in the DDA CMFB circuit, may actually be introduced into the CM control signal [14].…”

Optimization of Delta-Sigma ADC for Column-Level Data Conversion in CMOS Image Sensors

“…Since it can offer enough swing and linearity with a small area, a differential-difference amplifier CMFB (DDA-CMFB), which is a continuous-time CMFB, is used in the main OTA [9]. Figure 3 shows the structure of the DDA-CMFB circuit.…”