CMOS technology and current-feedback op-amps

Some of the problems related to the application of CMOS technology to current-feedback operational amplifiers (CFB op-amps) are identified. Problems caused by the low device transconductance and by the absence of matching between p-channel and n-channel transistors are examined, and circuit solutions providing improved input characteristics are presented. Problems related to the achievable output voltage swing are examined, and circuits which may be used to achieve a near rail to rail output swing are proposed. It is concluded that mere translations of bipolar circuit designs yield a rather poor performance compared to the bipolar designs, but CMOS has a potential for CFB op-amp design if more ingenious circuit configurations are applied.<>