Fully-differential CMOS current-mode circuits

A CMOS fully-differential current-mode analog signal processing technique has been developed. The basic building block, a 5-V fully differential current-mode operational amplifier (I-OPAMP), has been integrated using the MOSIS 2 mu m n-well CMOS technology. Measured total harmonic distortion (THD) is -70 dB with a peak signal to bias current ratio of 0.5. By simply adding MOS switches, the I-OPAMP topology is easily extended to implement fully differential switched-current (SI) circuits with first-order cancellation of clock-feedthrough effects. A five-pole Chebyshev lowpass fully differential SI ladder filter has also been integrated in the 2- mu m p-well CMOS technology. Measured results show that, with a sampling frequency of 128 kHz, the desired ripple bandwidth of 5 kHz is accurately realized using the fully differential SI structure. Dynamic range is greater than 80 dB with a power dissipation of 14 mW.<
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