Attenuation-Predistortion Linearization of CMOS OTAs With Digital Correction of Process Variations in OTA-C Filter Applications
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An architectural attenuation-predistortion linearization scheme for a wide range of operational transconductance amplifiers (OTAs) is proposed and demonstrated with a transconductance-capacitor (Gm-C) filter. The linearization technique utilizes two matched OTAs to cancel output harmonics, creating a robust architecture. Compensation for process variations and frequency-dependent distortion based on Volterra series analysis is achieved by employing a delay equalization scheme with on-chip programmable resistors. An OTA design with the proposed broadband linearization method has third-order inter-modulation (IM3) distortion better than -74 dB up to 350 MHz with 0.2 pp input, 70 dB signal-to-noise ratio (SNR) in 1 MHz bandwidth, and 5.2 mW power consumption. The distortion-cancellation technique enables an IM3 improvement of up to 22 dB compared to a commensurate OTA without linearization. A proof-of-concept low-pass filter with the linearized OTAs has a measured IM3 <-70 dB and 54.5 dB dynamic range over its 195 MHz bandwidth. The standalone OTAs and the filter were fabricated on a 0.13 m CMOS test chip with 1.2 V supply. 2006 IEEE.
