| This thesis investigates high performance transconductors for Transconductance-capacifor (Gm-C) circuits in Silicon-Germanium (SiGe) CMOS process. The transconductors are designed to be linear with the input signals resulting in low distortion. The linearization of the transconductors is achieved by using a method, called Constant Transconductance technique. This method is based on the square-law of MOSFETs, and results in near constant tranconductance when the MOSFETs of the input stages of the transconductor work in the saturation range. Three types of transconductors are developed and their aspects are analyzed and verified through simulation; the first one is for low supply voltage, named Low-Voltage Transconductor; the second one is for high common mode range (CMR) of the circuits, named High CMR Transconductor; and the third one is for very low distortion, named Very Low-Distortion Transconductor.; In order to demonstrate the efficacy of the Constant Transconductance technique, three fully-differential, 4th order, C-case, elliptic lowpass filters are designed and simulated based on the Low Voltage Transconductors, the High CMR Transconductors and the Very-low Distortion Transconductors, respectively. Two of them, the High CMR Filter and the Very-low Distortion Filter have been fabricated and measured. The filters are designed for a cut-off frequency of 2MHz, consuming 0.48mW for Low Voltage filter, 0.86mW for High CMR filter and 1.90mW for Low Distortion filter, respectively. The experimental results for the power dissipation are 1.06mW for High CMR filter and 2.02 mW for the Very-low Distortion Filter at a cut-off frequency of 2MHz. The filters also show good total harmonic distortion of −51.9dB for Low Voltage filter, −55.6dB (measured −53.14dB) for high CMR filter and −64.3dB (measured −62.48dB) for Very Low-Distortion filter when in-band voltage signals' amplitude are 100mVp-p. This confirms that the low power and low distortion performance has been achieved for the filters. |
