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Subthreshold Gm-C filters offer the low power and wide tunable range required for use in fully implantable bionic ears. The major design challenge that must be met is increasing the linear range. A capacitive-attenuation technique is presented and refined to allow the construction of wide-linear-range bandpass filters with greater than 1 Vpp swings. For a 100-200 Hz fully differential filter with second-order roll off slopes and greater than 60 dB dynamic range, experimental results from a 1.5-μm, 2.8-V BiCMOS chip yield only 0.23 μW power consumption; for a 5-10 kHz filter with the same specifications the power only increased to 6.36 μW. Fully differential filters with first-order slopes had a dynamic range of 66 dB and power consumptions of 0.12 and 3.36 μW in the 100-200 Hz and 5-10 kHz cases, respectively. We show that our experimental results of noise and linear range are in good accord with theoretical estimates of these quantities.
Date of Publication: Jan 2003