A Practical Micropower Programmable Bandpass Filter for Use in Bionic Ears

Subthreshold 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 pp 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 1.5m, 2.8-V BiCMOS chip yield only 0.23 m power consumption; for a 5–10 kHz filter with the same specifications the power only increased to 6.36 W. Fully differential filters with first-order slopes had a dynamic range of 66 dB and power consumptions of 0.12 and 3.36 W 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.