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Low-Voltage Low-Power Filters with Independent ω0 and Q Tuning for Electronic Cochlea Applications

An acoustic second-order low-pass filter is proposed for filter banks emulating the operation of a human cochlea. By using a special filter structure and an innovative quality (Q)-factor tuning technique, an independent change of the cutoff frequency (ω0) and the Q-factor with unchanged gain at low frequencies is achieved in this filter. The techniques applied result in a simple filter design with low Q-factor sensitivity to component mismatch. These filter features greatly simplify the implementation of the electronic cochlea in CMOS technologies. An exemplary filter bank designed and simulated in an X-FAB 180 nm CMOS process is presented, which consumes 1.25–34.75 nW of power per individual filter when supplied with 0.5 V. The 11-channel filter bank covers a 20–20 kHz band, while the Q-factor of each channel can be tuned from 2 to 40. The simulation-predicted sensitivities of Q and ω0 to process/voltage/temperature (PVT) variations are less than 1%. The input-referred noise is no greater than 22 µVRMS, and the dynamic range is at least 68 dB for all filters in the bank.