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A Sinusoidal Signal Generator Using a Constant Gain Finite Impulse Response (FIR) Filter for Electrical Bioimpedance Spectroscopy

We propose a sinusoidal signal generator (SSG) using a constant gain finite impulse response (FIR) filter for measuring impedance spectrum from 1-kHz to 2.048-MHz range. A simple digital-to-analog converter (DAC) using eight unit resistors generates differential stepwise signals and the FIR filter attenuates close-in harmonics of the stepwise signals using its inherent nulls. A continuous-time (CT) low-pass filter (LPF) attenuates high-order harmonics of the FIR filter's output. The fabricated SSG achieved the total harmonic distortion less than 0.2% up to 10th harmonic using a simple DAC and low oversampling ratio of 8. Since our SSG adopts a passive type of CT LPF and a constant gain FIR filter which does not require any gain compensation circuit, the fabricated SSG consumed 5.1 mW which is about 30% of our previous SSG.