Continuous-time analog filter with passband constant IIP3 based on common-gate amplifier

This paper presents an analog filter based on Rauch biquadratic cell. The filter exploits an improved analog stage that makes linearity performance uniform over the entire pass-band frequency region. All feedback analog filters suffer from poor linearity when the input tones frequency is in close proximity to the closed-loop poles frequency, where loop-gain reduces. This often forces an overdesign with higher current (higher power consumption) and/or higher overdrive voltages (lower dynamic range) in order to meet the linearity specifications over the whole filter pass-band region. The hereby proposed Rauch scheme resolves such a binding issue without power increasing and having the same IIP3 at low and at high frequency (up to the filter closed-loop poles frequency). Hence the linearity performance is in first approximation independent on the input tones bandwidth. In order to validate the hereby proposed idea a 4th-order 25 MHz −3 dB bandwidth pseudo-differential filter has been designed and simulated in CMOS 28 nm technology. The prototype consumes 820 µW from 1 V supply voltage and has 15 and 13 dBm IIP3 at 5 and 6 and 20 and 21 MHz input tones, respectively.