Design of low power, programmable low-Gm OTAs and Gm-C filters for biomedical applications

In this paper, two programmable operational transconductance amplifiers (POTAs)-one using bulk driven attenuator (BDA) and another using programmable current mirror (PCM) are proposed in order to achieve low-Gm and high dynamic range. These OTAs are denoted as BDA-POTA and PCM-OTA respectively and are realized using composite transistors operated in the subthreshold region. The pseudo resistor is used for achieving programmability in the former and for improving the linearity and dynamic range in the latter. The proposed OTAs and two 4th order programmable Butterworth low pass filters (LPF) are designed and implemented in CMOS 180 nm technology with a supply voltage of 0.9 V. Their performances are evaluated through post-layout simulations and are found to be superior compared to those of POTAs reported in the literature for biomedical applications. The power consumption, transconductance, dynamic range and input-referred noise of BDA-POTA and PCM-OTA are [25.2 nW, (7.89-15.61 nS), (77.54-74.89 dB), (39.86-51.19 mu V-rms)] and [72.81 nW, (5.49-174.5 nS), (91.20-84.39 dB), (17.19-34.92 mu V-rms)] respectively. The power dissipation and cut off frequency range of the LPF using BDA-POTA and PCM-OTA are [197.8 nW, (30-100 Hz)] and [209.8 nW, (16-971 Hz)] respectively. The latter achieves 13.6 times wider programmability with only 5% increase in power dissipation. The proposed LPFs have better FOM compared to those reported in the literature.