In this paper, a new technique for improvement on the DC voltage gain, while keeping the high-linearity in symmetrical operational transconductance amplifier (OTA) bulk-driven (BD) topology is proposed. These features are achieved by allying two topological solutions: enhanced forward-body-biasing self-cascode current mirror, and source degeneration. The proposed concept is demonstrated through simulations with typical process parameters and Monte Carlo analysis on nominal transistors of the CMOS TSMC 180 nm node. Results indicate that the proposed OTA can achieve a very small transconductance, only 542 pA/V while keeping a voltage gain higher than 60 dB, 150 dB CMRR, and high linearity of 475 mVpp (1% THD), consuming only 1.9 nW for a supply voltage of 0.6 V. This set of features allows the proposed OTA to be an attractive solution for implementing OTA-C filters for the analog front-ends in wearable devices and bio-sensing.
This paper presents a novel differential pA/V Operational Transconductance Amplifier (OTA) topology. The circuit is suitable for the implementation of fully integrated operational transconductance amplifier-capacitance (OTA-C) filters with small feature size capacitors, suited for electrophysiological signal acquisition and conditioning. Unlike typical OTA-Cs, the proposed topology consists of transconductance reduction technique based on unbalanced output branches thatallow current subtraction thus enabling transconductances in the order of pA/V. The technique is demonstrated through the design of a 59pA/V transconductor, which is very suited for designing long-time-constant filters. This OTA-C achieved a worst-case 0.35% THD with just 61.7nW average power consumption, which allows its applicability to biomedical implants. Simulations were carried out with STMicroelectronics 0.13µm HCMOS9 node using Cadence’s IC design tools. Weemployed the OTA in a design of a fourth-order bandpass filter with a narrow bandwidth of 12.5–21.8Hz. Similar results to the ideal transfer function, turn the proposed OTA ideal for biosensing-based applications.
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