Comparative study of low voltage OTA designs

The increased demand for Low Power/Low Voltage (LP/LV) circuits while maintaining high bandwidth and dynamic range, has led to widespread use of current-mode techniques in the design of analog circuits. Current trends in continual scaling down of transistor gate lengths and reduction in supply voltage have further added to the design challenges. This paper deals with the design of building blocks for current-mode circuit design, namely, Operational Transconductance Amplifier (OTA). Designs of three OTAs have been discussed. These OTAs operate at supply voltages about 3.3 V. Simulations have been carried out in Cadence (with Hspice) for Taiwan Semiconductor Manufacturing Corporation´s (TSMC´s) 0.35 μm CMOS process. The main aim of this paper is to present and compare new OTA designs, which have potential for use in LV applications. One of the proposed OTAs has further been fabricated and tested for real-time application. The application addressed is that of designing spectral shaping filters for use in Second Generation High-bit-rate Digital Subscriber Line Technology (HDSL-2). The relative performance of all the three OTAs has also been presented.