Automated Design Technique for Constant-gm Rail-to-Rail for OTA Input Stage

This paper presents a novel technique for an automated design to produce a constant transconductance (g(m)). This constant g(m) is valide over the entire common-mode input range for input stage of Low Voltage (LV) operational transconductance amplifier (OTA) based on DC level shifter. The issue lies at the input sage so, this automated design technique is created to rail-to-rail input stage of OTA. The key parameter is the bias current in DC level shifter (Ish). The proposed technique is responsible for finding the optimal Ish to obtain minimum variation on the g(m) of the OTA input stage. This technique is based on a script written on Linux, operating system, to be connected to the BSIM MOST model and netlist of the desired topology. Utility of the physics-based g(m)/I-D characteristics, this technique is more suitable for short channel transistors in sub-micron processes. This work allows the design problem to be cast as a program. So, it offers an efficient, reliable, and fast way to implement high-performance of analog integrated circuits. The results demonstrate that g(m) variation can be restricted within +/- 1.25 %. The circuit is simulated in IBM 0.13 mu CMOS technology with a single power supply 1.5-V.