Design of Low Voltage Low Power High Gain Operational Transconductance Amplifier

Rajesh Durgam,S Tamil,Nikhil Raj

doi:10.24840/2183-6493_007.004_0008

Abstract

In this paper, a high gain structure of operational transconductance amplifier is presented. For low voltage operation with improved frequency response bulk driven quasi-floating gate MOSFET is used at the input. Further for achieving high gain the modified self cascode structure is used at the output. Compared to conventional self cascode the modified self cascode structure used provides higher transconductance which helps in significant boosting of gain of the amplifier. The modification is achieved by employing quasi-floating gate transistor which helps in scaling of the threshold which as a result increases the drain-to-source voltage of linear mode transistor thus changing it to saturation. This change of mode boosts the effective transconductance of self cascode MOSFET. The proposed operational transconductance amplifier when compared to its conventional showed improvement in DC gain by 30dB and also the unity gain bandwidth increases by 6 fold. The MOS models used for amplifier design are of 0.18µm CMOS technology at supply of 0.5V.

Highlights

The deep submicron device dimensions and low voltage operations have favoured the design of high performance circuits
The MOS transistor device dimensions taken for simulation purpose for CM operational transconductance amplifier (OTA) of Figure 3 are shown in Table 1 along with other assumed parameters for circuit simulations
As the OTA transconductance gets boosted it results in increased DC gainas well the unity gainfrequency

Summary

Introduction

The deep submicron device dimensions and low voltage operations have favoured the design of high performance circuits. Besides the advantage of SC MOSFET, it does suffer with a disadvantage in terms of requirement of large device dimensions Solutions in this context include using MOSFET of asymmetric threshold voltage (Vth) (Fujimori and Sugimoto 1998), MOSFET with dual-work function-gate (DWFG), zero threshold (ZVT) MOSFET (Na, Baek, and Kim 2012), body-biasing technique (Baek et al 2013) etc. Design of Low Voltage Low Power High Gain Operational Transconductance Amplifier Rajesh Durgam, S.Tamil, Nikhil Raj. Angulo et al 2004), and Bulk driven floating/quasi-floating Gate (BDFG/BDQFG) structure (Khateb 2014, 2015). Among the aforementioned techniques BD is chosen for very LV operation but it does suffer from low transconductance for which the BDQFG technique is preferred over it In these non-conventional techniques transconductance achieved is low compared to standard gate driven MOSFET which leads to low bandwidth circuits.

Self Cascode Structure

Simulation Results

Conclusion