A SELF BIASED OPERATIONAL AMPLIFIER AT ULTRA LOW POWER SUPPLY VOLTAGE 1B.E.(Hons.)

Sai Praneeth G A V1, Anil Kumar Saini2 Electrical and Electronics Engineering, Birla Institute of Technology and Science (BITS) – Pilani, India 2VLSI Design Centre, Central Electronics Engineering Research Institute (CEERI) – Pilani, India

Abstract

3. Advantages

This paper discusses the design of a self-biased folded cascode Op-Amp at 0.5V. The proposed design is first of its kind at 0.5 V where self-biasing techniques are used to reduce power and area overheads. The self-biasing scheme is developed by using a current mirror for low voltage operation. This design is implemented in a 90 nm CMOS technology using Cadence GPDK.

1. Introduction

Op-Amp is a main analog building block for modern wireless and biomedical applications. In this work, an op-amp is designed with a novel selfbiasing scheme which is a combination of standard low voltage and RajputJamuar current mirrors.

2. Circuit Design

A Low Voltage Self-Biased Op-Amp

1.  The feedback network complexity is reduced by eliminating a diode-like connection. 2.  The operational amplifier consumes low power. 3.  This design is also robust to temperature and process variations.

4. Results

The proposed design has the highest Power Supply Rejection Ratio - 67.3

Rajput-Jamuar Current Mirror

Vds1 is controlled by the equation Vds1=Vgs1-Vgs3. This current mirror is incorporated into the self biased folded cascode amplifier in order to operate it at 0.5V. Transistors M12 and M14 are stacked which eliminates the need of bias current sources for their operation.

Proposed Design

A reduction of power by 4 times when compared to an externally biased 2 stage OTA has been achieved

The proposed design has the highest Unity Gain Frequency with a load capacitor of 3pF.

The gain was found to be varying by a mere 1.1 dB/ 5 C

5. Conclusion

This paper discussed the design of a self-biased op-amp at 0.5 V in a 90 nm CMOS technology using a modified current mirror. A new selfbiasing scheme has been proposed which combines a standard low voltage cascode current mirror with Rajput-Jamuar current mirror. It has been shown that the proposed opamp consumes considerably low power and yet provides high bandwidth.

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