A Very Low Power Delta Sigma Modulator Using Optimized Bulk Driven Telescopic OTA for Biomedical Devices

Abstract

This paper presented a very low power 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order feedforward (FF) delta sigma (ΔΣ) modulator implemented with switched capacitors (SC) integrators. These integrators are based on a telescopic operational transconductance amplifier (OTA) which used the bulk-driven technique, optimized via the particular swarm optimization (PSO) algorithm. The ΔΣ modulator was designed for ultra-low power implantable medical devices such as the ECG measurement tool. The proposed Bulk Driven fully differential telescopic OTA with very low threshold voltages was considered under ±0.5V supply voltage. The bulk-driven OTA was optimized through the PSO algorithm resulting in high performances. In fact, the OTA simulation results showed a DC gain of 64dB, a GBW of 575 kHz, a phase margin (PM) of 80.8 degrees and an input-referred noise of 1.3f.μ/√Hz for a low bias current of 0.075μA. The bulk driven telescopic OTA was implemented using TSMC 0.18μm CMOS technology and it consumed only 0.19μW. The designed FF ΔΣ modulator reached a peak SNR of 53dB and an ENOB of 8.54 bits while the total power consumption was only 0.386μW over a 250Hz signal bandwidth and a 25 kHz sampling frequency (Fs).