Design of Low Power Discrete Time FF ΔΣ Modulator for Biomedical Application

Abstract

High speed, low voltage delta-sigma (ΔΣ) analog to digital converter (ADC) is required for low power medical applications. A second order discrete time (DT) feed forward (FF) ΔΣ modulator with very low power consumption is presented in this paper. The OTA is the key building block and the most power-hungry circuit for ΔΣ modulator design. Using TSMC 0.18μm CMOS technology, the telescopic OTA is optimized using the practical swarm optimization (PSO) algorithm; it achieves a DC gain of 62dB, a GBW of 166.6MHz and it consumes only 35μW. The optimized FF ΔΣ modulator has been implemented with an OSR of 50, a signal bandwidth of 0.5MHz and a sampling frequency of 50MHz. The designed modulator is suitable for low medical application in 2.4GHz ISM band for IEEE 802.15.1/Bluetooth standard. This circuit attains a peak SNR of 52dB and a resolution of 8,34bits. This topology consumes only 71μW under 1.8V supply voltage.