Ultra low-FOM high-precision ΔΣ modulators with fully-clocked SO and zero static power quantizers
In this paper, two high-precision switched-opamp (SO) based ΔΣ modulators with ultra low figure-of-merit (FOM) are introduced respectively for bio-medical and audio applications. To save 50% power, both modulators adopt novel fully-clocked current mirror SOs with new bias circuits especially designed for SO. Besides, several measures are proposed separately in two modulators to ensure high performances. Both circuitries are implemented in 0.18µm CMOS. The modulator-I, for bio-medical applications, employs high density MOSCAPs to reduce chip area. Also, an innovative zero static power quantizer using MOSCAP-strings is developed to save up to 96% power and 69% area than traditional structure. With only 13µW power consumption at 1.0V supply voltage, it achieves 85dB peak-SNDR, 44.7fJ/conv.-step FOM for 10 kHz bandwidth. In the modulator-II, for audio applications, a novel 17-level scheme consisting of only nine comparators and two capacitor-strings is introduced to remove static power completely and save 40% chip area over the traditional quantizer. In addition, a dual cycle shift (DCS) DWA technique is introduced here to suppress in-band tone effectively. The modulator-II achieves 92dB peak-SNDR and 35.6fJ/conv.-step FOM with only 58µW power consumption at 0.9V supply voltage.