Sub-µW Switched-Capacitor Circuits Using a Class-C Inverter

Minho KWON  Youngcheol CHAE  Gunhee HAN  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E88-A   No.5   pp.1313-1319
Publication Date: 2005/05/01
Online ISSN: 
DOI: 10.1093/ietfec/e88-a.5.1313
Print ISSN: 0916-8508
Type of Manuscript: PAPER
Category: Analog Signal Processing
Keyword: 
class-C inverter,  low-power,  low-voltage,  switched-capacitor circuits,  

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Summary: 
In a switched-capacitor (SC) circuit, the major block is an operational transconductance amplifier (OTA) designed in order to form a feedback loop. However, the OTA is the block that consumes most of the power in SC circuits. This paper proposes the use of a class-C inverter instead of the OTA in SC circuits and a corresponding switches configuration for extremely low power applications. A detailed analysis and design trade-offs are also provided. Simulation and experimental results show that sufficient performance can be obtained even though a class-C inverter is used. The second-order biquad filter and the second-order SC sigma-delta (ΣΔ) modulator based on a class-C inverter are designed. These circuits have been fabricated with a 0.35-µm CMOS process. The measurement results of the fabricated SC biquad filter show a 59-dB signal-to-noise-plus-distortion ratio (SNDR) for a 0.2-Vp-p input signal and 0.9-V dynamic ranges. The power consumption of the biquad filter is only 0.4 µW with a 1-V power supply. The measurement results of the fabricated ΣΔ modulator show a 61-dB peak SNR for a 1.6-kHz bandwidth with a sample rate of 200 kHz. The modulator consumes 0.8 µW with a 1-V power supply.