A Near 1-V Operational, 0.18-µm CMOS Passive Sigma-Delta Modulator with 77 dB of Dyanamic Range

Toru SAI  Yasuhiro SUGIMOTO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E93-C   No.6   pp.747-754
Publication Date: 2010/06/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E93.C.747
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuits and Related SoC Integration Technologies)
Category: 
Keyword: 
passive sigma delta,  low voltage,  switched capacitor filter,  correlated double sampling,  

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Summary: 
A low-voltage operational capability near 1 V along with low noise and distortion characteristics have been realized in a passive sigma-delta modulator. To achieve low-voltage operation, the dc voltage in signal paths in the switched-capacitor-filter section was set to be 0.2 V so that sufficient gate-to-source voltages were obtained for metal-oxide-semiconductor (MOS) switches in signal paths without using a gate-voltage boosting technique. In addition, the input switch that connects the input signal from the outside to the inside of an integrated circuit chip was replaced by a passive resistor to eliminate a floating switch, and gain coefficients in the feedback and input paths were modified so that the bias voltage of the digital-to-analog converter could be set to VDD and 0 V to easily activate MOS switches. As the signal swing becomes small under low-voltage operational circumstances, correlated double sampling was used to suppress the offset voltage and the 1/f noise that appeared at the input of a comparator. The modulator was fabricated using a standard CMOS 0.18-µm process, and the measured results show that the modulator realized 77 dB of dynamic range for 40 kHz of signal bandwidth with a 40 MHz sampling rate while dissipating 2 mW from a 1.1 V supply voltage.