A 900 mV 40 /spl mu/W switched opamp /spl Delta//spl Sigma/ modulator with 77 dB dynamic range
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Portable electronic systems require low-voltage low-power building blocks. An important building block is an A/D converter. /spl Delta//spl Sigma/ ADCs provide an efficient way of trading off speed for resolution. The switched op amp (SO) technique allows design of switched-capacitor (SC) circuits at very low supply voltage without the use of multithreshold technologies or voltage multipliers to drive the switches. The basic idea of it is to leave out the switches connected to the output of the amplifier in a SC integrator, because those are the ones that fail to conduct when the supply voltage is low. Switches can only be connected to well-chosen reference voltages. In this implementation the differential modified SO integrator cell is used, so the reference voltages are V/sub SS/ and V/sub DD/. This allows maximum overdrive of V/sub DD/-V/sub SS/ for the switches.
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