A high-accuracy cascade sigma-delta A/D-converter

A high-accuracy cascade sigma-delta A/D-converter is presented. This A/D-converter consists of a 4th-order sigma-delta modulator with 2–2 cascade topology(two stages, both are 2nd-order modulators), a 5th order digital decimation filter, the bias circuit and the clock circuit. The 4th-order sigma-delta modulator is designed using a novel transfer function, that enables the modulator to process the signal ranging from supply tail to ground without losing linear performance. It also keeps each integrator's output half of the full amplitude, showing a positive contribution for linearity. The chip of this converter is realized by 0.35 um standard mixed signal technology and the die area is 9mm². At 2MHz sampling rate and 64 oversampling ratio, the measured signal-to-noise ratio for the overall circuit is 107dB.