A 1 MHz bandwidth, filtering continuous-time delta-sigma ADC with 36 dBFS out-of-band IIP3 and 76 dB SNDR

The high dynamic range of CTΔΣMs used in wireless receivers, needed to accommodate large out-of-band interferers, can be reduced by using a filter up front. Embedding the filter inside the modulator loop is more power efficient. Prior work has embedded a Tow-Thomas biquad inside the ADC. We show that using a Rauch filter instead yields higher out-of-band linearity (for the same power dissipation) due to the passive-RC filtering inherent in the Rauch structure. The theory is borne out by measurements from a 1 MHz bandwidth CTΔΣM with an embedded second-order Rauch filter, achieving 76 dB SNDR and 36 dBFS out-of-band IIP3 while consuming 2.2 mW in a 65 nm CMOS process¹.