Analog-to-digital converters (ADC) used in wireless applications need to digitize a small desired signal in the presence of large out-of-band interferers. This increases the dynamic range required of the ADC and hence results in significant power dissipation. To attenuate these interferers, it is common practice to place a continuous-time filter ahead of the ADC. However, the filter adds its own noise and distortion to the signal chain. Prior art shows that a CTΔΣM with an embedded Tow-Thomas filter achieves a better power efficiency, lower area, and higher linearity when compared to the same CTΔΣM with the filter placed up front. An alternative choice of filter topology, attractive since it uses only one opamp, is the Rauch structure. The Rauch filter has better out-of-band linearity compared to the Tow-Thomas. But its input noise spectral density is also higher. Prima facie, the appropriate choice of topology that should be used for the embedded filter in the CTΔΣM is not clear.

Another approach to realizing a filtering CTΔΣM is to embed a CTΔΣM into a low-pass filter. A question that immediately comes to mind is if this approach is preferable to embedding the filter into a CTΔΣM. This work investigates these threads and concludes that a CTΔΣM with an embedded Rauch filter is a compelling design choice. The theory is supported by measurement results from a filtering-CTΔΣM test chip that achieves a peak SNDR of 76.7dB in a 1MHz signal bandwidth. Measurements demonstrate improved power efficiency and out-of-band linearity when compared to prior art