A 4 Bit Continuous-Time <inline-formula> <tex-math notation="LaTeX">$\Sigma \Delta $ </tex-math> </inline-formula> Modulator With Fully Digital Quantization Noise Reduction Algorithm Employing a 7 Bit Quantizer

Abstract

This paper presents a fully digital quantization noise reduction algorithm (DQNRA) for $\mathrm {CT}\Sigma \Delta \mathrm {M}$ . The algorithm overcomes the signal leakage issues commonly found in cascade and MASH implementations. The proposed DQNRA is robust to PVT variations. The DQNRA performs a foreground measurement of the modulators noise transfer function. A $\Sigma \Delta \mathrm {M}$ using a 7 bit quantizer, from which the four most significant bits are used for the operation of the $\Sigma \Delta \mathrm {M}$ , proves the DQNRA concept. The remaining three least significant bits are used for the realization of the DQNRA for quantization noise improvement. A 7 bit quantizer with a three-step subranging architecture is implemented to reduce power and area consumption. A fourth-order continuous-time $\Sigma \Delta $ prototype was implemented in 130 nm CMOS technology. The modulator’s total power consumption is 20 mW, with only 6 mW used for the realization of the 7 bit quantizer operating at 500 MHz. For this prototype, the use of a DQNRA algorithm improved the modulator’s SNDR from 69 to 75 dB over a 15 MHz bandwidth, limited after calibration by thermal noise rather than quantization noise. The obtained FoM is 164 dB.