A 1 V 59 fJ/Step 15 MHz BW 74 dB SNDR continuous-time ΔΣ modulator with digital ELD compensation and multi-bit FIR feedback

Abstract

A 3rd-order continuous-time ΔΣ modulator with a highly-digital excess loop delay compensation and multi-bit FIR feedback, to be used in an ultrasound beamformer, is presented. A digitally controlled reference switching matrix avoids the power-hungry adder, and allows a power-efficient design of the loop filter. A 2-bit 3-tap FIR feedback DAC optimally achieves lower sensitivity to clock jitter and applies reduced error signal to the loop filter, thus enhancing the loop filter linearity. The modulator operates at 1.2 GHz, and achieves 79.4 dB dynamic range, 77.3 dB SNR and 74.3 dB SNDR over a 15 MHz signal bandwidth. Fabricated in a 65 nm CMOS process, the core modulator occupies 0.16 mm2 and dissipates 6.96mW from a 1 V supply. A 58.6 fJ/conversion-step figure of merit is achieved.