A continuous-time delta-sigma ADC for portable ultrasound scanners

Abstract

A fully differential fourth-order 1-bit continuous-time delta-sigma ADC designed in a 65 nm process for portable ultrasound scanners is presented in this paper. The circuit design, implementation and measurements on the fabricated die are shown. The loop filter consists of RC-integrators, programmable capacitor arrays, resistors and voltage feedback DACs. The quantizer contains a pulse generator, a high-speed clocked comparator and a pull-down clocked latch to ensure constant delay in the feedback loop. Using this implementation, a small and low-power solution required for portable ultrasound scanner applications is achieved. The converter has a supply voltage of 1.2 V, a bandwidth of 10 MHz and an oversampling ratio of 16 leading to an operating frequency of 320 MHz. The design occupies a die area of $$0.0175\hbox { mm}^2$$ . Simulations with extracted parasitics show a SNR of 45.2 dB and a current consumption of $$489 \,\upmu \hbox {A}$$ . However, by adding a model of the measurement setup used, the performance degrades to 42.1 dB. The measured SNR and current consumption are 41.6 dB and $$495\,\upmu \hbox {A}$$ , which closely fit with the expected simulations. Several dies have been measured, and an estimation of the die spread distribution is given.