System level design of a continuous-time ΔΣ modulator for portable ultrasound scanners

Abstract

Abstract-In this paper the system level design of a continuous-time ∆Σ modulator for portable ultrasound scanners is presented. The overall required signal-to-noise ratio (SNR) is derived to be 42 dB and the sampling frequency used is 320 MHz for an oversampling ratio of 16. In order to match these requirements, a fourth order, 1-bit modulator with optimal zero placing is used. An analysis shows that the thermal noise from the resistors and operational transconductance amplifier is not a limiting factor due to the low required SNR, leading to an inherently very low-power implementation. Furthermore, based on high-level VerilogA simulations, the performance of the ∆Σ modulator versus various block performance parameters is presented as trade-off curves. Based on these results, the block specifications are derived.

A 10 MHz bandwidth continuous-time delta-sigma modulator for portable ultrasound scanners

“…For the purpose of comparing the design with other converters, the commonly used figure of merit (FoM) of energy per conversion is used (1). Using the results of the simulated performance with parasitic extraction, the calculated FoM of the design is 197 fJ/conversion.…”

“…The layout of this block affects the unit delay of an inverter, therefore all the timing simulations need to be done with extracted parasitics. Following the specifications found in [1], the loop delay can not be higher than 300 ps. Simulations with extracted parastics including corners and mismatch variations show that the total loop delay vary from 210 ps to 298 ps with a nominal value of 252 ps.…”

“…In [1] the 64-channel system based on CMUTs was studied and the most adequate topology and specifications were derived. A fourth-order 1-bit CTDSM with optimal zero placing topology was chosen.…”

An Element-Matched Electromechanical <inline-formula> <tex-math notation="LaTeX">$\Delta\Sigma$ </tex-math> </inline-formula> ADC for Ultrasound Imaging

“…• The target SNR is 50dB. Note that the SNR of the final image will be higher than that, as the correlated outputs of multiple elements are combined, while the noise is uncorrelated [21]. System-level behavioral simulations suggested that the noise shaping introduced by the transducer is sufficient to reach the target SNR, provided that a 3-bit quantizer and a sampling frequency of 200MHz are used.…”