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

In this paper the system level design of a continuous-time ΔΣ 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 320MHz 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 ΔΣ modulator versus various block performance parameters is presented as trade-off curves. Based on these results, the block specifications are derived.