Abstract

In ultrasound scanners, there is only one set of transducers, which is used for transmit as well as receive function (one after the other, using T/R switch). This supports scanning of stationary objects inside body for example, tissues, and bones. The blood is not stationary so continuous or simultaneous transmit and receive functions are a must. For this, the same transducer is split in half and used as simultaneous transmit and receive. Continuous Wave (CW) Doppler is a mode of capturing the echo when transmit and receive functions are happening simultaneously. Based on Doppler effect, the velocity of the blood and other parameters can be calculated. The CW Doppler is a key function in mid-end to high-end ultrasound systems and the CS Doppler must handle high dynamic range along with strict phase noise performance. This application note highlights key challenges of CW Doppler path and proposes four designs to achieve low-noise performance.