2 CWD Block Diagram and Designs

Figure 2-1 shows a typical CWD receive system. Four main components exist in the CWD receive signal chain. the four components include ultrasound receive AFEs, summing network, amplify and filtering and the sampling ADC. The summing network sums all the I and Q signals from the I and Q output channels respectively, then produces differential I and Q signals for analysis. The maximum signal frequency of I and Q signal can be in the range of 10kHz to 100kHz. The ADC used to digitize these signals can have sampling speed at least 10 times higher than the maximum input frequency. Besides, high-resolution of 16-bits or more is needed for precise measurement of blood speed. For better signal conditioning of input, a fully differential amplifier (FDA) is usually used to drive the ADC. High-speed and low-noise performance must be taken into consideration while selecting ADC driver amplifier. For more information on how to drive a SAR ADC, refer to TI ADC Precision Labs

Based on Figure 2-1, TI is currently providing four proposals.