As shown in Figure 2-2, Proposal 1 adopts the THS4552 and ADS9224 as the CWD signal chain. The ADS9224 is TI's 16-bits ADC with internal reference and 3MSPS sample rate introduced in 2019. Because the CWD signal is divided into the In-phase signal and the Quadrature signal. this requires two amplifiers and two sampling ADCs, Regarding the ADS9224 and THS4552 both having dual channels. single ADS9224 and THS4552 can meet the CWD signal chain requirements, this proposal can be applicable for small size, cost-sensitive equipment such as hand-held or portable ultrasound with low dynamic range requirements. one benefits of this design is customer potential to implement an over-sampling to get better resolutions than 16-bits with low cost.

Figure 2-2 Proposal 1 ADS9224 and THS4552

Noise is one tough issue for electrical engineer. For CWD system, the situation is even worse since the reflect signals potential is very weak in a CWD system. Generally, the designer needs to evaluate the noise performance of circuit for CWD application. Figure 2-3 shows the circuit was simulated for evaluate noise performance of Proposal 1. In actual circuit design, there has several input signals with series resistor for add CWD signals from different AFEs. In the simulation, we use an equal resistor to replace these resistors. Figure 2-4 shows the frequency response and noise performance of Proposal 1 by simulation.

Figure 2-3 Proposal 1 Simulated Circuit

Proposal 1 noise and amplitude frequency characteristics.

Figure 2-4 Proposal 1 AC and Noise Performance

From the simulation result of Proposal 1, the total integrated noise within 1MHZ bandwidth is about 8.207uV.