JAJSFC6C May 2015 – April 2018 ADS52J90
PRODUCTION DATA.
Typical requirements of a medical ultrasound receiver system are listed in Table 34.
DESIGN PARAMETER | EXAMPLE VALUES |
---|---|
Signal center frequency | 5 MHz-15 MHz |
Signal bandwidth | 2 MHz |
Maximum input signal amplitude | 100 mVPP |
Transducer noise level | 1 nV/√Hz |
Total harmonic distortion | 40 dBc |
The ultrasound system typically has an LNA and a time-dependent gain block at the front-end before the ADC. In an ultrasound receiver, the signal level keeps reducing as a function of time and the role of the front-end blocks is to gain up the signal level without adding too much additional noise. The gain of the front-end can be adjusted so that the input signal to the ADC always remains within its full-scale range.
A sampling rate of approximately 40 MHz to 50 MHz is usually sufficient for such an application. Thus the ADS52J90 can be operated in 16-input mode. Furthermore, the resolution can be set to 14 bits to maximize the SNR of the device. A higher sampling rate ADC results in a lower noise density in the signal band of interest. For example, an ADC with a 2-VPP input operating at 50 MSPS with an SNR of 73 dBFS has a noise level of approximately 35 nV/√Hz referred to the input of the ADC. If the front-end has a gain of 40 dB, the ADC noise referred to the input of the front-end is then 0.35 nV/√Hz, which in this case is lower than the transducer noise level.