Mariusz,
thanks for answering the quesitons! i agree with you that TGC frequency is not a common term. Our AFE5808/9 datasheets use pulse repetition frequency (PRF) since it is a more common term in ultrasound industry.
Just i would like to comment on the 2.6ms number in the previous post. it should be 260us for 20cm depth. ms is very uncommon in medical applications. for big animal imaging systems or sonar systems, ms TGC control can exist.
in our AFE5808A/9 datasheets, we recommended the following. it may be helpful for the VCntl circuit design.
Thanks!
Typical VCNTLM,P signals are generated by an 8bit to 12bit 10MSPS digital to analog converter (DAC) and a
differential operation amplifier. TI’s DACs, such as TLV5626 and DAC7821/11 (10MSPS/12bit), could be used to
generate TGC control waveforms. Differential amplifiers with output common mode voltage control (that is,
THS4130 and OPA1632) can connect the DAC to the VCNTLM/P pins. The buffer amplifier can also be configured
as an active filter to suppress low frequency noise. The VCNTLM/P circuit shall achieve low noise in order to
prevent the VCNTLM/P noise being modulated to RF signals. It is recommended that VCNTLM/P noise is below 25nV/rtHz at 1KHz and 5 nV/rtHz at 50 KHz. More information can be found in the literatures SLOS318F and
SBAA150. The VCNTL vs Gain curves can be found in Figure 3. The below table also shows the absolute gain vs.
VCNTL, which may help program DAC correspondingly.