Chandu,
If you are setting the bias current to zero to isolate the afe during transmit pulse you need to be aware that when you turn the bias current on it will inject a bump into the signal that will transmit to your transducer corrupting your transmit pulse. For this reason we are looking at leaving the TX810 bias on throughout the transmit/receive time period. I have used all the same parts as you except a different pulser IC.
Regards.