TDC1000: Some questions about ampfied signal connect to compin

Yes!

That drop(the earlier ringing) exists before amplified.

I guess it was a damping related to the impedance matching between rising RX signal through the ultrasonic sensor.

Could you give me your email address so that I can mail the sch to you?
Thanks a lot ~!!!

Thank you Bharat ~ I''ve got your mail. 

Hi , Bharat

I do not understand your question,the signal before going into PGAIN was only amplified by LNA gain(21dB). 

The PGA gain do work too , the signal from PGAOUT is larger than PGAIN ~

And I still can not resolve the problem ,previous oscillation occursed during the auto-zero time , that produce the early stop signals and made interference the time from START to STOP.

Here is the sch I designed :

And here is the simple external OP curcuit that I used for larger amplitude.

Hi , Bharat

I thought I had misunderstood your words.

Because the PGA gain inside TDC1000 is not big enough for me .

So I  use an external OP to amply the signal for increasing the voltage differential between each peak in the compin signal.

( in order to let Vthld not  too close to the peak , that produces wrong stop pulses )

And I had read another document (http://www.ti.com/lit/an/snaa284a/snaa284a.pdf) that says more detail funtion in TDC1000 ,

and found something may be the reasons that causing the ocsillation occurs in the "auto-zero time" observed on the COMPIN pin.

Except for this problem , I have another new questions and hope you can give me some suggestions .
Later , I will create a new forum. Thank you ~~~ !!