Thanks for the help everybody. The reduction of the sine wave is not a problem anymore. I now have signals between +/-4 instead. My goal now is to:

Take the signal and clip above +/-1V with (zener) diodes, add a DC component of 1.65V and amplify the remaining signal to fit in the window 0-3.3V. The idea is that I'm interested in the segment +/-1V of the +/-4V signal, which I want to sample in my analyzer that only takes 0-3.3V.

I have attached my Pspice model of my preliminary circuit, what do you think? As you might have guessed, this is not my area of expertise so please tell me if I'm missing something in this circuit or if you have better ideas.

Also, when I simulate this circuit I get distortions. I believe this has to do with the high frequency of my signal and the lack of proper components in my student version of Orcad.

Thanks again for you help guys!

 

Thanks for the help everybody. The reduction of the sine wave is not a problem anymore. I now have signals between +/-4 instead. My goal now is to:

Take the signal and clip above +/-1V with (zener) diodes, add a DC component of 1.65V and amplify the remaining signal to fit in the window 0-3.3V. The idea is that I'm interested in the segment +/-1V of the +/-4V signal, which I want to sample in my analyzer that only takes 0-3.3V.

I have attached my Pspice model of my preliminary circuit, what do you think? As you might have guessed, this is not my area of expertise so please tell me if I'm missing something in this circuit or if you have better ideas.

Also, when I simulate this circuit I get distortions. I believe this has to do with the high frequency of my signal and the lack of proper components in my student version of Orcad.

Thanks again for you help guys!

I was going to tell you earlier that you could clip the signal, but you were adamant about maintaining the sine wave. Some people learn the hard way.
You are using 4.7V zeners to clip the signal. 1V zeners don't exist. There are other ways to clip at ±1V, which we can discuss.
Your input is 50 Hz. You said the signal was 5 MHz. What's that all about?
The amplifier has slightly greater than unity gain at DC, but very little gain at 5 MHz, due to the fact that LM324 is a crappy op amp.
If you clip at ±1V, you have very little room for gain before you start overdriving the A/D. Do you have any idea how much gain you need?
What is the source impedance of your signal? Is it coming straight from the transducer? If so, you may need a preamp in front of the clipper.

 

Hi again,

First, look at figure 6 on www.rehab.research.va.gov/jour/00/37/4/wang.htm. In the image you can see the transmitted signal (higher amplitude) and echoes (smaller amplitude). When I clip the signal I don't care about the "morphology" of the transmitted signal, but it is important that my echoes doesn't get distorted. In my case the transmitted signal is +/-4V while the echo is +/-1V, hence I wanted to clip down to +/-1 so that the whole echo signal is preserved.

Second, in the circuit I used 50Hz just to try to see what happened at lower frequencies. That is, I forgot to change it before I took the picture. So, 5MHz is the frequency in question. Sorry for the confusion.

I want to use the whole 0-3.3V range that the ADC can handle, hence I want my +/- 1V signal to range between 0-3.3 hence I need a gain of about 1.65 (giving me a signal of +/- 1.65) and then move up the DC to 1.65. Which I hope will give me a signal of the range 0-3.3 where my echo has values in the whole range giving me good resolution. And of course also with preserved shape.

Could you recommend OPs and diodes that can work properly at this frequency?

 

... The transducer is connected via a pulser/receiver which has the out impedance of 50ohm.

In this youtube clip they use the same type of pulser https://www.youtube.com/watch?v=jsBEc6QS-yQ

Thanks for the help Ron.

 

Does the transducer put out a sustained burst of constant amplitude (sound pressure) 5 Mhz sine wave, or is it an impulse with damped ringing, or ???
If it is a burst, what is the duration?
I need to have some idea of the transmit waveform. The reflection is what it is, of course.

 

It is an impulse with a damped ringing. See attached image. You can see both the transmitted signal and the echo.

 

Do you have control of when the transmission occurs, or is it coming from a unit which is autonomous (out of your control)? If you were generating it, you could simply gate it out, giving you a lot more room for gain on the echo signal.

 

I trigger the pulser via my DSP in a autonomous way and I also need the location of it to be able to calculate the difference between them.

But if we go back to the clipping part, you said there are different ways to do this. Which are the different ways?