Piezo receiver - help desperately needed!

[gvanto]

piezo, receiver, circuit

I am trying to design a doppler shift detector (for blood velocity in animals) using an 8MHz piezo transmitter-receiver system.

The transmitter seems to be fine, I have a 2 Volt p-p squarish wave across our 5nF driver-piezo.

I have followed Horrowitz and Hill closely in trying to come up with a receiver end but with no luck. I have tried everything from source-followers (as high-impedance input) followed by common-emitter amplifier stages, to emitter-followers (lower output impedance) to cascodes to combinations of these! The output still has: 1) Low gain (about 20, after 2 stages of C-E amplification) 2) Very distorted waveform from that which is being transmitted.

Our oscilloscope has a input impedance of 1MOhm parrallel with 20 pF, which at 8MHz is quite low and loading the circuit.

Also, almost every circuit diagram we have come across in texts, on the net, etc uses a coupling-transformer from the receiver-piezo - is this a must?

Please any help would be greatly appreciated,
Regards
Gert

 

[frannk]

can you supply the schematics to what you've done? maybe more of us can help you better that way. a piezo reciever is not something we come accross very often.

 

[Cluricaun]

Hi

You can search the forum, other doppler questions and similar hardware have been discussed there.
Perhaps you already seen it but here is a similar for bloodflow.

/Cl

 

[Mike zhang]

you can look at this paper.