I need to deliver a 40 V (minimum), 4.25 MHz, sine wave to a PZT transducer (medical ultrasound application). I have explored trying to use a dc/dc step-up with a switch, but this will only give me a square wave as I understand it. Furthermore, I have tried to search oscillators but most give within the range of 1-3V outputs and as we all know, op-amps can't output more than their supply voltage an I'm trying to stay away from directly supplying 40V to a single element of my circuit. Any suggestions would be greatly appreciated as I feel I have hit a dead end.
Use 2 opamps, the first opamp is inverting, as is the 2nd opamp; first opamp has gain of -10, thus 1vpeak becomes -10 volts peak output; the 2nd opamp exactly (as exact you can get at 4.25MHz) inverts the first opamps -10v output to produce +10v peak. Now connect the piezo between the 2 opamp outputs.
Driving the first opamp with +-1v peak, will produce +- 10v peak from each opamp, and the complementary drive produces +-20 volts peak, or 40v peakpeak.
Now about an opamp to fairly accurately produce 10 volts at 4.25MHz: you will need a slewrate of 10v * 4.25 * 2 * PI === 240 volts/uS slewrate.
If that's for a single pulse, you can use off-the-shelf components. As a pulser, you could use:
- NMT0572SC for high voltage generation from 5V
- TC6320TG for pulse production (you still need to supply it with High Voltage), using a MD1213 for control
- Protect the rest of the design with a MD0100
And you have yourself a nice pulser board!