Hi,
I am designing a preamplifier with a gain of 100x to amplify signals coming from ultrasonic piezoelectric transducers. The transducer generates differential signals in the 30 kHz–300 kHz range, with an amplitude of about 5 mVpp. I am not sure about the common-mode voltage amplitude. The main constraint of the design is power consumption + cost, since the device will be battery powered.
The transducer can be modeled as a series capacitance of 12nF and a series resistance of 10 ohms. In my LTSPICE simulation, I also included cables model to evaluate the CMRR performance when mismatch occurs.
The preliminary results look reasonable, but I still have some questions:
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how should I properly evaluate CMRR in the case of source mismatch (i.e different cables lenght or slightly different sensors)?
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Regarding the input bias resistors: how do I choose their value? The datasheet only reference the high-pass cutoff when using capacitive coupling at the input. In other designs, i see that high-value resistors (e.g. 1Mohm) are used.
Here's a screenshot of my simulation. I'm open to all kind of suggestions, including different p/n or topologies.
Thank you,
V
