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New Liquid Crystal Panel AC driver for DOLPi

AC Driver for the DOLPi Polarization Camera by David Prutchi PhD

Although the circuit of shown so far as the liquid crystal panel’s AC driver works well, I’m not too happy with the intrinsic non-linearity of the FET.  Because of this, today I designed and tested an alternative, a bit more complex, but I believe more elegant design.  In the circuit shown above, the LCP drive amplitude tracks linearly with the DAC’s output.

The non-inverting amplifier built around U1 approximately doubles the output of the DAC. This voltage is then presented to an H-bridge implemented by the analog switches in U2. The H-bridge produces a continuous biphasic train at a frequency given by the oscillator built around U3A and U3B. U4 doubles the +5V coming from the Raspberry Pi to power U1 and U2. The LCP is connected between the legs of the H-bridge.

 
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