Sun Dec 16 21:13:31 EST 2012

Exp converter

R/DD + R/C -> base voltage

R/DD network is a simple way to convert 3.3V to a range that makes
sense for base voltage: 0 - v_mid - 2x v_mid.

Transistor behaves as diode for this network, and 2 diodes in series
behave as one diode with different parameters.