hevans1944
Hop - AC8NS
If you look at the forward voltage versus forward current transfer function of a silicon, or germanium or Schottky diode you will see that both the forward voltage and the forward current go through zero simultaneously, and that the forward voltage drop is a function of the current through the diode and its composition. This means that for very small currents, the diode forward voltage drop is also small, approaching zero. Thus the full CMOS output voltage is available if the load on the diode is small enough. We use 0.6 or 0.7 V as the voltage drop across a silicon diode like the 1N914, but that is only valid at a particular current through the diode which occurs near the "knee" of the curve, where the forward bias reduces the depletion region of the diode junction to zero. The diode still behaves as a rectifier even for microvolt level signals, as witness the operation of any crystal radio receiver, but it does not always introduce the voltage drop that occurs at the knee of the I vs V transfer function.
