13. The detector of claim 11 further comprising voltage switching means for supplying the amplifier stage with a voltage from a second voltage rail, the voltage to the amplifier stage being reduced when there is no signal and being increased to the second rail potential after a signal is present.
11. The detector of claim 10 further comprising: an amplifier stage comprising a p-channel FET and an n-channel FET connected as an inverter amplifier with common gates connected to the second capacitor, and common drains connected to an output lead such that when the voltage on the second capacitor changes sufficiently from its quiescent value, the output lead is switched in polarity.