Re: square law detector
The current through a diode is given as:
I = Io (exp(q Vd/kT) - 1)
where Vd is the forward bias voltage drop on the diode. If the 1 is ignored (which can be done for even small Vd's at room temperature) and the exp term expanded in a series of powers of Vd, then the diode curve can be approximated reasonably by an expression consisting of terms upto the square of Vd. So this square law expression represents th diode current. Now when Vd is a modulated signal, this square term would produce the sum and difference of the carrier and the signal frequencies. The carrier can be filtered out giving the signal.
Thus since we use the square term explicitly to detect a signal, the diode is sometimes called the square law detector.