What is claimed is:
1. A nonlinear circuit for calculating activation function derivatives on stochastically encoded signals, said circuit comprising
- an OR gate for receiving at least first and second inputs representative of first (A) and second (B) stochastically encoded signals each having a spike frequency coding over a given interval, said first gate forming as an output the logical OR function f(A+B),
- a delay gate for receiving said f(A+B) function to form an inverted and delayed output 1-f(A+B),
- an AND gate for receiving said f(A+B) and 1-f(A+B) signals to form the approximate derivative quantity output signal f(1-f).
2. The circuit as in claim 1 wherein said delay gate delays one of said f(A+B) signals by at least one clock cycle so as to decorrelate said signals.
3. In a circuit for calculating activation function. derivatives on stochastically encoded signals, the method comprising the steps of
- receiving at least first and second inputs representative of first (A) and second (B) stochastically encoded signals each having a spike frequency coding over a given interval to form as an output the logical OR function f(A+B),
- receiving said f(A+B) function to form an inverted and delayed output 1-f(A+B), and
- receiving said f(A+B) and 1-f(A+B) signals to form the approximate derivative quantity output signal f(1-f).
