Upper and lower bounds for some depth-3 circuit classes

We investigate the complexity of depth-3 threshold circuits with majority gates at the output, possibly negated AND gates at level two, and MOD/sub m/ gates at level one. We show that the fan-in of the AND gates can be reduced to O(log n) in the case where m is unbounded, and to a constant in the case where m is constant. We then use these upper bounds to derive exponential lower bounds for this class of circuits. In the unbounded m case, this yields a new proof of a lower bound of Grolmusz; in the constant m case, our result sharpens his lower bound. In addition, we prove an exponential lower bound if OR gates are also permitted on level two and m is a constant prime power.