An adaptive equalizer finite impulse response (FIR) filter for high-speed communication channels with modest complexity, where the filter is iteratively updated during a training sequence by a circuit performing the update: h ( t + 1) = h ( t ) + µ [sgn { d ( t )} - sgn { z ( t ) - Kd ( t )}]sgn {x( t )} , where h ( t ) is the filter vector representing the filter taps of the FIR filter, x( t ) is the data vector representing present and past samples of the received data x ( t ), d ( t ) is the desired data used for training, z ( t ) is the output of the FIR filter, µ determines the memory or window size of the adaptation, and K is a scale factor taking into account practical limitations of the communication channel, receiver, and equalizer. Furthermore, a procedure and circuit structure is provided for calibrating the scale factor K.