1. An apparatus for generating filtered return to zero multilevel data from binary non-return to zero (NRZ) data comprising: a binary finite impulse response (FIR) filter including a shift register means having a plurality of stages which receives the NRZ data, clock means for providing clock pulses to said shift register means for sampling each bit of NRZ data, a weighting element coupled to each stage for weighting each stage's output, and means for summing groups of said weighting elements to define summed signals, the number of weighting elements in each group not exceeding the number of clock pulses occurring during each bit of NRZ data; means for selectively inverting the polarity of each of said summed signals, said inverting means comprising an operational amplifier for each of said summed signals, and means for selectively biasing each operational amplifier to function either as an inverting amplifier or a noninverting amplifier; means responsive to each NRZ data bit for controlling the polarity selection of said inverting means in accordance with said return to zero multilevel data to be generated; and means for summing each of said polarity selected summed signals to define said filtered return to zero multilevel data.