current mode transmitter the arrangement is similar to the use of tomlinson precoding in a narrowband modem tomlinson m u201c new automatic equalizer employing modulo arithmetic u201d electronic letters march 1971 in a high speed digital system it is much simpler to equalize at the transmitter than at the receiver as is more commonly done in communication systems equalizing at the transmitter allows us to use a simple receiver that just samples a binary value at 4 ghz equalizing at the receiver would require an a d of at least a few bits resolution or a high speed analog delay line both difficult circuit design problems a discrete time fir equalizer is preferable to a continuous time passive or active filter as it is more easily realized in a standard cmos process after much experimentation we have selected a five tap fir filter that operates at the bit rate the weights are trained to match the filter to the frequency response of the line as described below for a 1 m 30 awg line the impulse response is shown in fig5 a each vertical line delimits a time interval of one bit cell or 250 ps the filter has a high pass response as shown in fig5 b as shown in fig6 a c this filter cancels the low pass attenuation of the line giving a fairly flat response over the frequency band of interest the decade from 200 mhz.