JAJSI43C December 2015 – October 2019 DS250DF810
PRODUCTION DATA.
The DS250DF810 output driver has a three-tap finite impulse response (FIR) filter which allows for pre- and post-cursor equalization to compensate for a wide variety of output channel media. The filter consists of a weighted sum of three consecutive retimed bits as shown in the following diagram. C[0] can take on values in the range [-31, +31]. C[-1] and C[+1] can take on values in the range [-15, 15].
When utilizing the FIR filter, it is important to abide by the following general rules:
The FIR filter is used to pre-distort the transmitted waveform in order to compensate for frequency-dependant loss in the output channel. The most common way of pre-distorting the signal is to accentuate the transitions and de-emphasize the non-transitions. The bit before a transition is accentuated via the pre-cursor tap, and the bit after the transition is accentuated via the post-cursor tap. The figures below give a conceptual illustration of how the FIR filter affects the output waveform. The following characteristics can be derived from the example waveforms.