Clock Rate and SSR Planning - 2023.2 English

Vitis Tutorials: AI Engine (XD100)

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2023.2 English

Channelizers today can operate at sampling rates between 10 and 20 GSPS. With typical AI Engine and PL clock rates of 1 GHz and 500 MHz respectively, this implies channelizers require Super Sample Rate (SSR) operation where several I/O samples are produced and consumed on clock every cycle. A feasible clocking strategy is based on the following:

  • IFFT processing employs sizes N = 2^m and hardware solutions become overly complex unless SSR = 2^n. Here SSR = 4, 8, or 16 makes sense given M = 16 for this design.

  • Hardware design is further simplified when the input sampling rate Fs contains a factor of Q=7 matching its output oversampling factor P/Q = 8/7 because the output sampling rate is then an integral number of clock cycles.

  • AI Engine supports clock rates ranging from Fc = 1.0 GHz to 1.3 GHz depending on speed grade. It follows SSR = Fs/Fc ranges from 10/1.3 to 20/1.0.

A suitable clocking strategy can be identified based on these considerations. This tutorial targets a nominal Fs = 10 GSPS with SSR = 8 for an AI Engine nominal clock rate of Fc = 1.25 GHz. This performance may be met with a “-2M” speed grade device, the specific clock rates chosen as appropriate to satisfy the Q=7 divisibility requirement.