Lookup Table Vs. FIR For Modulator Pulse Shaping
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From: Steve Pope on 1 Apr 2010 18:32 cfelton <cfelton(a)n_o_s_p_a_m.ieee.org> wrote: >Is there any math / theorems that describe the behavior of a FIR filter as >a state-machine (trellis?). Could there exist a direct relation between, >say the state variable (2**(K*N)), and the output? I'm not sure if there are any theorems surrounding it, but what you are describing sounds like the concept behind a Forney equalizer. Steve
From: glen herrmannsfeldt on 1 Apr 2010 18:49 Steve Pope <spope33(a)speedymail.org> wrote: > glen herrmannsfeldt <gah(a)ugcs.caltech.edu> wrote: >>It is usual for FPGAs to have flip-flops at the output of each >>LUT, which makes systolic array pipelines real easy to build. >>If you latch at each logic level, they are really fast, too! > Doesn't the usual definition of "systolic array" require that > there is no globally synchrnous clock, that instead the clock > follows the data around? All the ones I know have a global clock. > And if so, would one really design with an FPGA in such a fashion? Systolic array is more an architecture than an implementation. One could clock them differently, and in some cases I think it is useful. For example, in a multi-board array having a separate clock for each board, syncronized with the data, seems like it might work better than a global (multi-board) clock. -- glen
From: Steve Pope on 1 Apr 2010 19:03 glen herrmannsfeldt <gah(a)ugcs.caltech.edu> wrote: >Steve Pope <spope33(a)speedymail.org> wrote: >> Doesn't the usual definition of "systolic array" require that >> there is no globally synchrnous clock, that instead the clock >> follows the data around? >All the ones I know have a global clock. >> And if so, would one really design with an FPGA in such a fashion? >Systolic array is more an architecture than an implementation. >One could clock them differently, and in some cases I think it >is useful. For example, in a multi-board array having a separate >clock for each board, syncronized with the data, seems like it >might work better than a global (multi-board) clock. We did a Reed-Solomon decoder with such a clocking approach once. It is written up in the chapter by Berlekamp et. al. in Stephen Wicker's book _Reed Solomon Codes_ . It was necessary because we used ECL logic and it was attractive to not have to run an entire large board synchrnously. However, each FPGA was itself synchronous. Steve
From: glen herrmannsfeldt on 1 Apr 2010 20:17 Steve Pope <spope33(a)speedymail.org> wrote: (snip regarding systolic arrays and global clocks) > We did a Reed-Solomon decoder with such a clocking approach once. > It is written up in the chapter by Berlekamp et. al. in Stephen Wicker's > book _Reed Solomon Codes_ . > It was necessary because we used ECL logic and it was attractive to > not have to run an entire large board synchrnously. However, each > FPGA was itself synchronous. The ones I know have data going only one direction, which allows for various different clock methods. Among others, you can latch all the signals at any point and delay them. There are systolic arrays with data going both directions, though. Also 2D arrays, with data flow in orthogonal directions. For systolic array search processors the array length determines the allowed query length. I have known virtual arrays that run the data through and store all the array output, then load the next part of the query and run the data through that, again storing the array output. -- glen
From: Jerry Avins on 1 Apr 2010 23:54
On 4/1/2010 8:17 PM, glen herrmannsfeldt wrote: > Steve Pope<spope33(a)speedymail.org> wrote: > (snip regarding systolic arrays and global clocks) > >> We did a Reed-Solomon decoder with such a clocking approach once. >> It is written up in the chapter by Berlekamp et. al. in Stephen Wicker's >> book _Reed Solomon Codes_ . > >> It was necessary because we used ECL logic and it was attractive to >> not have to run an entire large board synchrnously. However, each >> FPGA was itself synchronous. > > The ones I know have data going only one direction, which allows > for various different clock methods. Among others, you can latch > all the signals at any point and delay them. There are systolic > arrays with data going both directions, though. Also 2D arrays, > with data flow in orthogonal directions. > > For systolic array search processors the array length determines > the allowed query length. I have known virtual arrays that run > the data through and store all the array output, then load the > next part of the query and run the data through that, again storing > the array output. Asynchronous operation is commom in hardware FIFOs. I may have built the first with discrete IC logic, and I recall a few LSI designs. Chuck Moore of Forth fame builds CPUs that way. Jerry -- "It does me no injury for my neighbor to say there are 20 gods, or no God. It neither picks my pocket nor breaks my leg." Thomas Jefferson to the Virginia House of Delegates in 1776. ��������������������������������������������������������������������� |