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Electronics Forum / CAD / August 2008LTspice - fast NRZ pulses how?
Does anyone know a trick to make fast random NRZ pulses in LTspice? I don't want to use the read-from-file option, but would like to generate them procedurally. This is for speed and convenience. The pulses should be rectangular, be 1s (or whatever 1/datarate is) and be either +1 or -1, with a random probability distribution. You could probably use two independent sources to make a multiplicative congruental generator. Something like Va = fraction ( pi * Vb ) and Vb = Va. You'll have to set up Va to be nonzero when the simulation starts, and I'm not sure how you would put in a proper time delay between the two sources. Then you have a pseudorandom number, to make data, you'll probably have to sgn() it etc. Probably need a sample & hold to to hold it still for one bit period. On Aug 28, 7:55 pm, wavema...@sogetthis.com wrote: > Does anyone know a trick to make fast random NRZ pulses in LTspice? > [quoted text clipped - 5 lines] > The pulses should be rectangular, be 1s (or whatever 1/datarate is) > and be either +1 or -1, with a random probability distribution. Thanks! I tried this: * C:\Program Files\LTC\SwCADIII\nrz_sim\random_nrz_bits.asc B1 a 0 V = if ( rand( time ) , 1, -1 ) .tran 1000 .backanno .end and it seems to work! It's fast too - around 4000 seconds per second. How about some other tricks to accomplish the same? > You could probably use two independent sources to make a > multiplicative congruental generator. [quoted text clipped - 20 lines] > > The pulses should be rectangular, be 1s (or whatever 1/datarate is) > > and be either +1 or -1, with a random probability distribution. That's a cool trick. For grins, I tried B1 a 0 V= pi*v(a) - floor( pi*v(a) ) combined with a sample & hold. That worked too, but it's a lot slower. On Aug 29, 12:13 pm, wavema...@sogetthis.com wrote: > Thanks! I tried this: > [quoted text clipped - 33 lines] > > > The pulses should be rectangular, be 1s (or whatever 1/datarate is) > > > and be either +1 or -1, with a random probability distribution. > Does anyone know a trick to make fast random NRZ pulses in LTspice? > [quoted text clipped - 5 lines] > The pulses should be rectangular, be 1s (or whatever 1/datarate is) > and be either +1 or -1, with a random probability distribution. Hello, I recommend a B-source. V={ampl}*(rand(time*{br}) >=.5) .param br=533meg .param ampl=2 The option below enables the eye diagram. .options baudrate={br} delay=.1n Setup for a transient simulation. .tran 0 1u 2n 10p .options plotwinsize=0 Best regards, Helmut |
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