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Pseudo-random Bit Sequence: V_PRBS

Symbol

Summary

V_PRBS is a voltage source in the form of a pseudo-random bit sequence.

Parameters

Name Description Unit Type Default
ID Voltage source ID Text V1
RATE Symbol rate Frequency 1 GHz
NSYMB Number of symbols   16
SAMP Samples per symbol   8
BITW Number of bits in symbol   1
HI High signal level Voltage 1
LO Low signal level Voltage 0
*TR Rise time Time 0
*TF Fall time Time 0
TYPE Signalling format   NRZ1
WINDOW Window type   DEFAULT2
SEED Random number generator seed   -1

* indicates a secondary parameter

[1] Allowed formats are return to zero (RZ) and non-return to zero (NRZ).

[2] Window type options are none (NONE), Lanczos (DEFAULT, ref [1]), Triangular (TRIANG), Hanning (HANN), Hamming (HAMM), and Blackman (BLACK).

Parameter Details

BITW. Can be used to apply multilevel PRSB signals. The number of levels is equal to 2BITW. Levels are equally spaced between HI and LO.

WINDOW. The PRBS sequence must be represented in the frequency domain for the purposes of harmonic balance analysis. To control overshoot (Gibbs phenomenon) the sequence is windowed prior to simulation. Note that windows attenuate high-frequency components and therefore induce a finite rise and fall time. With the exception of the triangular window, the windows are listed in the order of smaller overshoot/longer rise time.

TR and TF. Rise and fall times are strongly influenced by the window type and the number of samples used to represent the sequence (the product of SAMP and NSYMB). If precise rise and fall times are critical to the application, use WINDOW=DEFAULT and increase SAMP as necessary.

NSYMB. There are no a priori limitations on the number of symbols in the sequence. However, the number of frequencies in the Fourier representation of a PRBS sequence equals one half of the product of NSYMB and SAMP, so longer sequences result in longer simulations.

NSYMB and SAMP. The product of these two parameters must be a power of 2 or an error is produced.

SEED. If less than zero, the current tick count of the system clock is used for seed.

Implementation Details

Harmonic balance options and project frequencies (or nonlinear frequencies) are ignored for the purposes of simulation with V_PRBS.

The fundamental frequency is determined by RATE/NSYMB.

The number of frequencies simulated is determined by NSYBM*SAMP/2 +1. (The +1 is for the DC component.)

The maximum frequency in the spectrum is determined by RATE *SAMP/2.

The number of frequencies is determined by NSYMB and SAMP. Likewise, the fundamental frequency is determined by RATE and NSYMB and is in no relation to the project and nonlinear frequencies.

NOTE:

You can use Veye and Ieye measurements to display eye diagrams in conjunction with V_PRBS simulations.

Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

References

[1] R.W. Hamming, Numerical methods for scientists and engineers, pp 534.

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