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Pseudo-random Bit Sequence: PORT_PRBS



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


Name Description Unit Type Default
P Port number   0
Z Termination impedance Resistance 50 ohm
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 Signaling format   NRZ1
WINDOW Window type   DEFAULT2
SEED Random number generator seed   -1
*TONE Tone number   1
PIN_ID Name identifier for pin Text  

* 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. This parameter may 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 known 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 issued.

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 PORT_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 not related to the project and nonlinear frequencies.

When BITW is 1, the binary sequence generated is such that there are NSYMB 1 bits and NSYMB 0 bits. A Wichmann-Hill random number generator is used to determine which positions in the 2*NSYMB bits are to be set to 1, with the numbers generated by the random number generator corresponding to the bit positions. Random numbers are generated until NSYMB unique positions out of the 2*NSYMB available positions have been selected. The bits at these positions are set to 1.

When BITW is greater than 1, a Wichmann-Hill random number generator is used to generate 2*NSYMB numbers in a range of 2BITW discrete values. The generated values are then used to determine the level to output for each symbol.

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

If PIN_ID is not empty, text displays on the pin when it is instantiated as a subcircuit.


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.


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

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