Issue link: https://resources.pcb.cadence.com/i/1480188
APPLICATION NOTE 1 In communications work, the eye display is frequently used to illustrate the voltage and timing margins present in a system transmitting digital data. In an eye display the signal is shown with a time axis that is a small number of data periods long. The signal wraps from the right edge of the display back to the left edge, thereby depicting a large number of overlapping data periods. If a random bit pattern is simulated and then displayed in this way, the required margins can be seen as the opening in the eye on the display. Probe's macro feature can be used to create a sweep function that implements the wrap feature required. You can then change the time axis variable from time to this sweep function to obtain an eye display. To use the macro feature, select Macros from the Trace menu in Probe. Then type the following three macros: pi=4*atan(1) mod(a, b) = (b)*(atan(tan(((a)/(b))*pi-pi/2))+pi/2)/pi eye_sweep(p, d) = mod(time+(p)/2+(d), p) - ((p)/2+(d)) The first macro (pi) calculates the value of π. The second macro (mod) is a floating-point modulo function, implemented using the tangent and arctangent functions. The third macro (eye_sweep) implements an eye sweep function; the display is centered at one half the period (p/2), plus a time delay (d). To use the macros, simply change the time axis variable from time to eye_sweep(p, d). In this function, p is the data period of the system (or a multiple of it), and d is the time interval by which the start of the display is delayed. As an example, consider a simple system that sends a randomstream of bits through an Analog Behavioral Model of E2 device. The bit stream is generated by a ten-bit shift register (U1) with feedback provided by an XOR gate (U2). The signal is processed by a tristate buffer (U3) and a E2 device to generate standard noise. This arrangement generates a pseudo-random sequence 1023 bits long. The simulation runs for 5 usec. Following is the schematic diagram of the circuit: Figure 1: Schematic diagram of random generator.