PSS and PNoise

1. PSS: periodic steady-state

Using Harmonic balance (in the frequency domain): 1)simulating weak non-linear circuits; 2) handling frequency dependent components

or shooting (in the time domain): highly non-linear circuits with sharply rising and falling signals;

Determining the periodic oeperating point for the circuit, which can be later used for PAC, PXF, PNOISE, or PSTB.

1.1 Application

Autonomous circuit: like OSC (specify a pair of nodes p and n; specify an estimate of teh osc period)

Driven circuit: like amplifiers, filters, and mixers (specify the analysis period or fund freq)

1.2 Two phases

1) Initial transient phase: initialize the circuit

   a. 1st interval: tstart ---> tonset (onset of periodicity, min time for all sources are periodic)

   b. 2nd interval: optional user-specified stabilization interval, length tstab

   c. 3rd interval: one period for driven circuits, or 4x period for autonomous circuits

2) shooting or harmonic balance phase: compute the periodic steady-state solution 

1.3 Engine

1) Harmonic balance: solves in frequency domain and uses an ifft to calculate the time-domain response.

2) Shooting: calculates the settled time-domain waveforms and calculates the frequency-domain content using a Fourier transform.

**Pss needs to simulate an integer number of cycles. This limit the practical app of pss to multi-input freq having high common multiple freq (beat freq). For example, if 1GHz and 1.1GHz frequencies are applied, the beat frequency is 100M. Solving for the fifth harmonic of the 1.1GHz input requires that 55 harmonics be calculated. This is a reasonable problem for pss. If the inputs are 1GHz and 1.001GHz, 5005 harmonics are needed to calculate through the fifth harmonic of 1.001GHz.**

2. PNoise                                                                                                                                            PNoise analysis is similar to the conventional noise analysis, except that it includes frequency conversion effects. Hence, it is useful for predicting the noise behavior of mixers, switched-capacitor filters, and other periodically driven circuits.                     

2.1 Noise type

1) timvaverage: average noise power over the LO or clock cycle.

2) sampled(jitter): an instantaneous measurement of the noise at the threshold crossing in the pss analysis.

Noise in high state and low state does not matter. The only time the noise matters is at the exact time where the trigger event is generated. The noise is likely to be larger in the switching interval.

Since the RMS noise voltage is calculated, the timing uncertainty is one standard deviation from the ideal crossing time.

Reference:

http://web.engr.uky.edu/~elias/tutorials/Spectre/spectre_refManual.pdf

Spectre® Circuit Simulator and Accelerated Parallel Simulator RF Analysis in ADE Explorer User Guide

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