Accurate High Frequency Jitter Amplification Predictions in StatEye

In high-speed channels as the data rate increases, the time allocated for one data symbol, (unit interval: UI) decreases. As a result, when you inject single pulse with the width of UI the one end of the channel, the output at the other end of signal does not settle within an UI. This causes the interference of one symbol data propagation to multiple subsequent symbols. This effect is called inter-symbol interference (ISI). As the data rate increases, the magnitude of ISI increases because larger number of subsequent symbols are affected by one symbol. Now a days, ISI became one of the dominant causes of the deterministic jitter in high-speed channels.

In addition to ISI, there are multiple causes of adding timing uncertainties (jitter) such as random timing variation by thermal or flicker effect (random jitter: Rj), power supply noise induced jitter (PSIJ) and so on. When this jitter is added to the transmitter side, ISI causes additional side effect called jitter amplification. At transmitter side, when each logic transition edge is shifted by jitter, during signal propagation through the channel, ISI enlarges the effect of one timing shift to multiple subsequent symbols. As a result, total accumulated timing variation at receiver side due to ISI-ed jitter may become larger than injected jitter amount in transmitter side.

Conventionally, with StatEye analysis in PrimeSim-SPICE/HSPICE, jitter in numerical sequence was injected on the top of edge super positioned bit stream output. Although this way can take jitter amplification to some extent, it may underestimate the amplification when high frequency random jitter occurs with possible different polarity at any time.

To simulate the high frequency random jitter amplification with high accuracy, StatEye introduced additional transmitter side jitter injection mode which can be activated by TxJitter_Mode = 3.

In addition to the jitter amplification accuracy, TxJitter_Mode = 3 has an advantage that this flow can be applied to any superposition modes in StatEye while TxJitter_Mode = 2 requires bit stream response waveform generation in XTALK_TYPE = DDP.

Top: transient analysis. Eye width: 54.5 psec, runtime: 39.1 sec

Bottom: StatEye with TxJitter_Mode =3. Eye width: 54.5 psec, runtime: 4.3 sec.

Note that transient analysis-based eye diagram on the top was generated by processing time domain (*.tr0) waveform into colored probability density map.

As is shown, TxJitter_Mode=3 accurately predicts the jitter amplification with significant computational efficiency.