SLLA579 January   2022 ISOUSB211

 

  1.   Trademarks
  2. 1PCB Trace Insertion Loss and Inter-Symbol Interference
  3. 2Transmitter Pre-Emphasis and Receiver Equalizer
  4. 3Selecting an Optimal Pre-emphasis for Your System
  5. 4Eye-Diagrams for 6 inch to 4 feet Traces with all Nine Pre-Emphasis Settings for USB 2.0 Near-end Eye-mask
  6. 5Eye-Diagrams for 6 inch to 4 feet Traces and 5m Cable with all Nine Pre-emphasis Settings for USB 2.0 Far-end Eye-mask
  7. 6Using Receiver Equalizer and Transmitter Pre-emphasis for Channel Loss Compensation Simultaneously
  8. 7Summary

4 Eye-Diagrams for 6 inch to 4 feet Traces with all Nine Pre-Emphasis Settings for USB 2.0 Near-end Eye-mask

Figure 4-1 through Figure 4-6 show the eye-diagram measurements with Figure 3-1 setup that uses the transmitter pre-emphasis to compensate for the trace loss. The receiver equalizer is set to 00 throughout the measurements since the loss between the transceiver and ISOUSB211DPEVM is ignorable. The first subplots of each figures show the measured eye-diagrams of FR-4 traces without including the ISOUSB211DPEVM. It is obvious that the system fails the near-end eye-mask even with a 6-inch trace length. We use the EH multiplied with EW as the metric to justify transmitter pre-emphasis performance as shown in Figure 4-6.

Figure 4-1 NE TX_PE 6-inch Trace
Figure 4-3 NE TX_PE 2-feet Trace
Figure 4-5 NE TX_PE 4-feet Trace
Figure 4-2 NE TX_PE 1-feet Trace
Figure 4-4 NE TX_PR 3-feet Trace
Figure 4-6 Summary of EH*EW Metric for NE TX_PE 6-inch to 4-feet Traces

Figure 4-7 through Figure 4-12 show the eye-diagram measurements with Figure 3-2 setup that uses the receiver equalizer to compensate for the trace loss. The transmitter pre-emphasis is set to 00 throughout the measurements. As mentioned, due to the fact that the On-Off Keying circuitry in the isolator of the ISOUSB211 generates a fresh copy of the signal based on the logic of input signal, this cannot justify the receiver equalizer performance by gauging the eye-height (EH). The output jitter of the ISOUSB211 is additive from the uncompensated input jitter and the jitter generated by the On-Off Keying circuitry. We can pinpoint the optimal receiver equalizer settings for each trace length by judging the eye-diagram that has the wider eye-width (EW) or lowest jitter as shown in Figure 4-12.

Figure 4-7 NE RX_EQ 6-inch Trace
Figure 4-9 NE RX_EQ 2-feet Trace
Figure 4-11 NE RX 4-feet Trace
Figure 4-8 NE RX_EQ 1-feet Trace
Figure 4-10 NE RX_EQ 3-feet Trace
Figure 4-12 Summary of EW metric for NE RX_EQ 6-inch to 4-feet Traces