Presenter: Allen DuncanApril 10, 2003

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Highlights of the Last Week

• Tested Receiver without optical link

• Used Al shield to determine EMI presence

• Conducted FFT analysis on Power Supply

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Review of Last Presentation•Better Results at 5 dB atten. when transmitter on.

•Is the signal we see crosstalk?

5 dB attenuation with TX OFF 5 dB attenuation with TX ON

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Remove Optical Link

• Q: Will Eye diagram remain w/out optical link?

– A: YES

No Optical Link PRBS7 No Optical Link D21.5

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Removing Optical Link• Q: Eye diagram remains, What does this

mean?– A: Cross-talk between Transmitter and Receiver

is sufficient enough to create its own Eye

• Q: Does this cross-talk cause a problem in the functionality of the tranceiver?– This is yet inconclusive. A more sensitive PD,

or stronger signal may overcome such X-Talk.

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X-Talk experiments: Shielding• Shielding between entire TX and RX

Aluminum Shield Setup between TX and RX

Eye Diagram with RX/TX shield

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X-Talk experiments: Shielding• Shielding specific components

No Shielding

VCSEL shielding

SMA shielding

PD shielding

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X-Talk experiments: Shielding• Shielding Conclusions

– More evidence there is EMI between RX and TX– X-Talk Eye disappears only when RX and TX

modules are completely shielded– When PD is shielded some degradation of

signal is obtained but Eye is still visable

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Power Supply Noise• At least 2 frequencies present

Noise on PS – at least 2 freq present Zoom of high frequency part of noise

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More about noise and crosstalk• Significant noise

similar to that on the Power Supply was measured in the air as well

• Moving Foil Shield around produced weird results Eye diagram with Foil shield in random position

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FFT Analysis• Spikes at several Frequencies

– ~3 MHz– ~330 MHz– ~660 MHz– ~1.25 GHz

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Plans for the Coming Week

• Unconnectorized PD – Alignment tolerance

• Find and purchase more sensitive PD

• Determine solutions to no signal at 5 dB

• Determine ultimate role of X-Talk in disturbance of signal