Yet More on Clocks

Peter and John

New bias network for AC coupled BCO

2V5

33k33k

Original version left 120mV DC bias between the two inputs

Alternative shown suggested by Dave Nelson and Dieter Freytag (SLAC)

Implemented on the stavelet by PWP (for H0 only – others unchanged) using 0603 components mounted vertically

How did we do?

H0 post blocking C, 68R ET, 100R BT H0 Recovered BCO, 68R ET, 100R BT

=> Looks great!

Next: vary back termination (0R < X < 100R) to explore margins

H0: BCO pre blocking C, 56R ET, X1 BT H0: Recovered BCO, 56R ET, X1 BT

H0: BCO pre blocking C, 56R ET, X2 BT H0: Recovered BCO, 56R ET, X2 BT

H0: BCO pre blocking C, 56R ET, X3 BT H0: Recovered BCO, 56R ET, X3 BT

H0: BCO pre blocking C, 56R ET, X4 BT H0: Recovered BCO, 56R ET, X4 BT

Can we predict amplitude at capacitor inputs, using MLVDS driver, after 24 drops?

5 10 15 200

100

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Data (56R/100R)Fit

Drop number

380mVAmpl

itude

(mV)

Crystal Ball Time

• For a 24 drop stave built to the same tape geometry, we can extrapolate the stavelet data to predict the amplitude at the end of the BCO bus– Predict 380mV, 56R end term, 100R back term

• We have tested the BCC board with the new bias network for several input amplitudes– 340mV gives 51.8% duty– 186mV gives 52.3% duty– 120mV gives 54.6% duty (limit for ABCN)

• Prediction– A stave using BCC V2 with the modified circuit should work just

fine! Even looks like we have a factor >2 safety.

This looks great – but...

• Caveat– Need to try a chain of many boards with the new circuit to

confirm this, not just one– Modifying the card on the stavelet was very tricky, it would be

much safer to do this with an alternate“test vehicle”– Any volunteers with suitable facilities?– We could maybe replace the BCC boards on the stavelet with

new ones?• I would strongly recommend this be tested before any

decision be made to leave BCO clock regeneration out of BCC V3.

• Having said that – it looks like we won’t need it ;-)