Transcript TOF Front End electronics o Reminder: TOF requirement o Time Walk correction o Open options • Constant Fraction Discriminator • Charge Measurement • Time over Threshold.

TOF Front End electronics
o Reminder: TOF requirement
o Time Walk correction
o Open options
• Constant Fraction Discriminator
• Charge Measurement
• Time over Threshold Measurement
Feb 2006
Jean-Sébastien Graulich
Slide 1
TOF Requirements

Time resolution:
50-70 ps resolution
-> Choice of TDC: CAEN V1290
(25 ps LSB, >1000 Evt buffer)

Particle rate
~ 2 MHz in TOF0

Feb 2006
Charge measurement is not required
Jean-Sébastien Graulich
Slide 2
Time Walk Correction

Timing is affected by the signal amplitude
Time Walk Correction
Time
Walk
Thresh.
Time over threshold

2 Usual Solutions:


Feb 2006
Use Constant Fraction Discriminator (CFD)
Measure amplitude and correct
Jean-Sébastien Graulich
Example from Harp
Slide 3
Possible Options
Option 1. Constant Fraction Discriminator (CFD)
The time walk is corrected automatically in the discriminator
Threshold value depends on the amplitude
Advantage: Easy Cabling and No ADC

PMT

Feb 2006
CFD
TDC
Trigger Logic
Drawback


BNC Cable
No information at all on the charge (Energy Deposit)
Cost: TDC +
~ 125 EUR/ch (CFD)
Jean-Sébastien Graulich
Slide 4
Possible Options
Option 2. Measure the Charge with a QDC
Advantage: More Precise and
Good Charge Measurement
Drawback





General MICE ADC problem (No suitable QDC exists yet!)
Requires Splitters
More cabling
DISCRI
PMT
BNC Cable
TDC
Splitter
Trigger Logic
Cable
Delay

Feb 2006
QDC
Gate
Signal
Cost: TDC +
~ 125 EUR/ch (DISC)
~ 200 EUR/ch (QDC)
~ Delay Cables (~20 m/ch)
(Assuming free splitters)
Jean-Sébastien Graulich
Slide 5
Possible Options
Option 3. Measure the Charge with any available Solution


Feb 2006
Same Advantages and Drawbacks as 2.
Cost: TDC + ~ 125 EUR/ch (DISC)
~ ??? EUR/ch (ADC)
~ Delay Cables (~20 m/ch)
(Assuming free splitters)
Jean-Sébastien Graulich
Slide 6
Possible Options
Option 4. Measure the Charge with Time Over Threshold Principle

Advantage:
PMT
Easy Cabling and
Charge Measurement (not linear though)
Good Precision for Time Walk Correction
TDC
NINO
Width ~Charge


Feb 2006
Trigger Logic
NINO = ASIC developed by CERN/MIC for Alice TOF
Discriminator with ToT “proportional” to the Charge (at low amplitude)
Proven technique, providing 50 ps resolution (IEE TNS Vol 51-5 (2004) 1974-1978)
Very Cheap: 2 EUR/ch
Drawback


Rising edge + Trailing edge
Time Measurement
Requires Board development !
Cost: TDC +
Discri. board production (~50 EUR/ch)
Jean-Sébastien Graulich
Slide 7
Plan



Feb 2006
Options 1. and 2. Will be tested in
June/July at BTF
Additional Test with TDC CAEN V775 to
allow comparing with previous results
(HARP)
Options 3. and 4. are under investigation
Jean-Sébastien Graulich
Slide 8