# Presentation: 659624

## Upgrades of the Luminosity Monitor Electronics:Status of the Readout Electronics 

- _J-F. Bêche_, J. Byrd, P. Denes, M. Monroy,
- A. Ratti and W. Turner

## Outline

- Baseline bounce Problem
- Baseline recovery problem
- Shaper Development
- Preamplifier Findings
- Future Developments

## Baseline Bounce Problem (1)Beam Data

## Baseline Bounce Problem (2)

- The baseline bounce is associated to an experimental grounding problem:
- Bounce is setup related (not happening in the laboratory)
- Chamber vessel is currently not electrically isolated from the beam pipe during the beam experiment.
- Better isolation and better shielding needed.
- Move the DAQ equipment inside the ring to have a single point ground connection (remote control of DAQ needed).

## Baseline Recovery Problem – Beam Data

- Undershoots

- Recovery problem

- Pile-up Effect

## Baseline recovery

- The problem is known as the Pole-Zero problem (PZ) and is caused by the decay of the preamplifier signal.
- Cancellation can be introduced at the shaper level to compensate for the loss of signal.
- Some channels have an overshoot and some others an undershoot.
- The current implementation of the shaper has a PZ compensation with a very limited range, that does not cover the application’s needs.

## Design of a new shaper with PZ Cancellation

- The pseudo-gaussian shapers considered implement the following function:
- n is the order of the filter. For this application n=4.
- Two implementations have been studied:
- Using Current Feedback Amplifier:  	built and tested
- Using Voltage Feedback Amplifier: 	not assembled yet

## Sallen  Key Shaper – SK4 – Model 

- 2-pole SK structure

- PZ cancellation
- (Potentiometer)

- 800MHz CFA

## SK4: Single Pulse Response (simulated)

- SK4: Single Pulse Response (simulated)

- Preamplifier Model

- SK4 Response

- 20ns

## SK4: 40MHz Burst Response (simulated) 

- SK4: 40MHz Burst Response (simulated)

- Preamplifier
- Model

- SK4 Response
- With PZ
- adjusted

- No Pile-up and
- no Recovery Problem

- 20ns

- 25ns

## PZ Problem: Single Pulse Response(Simulated)

- Preamplifier Model

- SK4 Response
- PZ not adjusted

- 20ns

- Recovery Problem

## PZ Problem: 40MHz Burst Response (Simulated)

- PZ Problem: 40MHz Burst Response (Simulated)

- Preamplifier
- Model

- SK4 Response
- With PZ _not _
- adjusted

- 20ns

- Pile-up Effect and
- Long Recovery

- 25ns

## SK4 Shaper:Step Response (Measured)

- 20ns

- Tp=8ns

## Preamplifier + SK4 Shaper:Laboratory Setup

- Cd = 82pF (Equivalent to Chamber)

## Preamplifier + SK4 Shaper with Cd = 82pF

- 40ns

- Slow rise-time

- Break in the slope and broadening of the pulse at the base

- SK4 Response (*)

- (*) In the board implementation, an inverting driver stage follows the shaping network
- (Gain and offset adjustment).

## Preamplifier Signal with Cd=82pF

- Tr= 10ns @ Cd=82pF
- Tr= 7ns @ Cd=0pF

## Preamplifier Findings

- In a classic preamplifier/shaper circuit, the dominant pole of the system is set by the shaper:
- However, with the current implementation of the preamplifier, the dominant pole is the one of the preamplifier.
- The peaking time of the current preamplifier with Cd=82pF is 14ns, which makes the return to baseline in less than 25ns impossible (unipolar shaping).
- The preamplifier’s response is too slow for the current application.
- The performance of the current preamplifier is limited by its gain-bandwidth characteristics.
- The bump on the trailing edge of the signal is an indication of impedance mismatch  (cold termination not fully effective)

## Pole-Zero Cancellation:Response to a burst (Cd=82pF)

- Preamplifier + SK4 Shaper

- Preamplifier + Old Shaper

- Recovery Problem

- No recovery problem

## Conclusions

- The SK4 shaper response to a step function shows that the pulse can be made shorter than 25ns, if the preamplifier signal has the appropriate characteristics.
- Potentially no need for deconvolution.
- The Pole-Zero cancellation is effective in bringing the signal back to the baseline with neither undershoot nor overshoot.
- The performance of the current system is limited by the preamplifier’s characteristics.
- In collaboration with Pavia, we need to improve the preamplifier’s performance regarding:
- The “cold” termination equivalent impedance
- The rise-time of the amplifier

## Future Work

**Solve the Preamplifier problem:**
- Improve current structure
- Study different solutions
**Package the front-end electronics**
**Verify the functionality of the electronics in the laboratory and with the chamber in the beam.**
**Data acquisition and system integration:**
- Recent talks at CERN about Data Acquisition Board
- DAB used by CERN for LHC machine control
- Data Processing
- Prototype Development of a “mezzanine” (daughter) board specific to LUMI
- Development of the firmware for digital data processing
- Installation