This is the information presented at the collaboration meeting with
decisions and updates shown to Jan 31, 2001.

John Schaapman                     Ph: 780-492-3043
Centre for Subatomic Research     Fax: 780-492-3408
University of Alberta            NOTE: new area code
Edmonton, AB
CANADA       T6G 2N5

 Charge Readout System - Jan 24, 2001 

                          #  Updated  Jan 31, 2001



 Characteristics of LeCroy MQT300A Charge to Time Converter 



  Maximum full scale negative charge input is 2,620 pC. This charge

is captured simultaneously in  three ranges during the gate.

  At the maximum sensitivity ramp current, ( Iramp = 320 microamp )

the conversion factors for the  ranges look like this:



HIGH 2620   pC F.S.  0.78 ns/pC 1,282 fC per ns = 2,040 nsec max

MID   326.5 pC F.S.  6.25 ns/pC   160 fC per ns = 2,040 nsec max

LOW    40.8 pC F.S. 50    ns/pC    20 fC per ns = 2,040 nsec max



   To this must be added the residual pedestals for each range:

                  HIGH 500 ns, MID 650 ns, LOW 800 ns 



   The ramp current can be increased by up to a factor of 4.375 

( 1,400 microamp ) to reduce the  conversion and pedestal time at

the expense of time resolution.

 

Deadtime @ F.S. for MID range, not counting TDC conversion time



  Iramp = 320 microamp 

#  normal operation    2,040   nsec + 650   nsec = 2,690   nsec

    Fast clear                                       900   nsec

  Iramp = 1,400 microamp 

   normal operation      466.3 nsec + 148.6 nsec =   614.9 nsec

    Fast clear                                       900   nsec



Opamp Stage estimate of Qin to MQT300A using inverting opamp cct.



  The Burr Brown OPA689 opamp is set for an inverting gain of six.

A rough estimate of the input charge  provided to the MQT300A with

input resistance set to 200 ohms can be made by applying  VTX peak 

output values over the pulse width of 20 nsec.

Qin = Av * VTXpeak * dt / Rin

Qin = 6 *  88 mv * 20 ns / 200 ohm =  52 pC

Qin = 6 * 300 mv * 20 ns / 200 ohm = 150 pC 

  This puts the input signals into the MID range of the MQT300A.



TDC counts and actual deadtimes .



Counts = Qin * MID range conversion factor / TDC time per count 

deadtime =(signal counts + pedestal counts)*TDC nsec per count



      Iramp                      signal pedestal  total    deadtime

 52 pC input

#  320 microamp

 52 pC * 6.25 ns/pC/0.5 ns/count =  650 1,300 1,950 cnts   975 nsec

 1,400 microamp

 52 pC * 1.43 ns/pC/0.5 ns/count =  148   297   445 cnts   223 nsec

150 pC input 

#  320 microamp

150 pC * 6.25 ns/pC/0.5 ns/count =1,875 1,300 3,175 cnts 1,588 nsec   

 1,400 microamp

150 pC * 1.43 ns/pC/0.5 ns/count =  429   297   726 cnts   363 nsec



  The tradeoff is between TDC output resolution and deadtime and

can be adjusted with the resistor that  sets the ramp current.



#  We will likely use the maximum sensitivity setting since

deadtime is not a problem.

Description: Charge Readout System Jan 31 doc , Filename: ChargeReadoutSysupdtJan31.doc.txt

 Postamp Charge-to-time converter module  Jan 24, 2001

                                        *  Update Jan 30, 2001



1. GATE - The charge integration gate is common to all channels in

each  module and to all 12 modules in the experiment. Front panel

NIM input.

  * GATE changed to two inputs for groups of 8 channels so that an 

identical module can be used to read scintillator signals with two 

different gates.



2. Fast Clear - Common to all channels. It may not be used in this 

experiment. Front panel NIM input.



3. The charge converters will be fixed on one of three ranges with

three jumpers. ( Common jumpers for all channels on front panel,

 TTL ). They will not be changed once the experiment is set up.

 

4. Standard PAD type input and output connectors.



5. The output pedestals from the MQT300s exceed the minimum pulse 

width requirements of the TDC.



6. All outputs will fire with either a signal or pedestal pulse

for every gate  signal.

        * TDC will remove channels with no signal.



Control and Monitor



1. Control - Test Pulse same as PAD test pulse. To use it gate

signals will  need to be provided at the same time. Gate width

should be same as the experiment to keep the pedestals the same.

The gate must close before the falling edge of the test pulse

trigger.



2. Monitor Six items similar to PAD: Temp, Vcc + 5v, Vee - 5.2 v,

Test  Pulse v, + 24 v, + 15 v.



    Number of Modules Required



   To read out 192 channels we need 12  16 channel modules. Three 

spare modules could read one plane for testing or 12 extra modules

could be used for testing of a complete spare target chamber.

 

*12 for chamber + 1 for scint. + 3 spares + 1 set of parts = 17. 

*20 boards will be made with MQT300A chips missing from 3 or 4.



    Initial Production

        We will build at least three modules so that we can test

them on one complete plane of target PC to finalize gain resistors

before producing the  rest.

   

* This module is now called the " PACT "- PostAmp Charge to Time.

Description: Postamp Charge Converter Jan 30 doc , Filename: PostampChargeConverterJan30.doc.txt

Created for the The Center for Subatomic Research E614 Project Projects Page.

Created by The CoCoBoard.