1 LHCb CALO commissioning meeting 28.08.08 Anatoli Konoplyannikov /ITEP/ Proposal of the ECAL CW...

1LHCb CALO commissioning meeting 28.08.08 Anatoli Konoplyannikov /ITEP/

Proposal of the ECAL CW base modification +Anatoli, Michail

( Michail Soldatov is electronics expert, one of the CALO HV systems designer IHEP, Protvino)

Introduction

• As was discovered, the ECAL CW base design has some features lead to a HV output non-stability and noise impact to a PMT anode.

• An additional PSPICE simulation of the ECAL CW base has been done and a modification proposal for detailed study is suggested.

• The scope test of the ECAL CW shows a charge pick-up on the OA inputs, an integration chain (same as in HCAL CW base design) has been added. The proposed for ECAL circuit now is the HCAL circuit with optimized RC integration chain.

• Five modified ECAL CW bases were studied with scope and showed the same behavior.

• Additional solutions have been simulated and results are shown in backup slides:

1. CW base version working with OA operated in switching mode, but in linear regulation mode.

2. An optimized ECAL version with OA operated between linear and switching mode.


Proposal of the ECAL CW base modification +Technical details.

The CW base circuit that we study has two operational modes:

1. OA in linear mode and it controls the discharge current throw the transistor Q1. Q1 operates in switching mode with a pumping frequency (60 kHz). Few years ago the HERA-B CW base design has been optimized for HCAL application working in linear mode. Two capacitors with not clear functional meaning have been removed and internal to OA integration chain added for the OA regime stabilization.2. OA works in switching mode (some designers are using a digital comparator integrated circuit instead of OA). Q1 operates in switching mode too but with different frequency defined by a feedback delay. There is a sub-mode for this operational mode.When a charge is applied to the OA input through some capacitance, the circuit works in switching mode with 60 kHz frequency, but in addition a low frequency is presented. This is an original ECAL CW base design.

Analysis ECAL CW base behavior, PSPICE simulation and scope study of the five CW bases with tubes show that for current ECAL CW base implementation the linear mode is preferable.


Proposal of the ECAL CW base modification +

Disadvantages of the switching mode operation for the current ECAL CW base design are following:

• HV output dependence versus LV power supplies;

• HV output voltage shift, due to a charge injection to the OA input;

• For CW base operating in linear mode the multiplication coefficient Coe must be:

HVout = Coe*Uctrl + Ushift,

Coe = (Rfb / (Rin * 4)) * 22 (= 425.8),

where Rfb is feedback resistor of 4800 k, Rin is 62 k.

HCAL

• An addition the low frequency oscillations of the HV output could be appeared for some values of the control and middle voltages (see slides 18,19)

My report “Status HV System based on CW base for HCAL Application”, on LHCb meeting 21.05.03

U Photocathode vs U control for five CW HCAL bases

y = 427.6x + 8.95

500

700

900

1100

1300

1500

1700

1900

2100

0 1 2 3 4 5 6

U control V

U p

h V

k21

k22

k23

k24

k25

Linear (k21)


Proposal of the ECAL CW base modification +PSPICE Simulation conditions:

• The main point of the simulation is study the behavior of the HV Output from different factors.

• Few factors affected on HV output were applied in simulation:

1. Control voltage change from 1 V to 1.5V (in time 55 ms);

2. Output load current change from 0 to 10 mkA (in time 80 – 90 ms);

3. LV power change from (+-) 5 V to (+-) 6.5 V (in time 100 – 130 ms);

4. Parasitic capacitance from switching transistors to OA input is simulated by capacitor C20 = 0.1 pF.

Next slides illustrate the simulation results:

Slide_6 is an overview of the all simulation time.

Slide_7 is zoom of the time interval when a control voltage changes.

Slide_8 is zoom of the time interval when an output load current changes.

Slide_9 is zoom of the time interval when LV power changes.

Slide_10 is zoom of the time interval with detailed view of the signal shapes of some internal points.



10

-5V -> -6.5V5V -> 6.5V

1V -> 1.5V

100 V

HV Output

Simulated CW base circuit diagram

Parasitic capacitance simulated a PCB cross talk



Overview of the simulation time



Control voltage change from 1 V to 1.5V (in time 55 ms);



Output load current change from 0 to 10 mkA (in time 80 – 90 ms);



LV power change from (+-) 5 V to (+-) 6.5 V (in time 100 – 130 ms);



Zoomed time interval with detailed view of the signal shapes of some internal points.



OA output signal and Q1 collector comparison

Scope measurement and simulation result

Conditions: HV_out = 480 V, I_load ~ 0 mkA.



Scope measurement and simulation result

OA output signal and HV ripple after CW fifth stage comparison


Ripple < 80 mV

Ripple < 100 mV



Scope measurement of the chained tubes

Pumping frequency correlation for chained tubes. Green trace OA output of CW 1.

1

2

3

Correlation between CW_1 – CW_2

Correlation between CW_1 – CW_3

Not Correlated

Correlated



CW base output ripple for three sequentially connected tubes is about 1.5 V pick to pick, but with high load current.

Scope measurement




ECAL CW base modification:Six points of soldering

• Add R16 = 5.6 k in serial with C5

• Remove wire and add R2 and C1 (see circuit diagram)

Add wire to connect two ground lines

Remove C17Remove C2



Conclusion

The ECAL CW base modification, proposed by me and Michail, is the HCAL design with optimized integration chain.

The circuit simulation is very good matched with the scope measurements.

Simulation shows that C1*R2 time constant could be in wide range from 5 to 30 mks.

Six soldering operation will be needed for one base modification, but in my opinion, much more time will be needed for dismounting and mounting PMTs.

There is good indication that modification of the ECAL design to HCAL one allows to have the same CW performance. Fifteen hundreds (quota of ECAL amount) of the HCAL CW bases are working now.



Low frequency oscillation of the near original ECAL base.

Simulation of a CW base version working with OA operated in switching mode.

Simulation of an optimized ECAL version with OA operated between linear and switching mode.


Low frequency oscillation of the near original ECAL base

OA is operating in switching mode with low frequency. C1=2 pF; R2=50k; C21=0 pF; c17=1nF

CW base Simulation.


OA is operating in switching mode with low frequency. C1=2 pF; R2=50k; C21=0 pF; c17=10nF

Simulation and scope test comparison.

Low frequency oscillation of the near original ECAL base



OA is operating in switching mode.

C1=2 pF; R2=50k; C21=2 pF; c17=0







F = 30 kHz


F = 60 kHz





Simulation of an optimized ECAL version with OA operated between linear and switching mode

Two cases were simulated:

C21 = 300 pF; C17 = 47 nF; C1 = 0; R2 = 0;

C21 = 300 pF; C17 = 47 nF; C1 = 100 pF; R2 = 50 k;


C1 = 100 pF





C1 = 0.0001pF




Conclusion





Study to be continued.

Date post:	16-Dec-2015
Category:	Documents
Upload:	clara-warren
View:	222 times
Download:	1 times

1 LHCb CALO commissioning meeting 28.08.08 Anatoli Konoplyannikov /ITEP/ Proposal of the ECAL CW...

Documents