1. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 1 PHOS APDs The APDs are very sensitive to Bias/Cooling variations within the working ranges HAMAMATSU S8664-55 Si APD (Uncorps modification of the APD – S8148) Full PHOS quantity = 56 x 64 x 5 = 17920 pcs. Working PHOS Bias range = 300V – 400V Working PHOS Temperature = -25° C Breakdown Voltage Dark Current Terminal Capacitance Gain APD Critical Parameters

2. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 2 Why PHOS has need for individual APD BIAS Control ? So we must control the effective PHOS channel gain factors to compensate the following scatterings: Wide scattering of the APDs gain factors ; Extreme sensitivity of the APDs gain to bias for PHOS working temperature condition (-25C); Gain scattering of the Preamps; Light yield scattering of the PWO Crystals; Scattering of the APD-Crystal gluing transparency. PHOS takes part in ALICE Trigger by generation of partial analog energy sums. Individual APD BIAS Control has the benefit to refuse of APD’s selecting, grouping and pretest costs.

3. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 3 HV (V) APD BIAS LV-HV regulation range LV (V) DAC code 400 300 200 100 250 0 2.5 50 0127255 Support voltage level Work HV range

4. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 4 LV-HV 8 8 8 8 32 APDs T-card LV-HV 8 8 8 8 8 DACs 400V 8 DACs 8 DACs 8 DACs FEE SU Micro controller PC To other SUs (512 channels) RS-232 Interface SPI Interface T-card PHOS Cold zone General structure of Beam Test-2003 APD BIAS Control

5. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 5 Principle of Serial Peripheral Interface (SPI) SPI is a synchronous serial data protocol for a high bandwidth (1 megabaud) network connection amongst CPUs and other devices supporting the SPI.

6. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 6 Principle of DACs Daisy-Chaining 8DACs

7. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 7 LV-HV Regulator (I.Sibiriak) Minimum components schematic 400V U ref LV from DAC Output (0-5V) AD8544 KPC452 HV to APD (~250-400V)

8. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 8 Test Beam 2003 Kurchatov FEE view 8-Channels APD BIAS Regulator zone

9. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 9 Long-Term and Temperature Stabilities Test Results HV Long-Term Instability within 3 days < 0.1% HV Temperature Instability for 18 C° – 32 C° range < 0.1%

10. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 10 256 Channels PHOS GAINs Distribution (pre-selected APDs) Without APD BIAS Control

11. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 11 9 PHOS Central Channels (Wide Electron Beam) With APD BIAS Control 8-bit DACs (MAX5258) 4% peak selection accuracy

12. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 12 Evolution of APD BIAS Control after Test Beam 2003 1) More gain accuracy - from 4% (8-bit DACMAX5258) to 1% (10-bit DAC MAX5308); 2) Instead of Microcontroller use Readout Controller Unit (RCU) resources and Board Controller (BC) for DAC control (from ALICE TPC FEC project); 3) Separate control by 32 APD channels (one FEE); 4) SPI simulation on BC FPGA.

13. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 13 LV-HV 8 8 8 8 32 APDs T-card LV-HV 8 8 8 8 8 DACs 400V 8 DACs 8 DACs 8 DACs FEE SU T-card Board Controller (FPGA) SPI I2C-SPI RCU I2C PHOS Cold zone ALTRO

14. April 27, 2004 ECAL meeting, Giessen A.Vinogradov Kurchatov Insitute, Moscow 14