1. A Readout Electronics System for GEM Detectors
IEEE NPSS Real Time Conference 2009
A Readout Electronics System for GEM Detectors
Zhi Deng, Yinong Liu, Guanghua Gong
Dept. of Engineering Physics, Tsinghua University
IHEP, Beijing, China, May 10-15,2009

2. GEM Detectors
Tsinghua

3. Architecture of Readout Electronics
electrons
Readout pads
CASA
Commercial ADC
(10bit, ~10MSPS)
FPGA
(DSP)
DAQ
Detector
Analog Front-ends
Digital Back-ends

4. CASA: the Front-end ASIC
CSA
Gain Stage
1st Shaper
2nd Shaper
Variable value of C, giving different charge gain, together with matched size of the MOS transistor
A dummy shaper amplifier, transfer signals to differential
A fully differential amplifier, with class-AB output stage

5. Specifications of CASA
Input Charge fC
SNR for MIP
>20:1
Gain (Differential)
1-28mV/fC, adjustable
Shaping Time (t)
25-100ns, adjustable
Output Swing
2 V p-p, differential
Drive Load
10pF
Crosstalk
<1%
Power Consumption
<10mW/ch

6. Chip Performance Test Input Protection Circuits CASA in CPGA package
Power: 8.9 mW/ch
Crosstalk: <0.98%

7. Programmability
Programmable gain
Programmable t
Adjustable baseline

8. Noise Performance
Different gain
Different t

9. Linearity

10. With GEM detector COOL-X X-ray Generator (peak @~8keV) GEM detector
CASA and buffer chips

11. Sampling and DSP Board
Input Buffer
AD9212
CLK
Xilinx XC4VSX35

13. Sampled Noise Spectrum
Normalized Power Spectrum Density
Continuous
Frequency /Hz
f-3dB=100M

14. The Impact to SNR
no pre-filter
tr,preamp =5ns
with pre-filter

15. Test Results

16. Summary
A waveform sampling readout electronics system has been developed for GEM detectors, using a front-end ASIC and commercial ADC and FPGA chips.
The front-end ASIC has been tested and work successfully. The sampling and DSP board has been designed and will be tested soon.
The dependence of SNR with the sampling frequency has been quantitatively studied, which is very important for control of power consumption.