Development of CMOS CSA for Point Contact HPGe Detectors
Zhi Deng for HPGe detector group @
Department of Engineering Physics, Tsinghua University
Application of Germanium Detector in Fundamental ResearchBeijing, March 23‐29, 2011
Outlines
• Introduction
• CMOS CSA Design– Noise Optimization
– Reset
• Test Results
• Summary & Future Plan
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Introduction
• ULE HPGe Detector
2011/03/25 Application of Germanium Detector in Fundamental Research
The key technologies for lowering the energy threshold is using small capacitance detector and ultra low noise readout
Point-contact HPGe, ~1pF
3
• JFET vs. CMOS for small capacitance detectors
Application of Germanium Detector in Fundamental Research2011/03/25
C C C
ENCa e C
a K C a i
tot in
nw totF tot n
= +
= + +
det
2 12 2
22
32
ττ
tm, ns
As the detector capacitance goes down, the contribution from 1/f noise become non-dominant anymore!
4
• What is the limit for 1/f noise
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e.g., Kf = 10-25J, Cd=1pF ENCf ~ 5 e-
( )222
, 2
ff d g
g
f opt f d
KENC a C C
C
ENC K C
π
π
= + →
≈Borrowed from Paul O’Connor’s talk in FEE2006
Why not CMOS then?
CMOS CSA Design
• Noise Optimization
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PMOS for lower 1/f noise, with optimized size Adjustable bias current
for noise study
Pulse reset for dischargingSee the next slide
• Reset
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Pulse Reset 1 Pulse Reset 2
On Chip Off Chip
Charge Injector with opposite polarity
• Layout and test board
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250μm
200μ
m
Test Results
• Test Setup
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Shaper
Signal Generator
Oscilloscope
Vacuum chamber
Power Supply
BumpTemperature sensor
• Injected with test signals
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Rise time is about 30ns for 1.5m long cable
After shaper
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0 2 4 6 8 10 120
5
10
15
20
25
30
Shaping Time [μS]
ENC
[e]
T=25oCT=18oCT=10oCT=0oCT=-10oCT=-20oCT=-30oCT=-45oCT=-60oCSys@T=25oCSys @ T=-60oC
6.5e
11
• ENC
Summary & Future Plan
• A CMOS charge sensitive preamplifier has been designed for point‐contact HPGe detectors, with noise optimized for 1pF capacitance. Sub‐10e ENC has been achieved without detector. Testing with detector is undergoing.
• A second version chip has been designed and fabricated and it will also be evaluated soon.
• More deep study on cryogenic CMOS transistor model, long term stability…
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Thanks
The test setup has been done for the first prototype ASIC with the first prototype of point contact HPGe detector
