Design and Characterization of a Micro-Strip RF Anode for Large- Area based Photodetectors Orsay- Friday, June Hervé Grabas UChicago / CEA

Transcription

1 Design and Characterization of a Micro-Strip RF Anode for Large- Area based Photodetectors Orsay- Friday, June Hervé Grabas UChicago / CEA Saclay Irfu.

2 Outline Introduction Precise timing in physics experiments. MCP as a fast timing detector Large Area Picosecond Photo-Detector The role of transmission line readout Modeling RF transmission lines The stripline excitation Techniques and measurement tools The key parameters for RF anodes design Impedance Bandwidth Attenuation and crosstalk Geometry matching Conclusion PhotoDet - H. Grabas 6/15/12 2

3 Precise timing applications in physics experiments Time-of-Flight PET TOF Time of Flight calorimeter π/κ separation Vertex identification/pileup suppression PhotoDet - H. Grabas 6/15/12 3

4 Getting fast timing Photomultiplier Microchannel plate ~10cm <1cm The key towards fast timing detector: Reducing the size of the electron path in the Photo-detector reduces the jitter and increases the rise time of the signal. PhotoDet - H. Grabas 6/15/12 4

5 The Large Area Picosecond Photo-detector Create Large Area Fast and Low Cost photomultiplier. See LAPPD project at the Univeristy of Chicago. Stripline readout: ü Reduce the number of pins ü Avoid pins through the glass ü Reduce the cost 20x20cm Photocathode MCP 1 MCP 2 Anode striplines Dual-end readout PhotoDet - H. Grabas 6/15/12 5

6 The role of the transmission line anodes. Excitation of 3 adjacent striplines during electron shower collection Transmission lines: ü Collect charge ü Transmit pulses on both sides ü Preserve signal integrity PhotoDet - H. Grabas 6/15/12 6

7 Spatial resolution with RF anodes Fast timing is required (see E. Oberla talk). ~10 s psec resolution. Time of Arrival on both side PhotoDet - H. Grabas 6/15/12 7

8 Modeling and designing the stripline anodes Full time domain simulation of transmission line readout Go to the frequency domain Strip excitation Signal propagation Signal acquisition In the frequency domain PhotoDet - H. Grabas 6/15/12 8

9 Modeling the stripline Create equivalent model in the frequency domain of the electron showering. ü Model the electron distribution: ü Fourier transform: excitation ü Extract the bandwidth: For typical MCP: Bandwidth of signal ~ GHz PhotoDet - H. Grabas 6/15/12 9

10 Tools and techniques used for RF anode design Launcher ü Couple SMA cable & connector to stripline geometry. ü 10dB gain over the whole bandwidth with good launcher. ü RF field solver doesn t work use copper tape. Frequency measurement ü Use network analyzer. ü Direct measure of bandwidth. ü Identify resonance and absorption in the spectrum ü With TDR option identify bottleneck location in your design PhotoDet - H. Grabas 6/15/12 10

11 Designing the anode: the key parameters Impedance ü Match the input impedance of the electronics (50Ohms) Bandwidth ü Match the bandwidth of the signal. Cross-talk ü Reduce cross-talk as much as possible between strips. PhotoDet - H. Grabas 6/15/12 11

12 For an array of striplines: odd and even mode impedance. Even mode: crosstalk Increase pitch between strip (but reduce the covered area) Thinner strips RF strip impedance PhotoDet - H. Grabas 6/15/12 12

13 Measured impedance PhotoDet - H. Grabas 6/15/12 13

14 Bandwidth Modeling with filed simulators doesn t give usable results. ü Complicated modeling ü Very sensitive to model ü Time consuming and hard to understand Best tools: network analyzer & copper tape. ü Direct measurement. ü Immediate correction with copper tape. PhotoDet - H. Grabas 6/15/12 14

15 Bandwidth improvement Bandwidth 800MHz 3GHz ü 40 strips 30 ü Include fanout ü 50Ohms impedance PhotoDet - H. Grabas 6/15/12 15

16 Crosstalk Two adjacent striplines are both capacitively and inductively coupled. A wave traveling down the line induces a signal on its neighbor both in the forward and reverse direction. The magnitude of the crosstalk depends the strip spacing, impedance and dielectric used. PhotoDet - H. Grabas 6/15/12 16

17 Measured crosstalk Measurement of the crosstalk as a function of the strip number on the anodes More than 12dB of attenuation over the integrated frequency span from one strip to other, while having still 68% coverage. PhotoDet - H. Grabas 6/15/12 17

18 Anode to electronics matching PhotoDet - H. Grabas 6/15/12 18

19 Conclusion Successfully build a 3GHz 30 strip transmission anodes for fast timing detectors. More than 10dB of attenuation between strips. Similar principle can probably be used for fast SiPm. PhotoDet - H. Grabas 6/15/12 19