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60 4. ASIC performance - Electrical tests on bumped CIX 0.2 modules N o is e [A ] 1 n 1 0 0 p 1 0 p 1 p �� 1 0 0 f 1 0 0 f 1 p 1 0 p 1 0 0 p 1 n 1 0 n 1 0 0 n In p u t c u r r e n t [A ] (a) S N R 1 0 0 k 1 0 k 1 k 1 0 0 1 0 1 0 0 m 1 0 m 1 � � � �� 1 m 1 0 0 f 1 p 1 0 p 1 0 0 p 1 n 1 0 n 1 0 0 n In p u t c u r r e n t [A ] Fig. 4.15: Average integrator noise (a) and SNR (b) as a function of the input current with an additional IntBiasI current. The figure shows results from an unbiased 1 mm thick CdTe module. The bias current of 800 pA is used to guarantee a certain number of pump events per frame, thus allowing the measurement of very small input currents. Solid lines indicate the Poisson limit. An example of the typical noise amplitudes and signal-to-noise ratios (SNR) with and without bias current at 1 nA input current is given in Tab. 4.3. The table also contains the simulated quantum noise for an average photon energy of 30 keV. At the end of this section Fig. 4.16 gives an overview of the different factors, which influence the noise measurement. The figure shows the SNR as a function of the input current using the example of a 3 mm thick CdZnTe module. It is found that the best noise performance is achieved with unbumped, bare chips. The addition of an unbiased sensor generally increases the noise by a factor of 2 to 10. At high input currents the difference 1 0 0 0 0 0 S N R 1 0 0 0 0 1 0 0 0 1 0 0 � � � (b) 1 0 �� 1 �� 1 0 p 1 0 0 p 1 n 1 0 n 1 0 0 n In p u t c u r r e n t [A ] Fig. 4.16: Signal-to-noise ratio (SNR) for different input currents measured on a bare module (a-c) as well as one with an unbiased 1 mm thick CdTe sensor (d,e). The plot shows data taken in march 2007 (a) [1] as well as measurements taken at different CKInt integrator clock settings (10 MHz (b) and 20 MHz (c)). The lowest SNRs were measured in the bumped CdTe modules at fast clock settings and with an additional bias current (e).
4.4. Noise 61 No IntBiasI IntBiasI Quantum noise Frame [µs] Noise [pA] SNR Noise [pA] SNR Noise [pA] SNR 50 27 37 25 40 149 7 100 13 77 12 83 103 10 200 6.5 154 6 167 74 14 3000 0.6 1667 0.9 1111 18 56 Tab. 4.3: Integrator noise and signal-to-noise ratio at 1 nA input current, 2.6 fC integrator charge pump size and 10 MHz CKInt without and with 800 pA IntBiasI current. The last two columns contain the simulated quantum noise for an X-ray spectrum with an average photon energy of 30 keV. in noise between the bare chip and the one with a sensor attached is reduced. Finally, the influence of the integrator clock frequency on the SNR can also be identified in the measurements. The data show a significant reduction of the SNR when going from the regular CKInt clock setting of 10 MHz up to a frequency of 20 MHz.
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. . UNIVERSIT AT BONN Physikalische
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Contents 1. Introduction . . . . .
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B. CIX 0.2 readout . . . . . . . .
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2 1. Introduction This work is stru
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4 2. X-ray imaging 2.1.1 Photoelect
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6 2. X-ray imaging described by the
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8 2. X-ray imaging (a) Fig. 2.5: (a
Page 18 and 19: 10 2. X-ray imaging electrons back
Page 20 and 21: 12 2. X-ray imaging and were used i
Page 22 and 23: 14 2. X-ray imaging component and a
Page 24 and 25: 16 2. X-ray imaging a) c) b) d) Fig
Page 26 and 27: 18 2. X-ray imaging a) b) Pt CdTe:C
Page 28 and 29: 20 2. X-ray imaging the following d
Page 30 and 31: 22 2. X-ray imaging sensors [45]. L
Page 32 and 33: 24 2. X-ray imaging C o u n ts [a .
Page 34 and 35: 26 3. CIX 0.2 detector CIX 0.1. For
Page 36 and 37: 28 3. CIX 0.2 detector 3.3 CIX 0.2
Page 38 and 39: 30 3. CIX 0.2 detector distributed
Page 40 and 41: 32 3. CIX 0.2 detector Equally the
Page 42 and 43: 34 3. CIX 0.2 detector flowing into
Page 44 and 45: 36 3. CIX 0.2 detector closed and s
Page 46 and 47: 38 3. CIX 0.2 detector O ffs e t c
Page 48 and 49: 40 3. CIX 0.2 detector a) 0um 1000u
Page 50 and 51: 42 3. CIX 0.2 detector Alternativel
Page 52 and 53: 44 3. CIX 0.2 detector • Dual cha
Page 54 and 55: 46 4. ASIC performance - Electrical
Page 72 and 73: 64 5. CIX X-ray test setup • Anod
Page 74 and 75: 66 5. CIX X-ray test setup
Page 76 and 77: 68 6. Sensor material characterizat
Page 102 and 103: 94 7. CIX module performance under
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110 7. CIX module performance under
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112 7. CIX module performance under
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114 8. X-ray images images were tak
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116 8. X-ray images a) Average ener
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118 8. X-ray images By placing a di
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120 8. X-ray images C o n tr a s t
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122 8. X-ray images
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124 9. Conclusion and outlook • S
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126 9. Conclusion and outlook princ
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A. Differential current logic The d
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B. CIX 0.2 readout The readout sche
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C. Threshold scans and tuning A thr
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Bibliography [1] E. Kraft, Counting
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Bibliography 137 [32] A. E. Bolotni
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Acknowledgements Looking back at my
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UNIVERSIT . . AT BONN Physikalisches Institut - Prof. Dr. Norbert ...

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