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TIMEPIX Characterization with test pulses with the Syracuse test stand. Ryan Badman , M. Artuso, J. Wang, Z. Xing July 7 th , 2010. Uses photon counting approach 256x256 pixels (65,536 total) Each pixel is 55x55 microns Device consists of a semiconductor chip made of 300 microns-thick Si.
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TIMEPIX Characterization with test pulses with the Syracuse test stand Ryan Badman, M. Artuso, J. Wang, Z. Xing July 7th, 2010
Uses photon counting approach 256x256 pixels (65,536 total) Each pixel is 55x55 microns Device consists of a semiconductor chip made of 300 microns-thick Si. Each pixel is connected to a preamplifier, discriminator and digital counter integrated on the readout chip. The minimum detectable charge is about 650-750 electrons. Timepix Hybrid Pixel detector
The non-linear behavior near threshold produces offsets in the conversion between time-over-threshold and charge which make the pseudo-Landau (cluster TOT) most probable value dependent upon the number of pixel per cluster. (here put the 4 plots from zhou) It is important to determine the absolute value of the minimum detectable charge at any given threshold to have an accurate prediction of the sensor resolution (for this you can get a plot from JC) Motivation
Jianchun Wang ToTvs Injected Charge Measured by Atreyi, Paula et. al. Overall performance of all channels. = Q+offset Used in simulation of next slide, offset=1.2(0.9) for threshold =1.25(1.55)
Tests are controlled by the program Pixelman which allows for 4 modes of operation • 1.Medipix(Counter counts incoming particles) • 2.TOT (Counter is used as Wilkinson ADC allowing direct energy measurements in each pixel) • 3. Timepix (TOA) (Counter works as a timer and measures the time of the particle detection). • 4. Timepix 1-hit (Almost the same as 3) modes
Goal: determine the charge versus TOT calibration curve at different thresholds. An external clock, that can be set up to 80 MHz, increments the TOT counter continuously while the preamplifier output is above the threshold. Ours was set at 40MHz in agreement with the majority of data taking in the 2009 test beam. Same applies to the various biases. TOT Scan
First step: Threshold Equalization The mean equalization was checked each day and was consistently 494-495, with a standard deviation value about 3-4.
x = ta + y – b + sqrt[(b+ta-y)*(b+ta-y) + 4ac] /2a where x is the energy and y is TOT This is the function which we will use to derive the charge versus TOT conversion Using coefficients in inverse surrogate function
Fit formula is a*x + b –[ c / (x - t) ] Fit coefficients
The following graphs show that if you mask all but one pixels whiletaking data, the TOT value is lower per pixel than if you leave all pixels unmasked (spacing 4) during data acquisition. Systematic studies
Pixel 256,256, TH200 All Pixel = all unmasked (50 trials) Single Pixel = 1 unmasked (50 trials) Richards : Richards’ data, he left all pixels unmasked and only did one trial per pixel
Vertical Axis = (noise edge – THL) x 25 (electrons) • Horizontal Axis = TOT(at 0.5V) x 0.025microseconds, for each THL Charge vs tot graphs
Fires a test pulse of a given magnitude at a pixel for a specified range of TH levels. The y-axis is the mean value of each acquisition out of 100 trials. Medipix DAC scan The TH value for when the S-curve is at 50% of the noise-edge value tells for which TH value that the specified test pulse strength is the minimum test pulse magnitude needed for a signal.
Ne = Number of Electrons • Upper Line: Ne = 7.8e-15 [femto-Farads] x TP[V]/ 1.6e-19 [C] • Lower Line: Ne = (THL_noise-edge – THL_midpt) x 25. Dac calculations
DAC Data TP (mV)
Doing Richard’s method of taking data with all pixel’s unmasked produces higher TOT values per pixel than only leaving one pixel unmasked. … … … Conclusions
Also, thanks to A. Borgia, X. Llopart, and R. Plackett for getting the tp to work.
