NMOS-based high gain amplifier for MAPS. Andrei Dorokhov Institut Pluridisciplinaire Hubert Curien (IPHC) Strasbourg, France. VI th INTERNATIONAL MEETING ON FRONT END ELECTRONICS FOR HIGH ENERGY, NUCLEAR, MEDICAL AND SPACE APPLICATIONS Perugia, Italy 17- 20 May 2006.
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Institut Pluridisciplinaire Hubert Curien (IPHC)
VI th INTERNATIONAL MEETING ON
FRONT END ELECTRONICS
FOR HIGH ENERGY, NUCLEAR, MEDICAL AND SPACE APPLICATIONS
17- 20 May 2006
e-mail address: Andrei.Dorokhov@IReS.in2p3.fr
slides are available at
Amplification is needed to decrease noise contribution from switching networks, like clamping or sampling.Amplifiers for MAPS
small signal Gain = Vout/Vin = gm1 /(gm2 +gmb2 +gds1 +gds2)
As an example from simulation to be presented later:
gm1=47 mS gm2=4 mS gmb2=0.9 mS gds1=8 nS gds2=0.5 mS
Due to gm2 there is unwanted dependency of Id on Uout , so
can we reduce dependency of Id on Uout without changing gm2 ?
-> decouple the gate of the load transistor from the power supply with one additional NMOS transistor, used as a diodeImproved load for the common source transistor
Gain = Vout/Vin = gm1 /(gm2 +gmb2 +gds1 +gds2)
The AC gain should increase, while the DC operational point should not change!
AC gain is 8dB larger!
gmb2 +gds1 +gds2 become significant and limit the amplification, and also the gate is not perfectly decoupled -> still some fraction of gm2 exist…
improved load with power on switch
low frequency-pass feedback
correlated double sampling circuit
common source transistor with power on switch
NWELL size is4.25 mm x 3.4 mm, pixel pitch size 30 mm x 30 mm,
pixel matrix: 4 columns x 15 rows
Single pixel amplitudes distribution, superimposed for all 60 pixels, no amplitude cut is applied
If gamma goes directly to the NWELL volume ( very small <<1% fraction of all gammas), all delivered charge will be collected by single pixel and this value used to determine conversion gain (mV/e) for the amplifiers
Each pixels is calibrated individually, example of calibration peak for pixel
Distribution of calibration peaks for all pixels
Noise amplitude distribution for each pixel is fit to Gaussian, and sigma is taken as noise value for each pixel of 60Tests with Fe55 source, noise
Noise value distribution for all pixels, average noise is about 7.5 e or 540 mV at the column output
Seed pixel amplitude distribution for all pixels, the most probable value for the collected charge in the seed pixel is about 300 e, or 18 % of total charge
Charge collection in 3x3 pixels cluster, the most probable value for the collected charge is about 950 e, or 58% of total charge
Events selection: same as for the seed amplitude distribution
This development work would not be possible without support of many people from CMOS sensors group at IPHC:
W. Dulinski and M. Winter – for encouraging me to improve the amplifier for MAPS and for the fruitful discussions, special thanks to W. Dulinski for making the layout for my four different amplifier designs of which actually only two worked (well…)
CAD specialists - C. Colledani, F. Guilloux, S. Heini, A. Himmi, Ch. Hu,
O. Robert, I. Valin, for their help with Cadence,
Data acquisition, test and measurementsspecialists - G. Claus,M. Goffe, K. Jaaskelainen and M. Szelezniak for providing me test setup and acquisition software