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SiPM Amplifier Optimization (view source)
Revision as of 05:12, 4 February 2009
, 05:12, 4 February 2009no edit summary
The SiPM amplifier currently in use for SiPM characterization ([http://www.photonique.ch/ Photonique] item "AMP_0604") must be adapted for tagger microscope use. The following is a brief outline of the design requirements. They are discussed in detail in the following sections
The SiPM amplifier currently in use for SiPM characterization ([http://www.photonique.ch/ Photonique] item "AMP_0604") must be adapted for tagger microscope use. The following is a brief outline of the design requirements. They are discussed in detail in the following sections
# adjustable gain, ranging from readout of hundreds of pixels to calibration with single-photon counting [#Gain]
# adjustable gain, ranging from readout of hundreds of pixels to calibration with single-photon counting
# less than 15% gain variability on transistor <math>\beta</math> (<math>h_{FE}</math>) parameter
# less than 15% gain variability on transistor <math>\beta</math> (<math>h_{FE}</math>) parameter
# summing circuit to pool SiPM signals in groups of 5 (readout of individual channels must not affect readout of the some regardless of termination used)
# summing circuit to pool SiPM signals in groups of 5 (readout of individual channels must not affect readout of the some regardless of termination used)
== Minimal Dependence on <math>\beta</math> ==
=== Minimal Dependence on <math>\beta</math> ===
Dependence of a design on a value β of a transistor is never a good idea, given its variability as a function of temperature. The value also varies between one transistor and the next. The high speed transistors necessary in this design are already at a disadvantage with respect to this design goal, due to their low beta with the result of greater significance of the parameter's variation. This issue will be discussed at length below.
Dependence of a design on a value β of a transistor is never a good idea, given its variability as a function of temperature. The value also varies between one transistor and the next. The high speed transistors necessary in this design are already at a disadvantage with respect to this design goal, due to their low beta with the result of greater significance of the parameter's variation. This issue will be discussed at length below.
== Summing Circuit ==
=== Summing Circuit ===
While the microscope contains 500 optical channels resulting from the two-dimensional segmentation of the focal plane, only the energy bin information is important. The vertical column of 5 scintillating fibers in the focal plane can then have its signals summed, reducing the count of channels requiring readout to 100. However, the design of the microscope calls for individual readout in 5 columns spread around the focal plane in order to retain the knowledge of the two-dimensional orientation of the electron stripe.
While the microscope contains 500 optical channels resulting from the two-dimensional segmentation of the focal plane, only the energy bin information is important. The vertical column of 5 scintillating fibers in the focal plane can then have its signals summed, reducing the count of channels requiring readout to 100. However, the design of the microscope calls for individual readout in 5 columns spread around the focal plane in order to retain the knowledge of the two-dimensional orientation of the electron stripe.
=== Short Pulses ===
The duration of the amplified signals is, in essence, the dead time of the channel. (Pulses with significant overlap are difficult to distinguish.) The lower bound of the pulse width is set by the scintillator. The BCF-20 intended for use in the microscope has a decay time of 2.7 ns. A somewhat stricter restriction is set by the sampling rate of the ADC - 250 MHz. A rough (and vague) guideline of 15 total signal duration has been observed during the design.
=== Power Consumption ===
Operation of over 500 such amplifiers (spares are available on each board) in a sealed box presents an issue of heat management. High temperatures inside the microscope should be avoided especially due to the sensitivity of SiPM parameters on temperature. Note also that the amplifiers will be packed very tightly (~5 mm strips) in the final layout. 30 mW has been set as the power budget per amplifier. The restriction on the summing circuit is not as critical, because there are 5 times fewer such circuits in the microscope. Contribution from the actual AC signals and various voltage regulators are negligible and are not taken into account.
== Design Implementation ==
However, care must be taken to avoid creating integrators (low-pass filters) in the amplifiers that may stretch the pulse significantly.
To maximize the possible running rate of the microscope, signals leaving the ampifier should be as fast as possible