Default Beetle Parameters

These are the recommended parameters for VELO operation. This is version v1.0 21st July 2008.

Register name Value (in hex) Value
itp 0x15 164 μA
ipre 0x4B 585 μA
isha 0x0A 80 μA
ibuf 0x0A 80 μA
vfp 0x0F 150 mV
vfs 0x33 500 mV
icomp 0x00 0 μA
ithdelta 0x00 0 μA
ithmain 0x00 0 μA
vrc 0x00 0 mV
ipipe 0x0D 102 μA
vd 0x82 1275 mV
vdcl 0x69 1030 mV
ivoltbuf 0x14 157 μA
isf 0x1A 200 μA
icurrbuf 0x66 796 μA
latency 0xA0 ?? (25ns)
roctrl 0x1C  
rclkdiv 0x00  
compctrl 0x0A  


The basic reference is the Beetle Reference Manual Table 14 gives the conversion factor for the register settings to parameter values.

The pulse shape related parameters were primarily determined from a study of ACDC 2 data by Kazu Akiba. Presentation of Pulse Shape Analysis

This working point was optimised around values from studies by Lars and Jan Beetle parameter studies

There is good detail on the variation with parameters in the Glasgow burn-in study of Franciole, but this does not include the 150mV Vfp working point Glasgow burn-in Analysis

First detailed analysis of Beetle pulse shapes from Juan Beetle 1.3 pulseshape

List of Beetle Parameter settings used at various places from Tony A. FNAL testbeam e-log

Notes on parameters

Itp - test pulse bias current

Ipre - some effect on pulse shape. sets the preamplifier bias current. Higher currents decrease the rise time and the remainder and increase the pulse undershoot. Increasing the value also increases the power consumption.

Isha - some effect on pulse shape. defines the shaper bias current. Increasing currents shift the DC-offset to lower values and results in a slightly decreasing rise time, remainder and undershoot.

Ibuf - sets the buffer bias current. It does not affect the shape of the pulse.

Vfp - significant effect on pulse shape. sets feedback preamplier resistance, regulates discharge of the pre-amplifier. Increasing Vfp reduces spillover but increases the undershoot. If Vfp is too high charge-up of the output node of the pre-amp at high rates could occur, at VELO occupancy a Vfp of 200mV is probably a little high.

Vfs - significant effect on pulse shape. sets feedback shaper resistance, sets interation time. Increasing Vfs increases the signal/noise but also increases the pulse rise and fall times.

Icomp, Ithdelta, Ithmain,Vrc - are all not used for the VELO. They are used for the comparator for binary output for the pile-up.

Ipipe - see p24 Beetle ref manual

Vd - determines the potential to which the pipeamp is reset. This depends on Isha and Ibuf, for which we have the default values, see p24 of Beetle manual.

Vdcl - see p24 Beetle ref manual

Ivotbuf - see p24 Beetle ref manual. Depends on Ipipe, for which we have the default.

Isf - multiplexer buffer bias current

Icurrbuf - some effect on pulse shape

Latency - depends on timing. We wish to sample 6ns after the peak of the pulse. This equalises the pre-spill and spill-over signals.

The values of the following parameters have been put at their Beetle manual defaults, although these are not the values that have been used during VELO testbeam, lab studies. Nobody knows where the (several different sets) of values that have been used in the testbeam, labs studies come from.

Vd, Vdcl, ivotbuf, Isf.

-- ChrisParkes - 14 Jul 2008

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Topic revision: r4 - 2008-08-08 - StefanoDeCapua
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