Speaker
Description
Summary
The LHCb Muon Detector will contain 120 thousands physical
channels, corresponding
to Front-End (FE) Electronics input, and 26,000 logical
channels used for
triggering purposes and off-line muon identification. Each
physical channel
consists of an independent Amplifier-Shaper-Discriminator
(ASD) circuit. A single
FE board consists of two 8-channel ASD chip called CARIOCA
and one mainly digital
chip called DIALOG. In front of each channel connected to
the chamber output, there
are spark protection and chamber-to-FEB connection circuits.
A method to test
physical channels operation is important to avoid
inefficiencies due to failures on
detector read-out region: chambers strip/pad lines, physical
connections, FE
circuitry functionality, among others.
LHCb Muon System has foreseen 20 geometrically different
MWPCs. Depending on its
type, chamber capacitance can vary from roughly 40pF to
250pF and signal can be
read from anode and/or cathode connections. Due to the
later requirement, CARIOCA
has been developed to process both polarities by
implementing 2 different pre-
amplifiers at the very ASD input stage. They show slightly
different signal
responses depending on the chosen polarity operation. The
on-detector circuitry is
composed of three building blocks: OR-PAD, Spark-Protection
(SPB) and CARDIAC
(CARIOCA and DIALOG Circuitry). The first two boards make
use of passive components
while the third board processes and digitalizes chamber
signals. Those are some
considerations covered by the method used to evaluate
such chambers.
The test apparatus presented in this document has been
developed to evaluate the
front-end and chamber conditions before assembling it to
the detector. Diagnostics
are given based on FE output lines response, noise rate
versus threshold analysis
and evaluation of noise rate given reasonable threshold
values. To test output
lines functionality, FE auto-injection fixture is used to
generate signals on the
circuit input; control of their responses is done by means of
external counters.
With noise rate versus threshold analysis, considering a
Gaussian noise presence in
a discriminator input and a Gaussian time response
distribution, it is possible to
obtain information about three fundamentals characteristics:
the circuit bandwidth,
offset and its equivalent noise. Once such characteristics are
known, it is
possible to estimate other parameters as: chamber
capacitance, FE equivalent noise
charge and sensitivity. Finally, operational threshold
efficiency can be evaluated
by considering the relationship between threshold, in charge
(fC), and noise rate.
It will be presented results obtained during chamber tests.
To carry out such test and diagnostic procedures it has been
used two VME modules,
one used as external counters and another as interface VME-
USB, together with the
official LHCb Muon FE control electronics and a CANopen-USB
board plus a C++ and
Root integrated software, resulting in a fixture able to
perform FE control, data
acquisition and analysis. Additionally a barcode scheme has
been implemented
permitting identification of chambers and FE boards.
