Authors: Simeonov, L.I.
Reference: Proc.of the 5th Nat.Conf. with Intern.Part. on Contemporary
Problems of Solar-Terrestrial Influences, Sofia, 73-75, 1998.
Abstract:
Presented are considerations for the design of the electronic
readout circuitry of the solid-state detector on the charge, energy and
mass analyzer STOF of CELIAS on SOHO. The silicon solid-state detector
is divided in 192 individual pixels in order to achieve noise reduction.
Each pixel is connected to a separate charge-sensitive amplifier
channel. The channels are grouped by 32 in monolithic chips, called
CAMEX32, an abbreviation of CMOS Multichannel Analog Multiplexer. The
outputs of all channels are connected to a shift register, which
provides the conditions of multiplexing to a single serial output. Every
amplifier chip is commanded by a digital steering circuitry,
monolithically integrated in a separate chip, called TIMEX. The steering
chips are time-adjusted by the information from the time-of-flight
measuring compartment of the sensor. The individual amplifier channel
consists of a well-known charge-sensitive amplifier and a sampling group
of four identical capacitors and its amplifier. When a solar energetic
particle hits an individual pixel of the solid-state detector, the pixel
acts as a charged capacitor at the input of the charge-sensitive
amplifier. The reduction of the noise, which has a complex nature, is
achieved by a time correlated sampling of the signal, performed by the
group of the four sampling capacitors. The ideal mode of operation
concerns a situation of synchronously coming to the solid-state detector
pixels particles, or in the case, for which the CAMEX chip was initially
created, i.e., in beam-collider experiments as a low-noise front-end
readout electronics for the vertex microstrip detectors. In this
experiments the events, or bunch crossings occur at predictable
instants, thus giving the possibility of secure signal processing. This
is not the case in registration of solar energetic particles, whose
unpredictable time arrival on the detector pixels could be called
asynchronous and implies a corresponding mode of operation of the
sampling capacitor group of the amplifier channel.