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.
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.