Many remote sensing instruments include the detection of photon/particle events, position decoding and time-of-hit measurement. Microchannel plates (MCPs) are widely used to detect photons and particles for position sensing and relative time of impact in imaging and time-of-flight (TOF) spectrometers. Two dimensional delay lines are used for fast and accurate readout of MCPs. Instruments that use these techniques are Neutral Atom Imagers and Particle Spectrometers to study planetary magnetospheres; photon counting detectors for spectrographic imaging in the far-UV and extreme-UV to study the earth's aurora and airglow; laser range finders. In all these there is a requirement of accurate and/or fast time interval measurement. An advance TOF system-on-a-chip has been developed that includes the complete signal processing electronics for MCP readout: two channels (start- stop) of amplifiers and constant fraction discriminators (CFDs), an 11-bit Time to Digital Converter (TDC), and control/readout logic. The TOF chip is capable for a time resolution of <50ps including time walk and time jitter, the dead time is as low as 0.5us; the power dissipation is a function of counting rate and time resolution-for resolution of similar to100ps the power is <20mW at rates <100K/sec and <50mW at rates <1M/sec. The TOF chip flies on the NASA/IMAGE spacecraft launched in 2000 and is part of many other science instruments such as particles and fields, and laser altimeter on MESSENGER.

A CMOS time-of-flight (TOF) system-on-a-chip (SoC) for precise time-interval measurement with low power and high rate has been developed. Microchannel plate electron multipliers or photomultiplier tubes (PMTS) typically produce the start-stop delta-Ts of radiation events to be processed. The TOF chip includes two constant fraction discriminators (CFDs) and a time-to-digital converter (TDC). The CFDs interface to start and stop anodes through two simple preamplifiers and perform the signal processing for time walk compensation. The TDC digitizes the time difference with reference to an off-chip precise oscillator. The design is full custom in both the analog and the digital sections. A first version of the TOF chip developed in a 0.8-mum CMOS process achieved CFD time walk of similar to350 ps for an input amplitude dynamic range of 40 db and a combined CFD+TDC time jitter of similar to180 ps. The total power dissipation was similar to20 mW at an event rate of 100 K/s and similar to30 mW at a rate of 1 Meg/s. This chip is part of the high-energy neutral atom instrument onboard the NASA/IMAGE spacecraft launched in March 2000. It is selected for many other instruments, including the particle sensor, the fast plasma sensor, and the laser altimeter of Messenger for the Mercury exploration to be launched in 2004.

A time-of-flight (TOF) system-on-a-chip (SoC) for precise time interval measurement at low power and high rate has been developed. A micro-channel plate (MCP) electron multiplier typically produces the start and stop of a radiation event to be processed. The TOF chip includes two Constant Fraction Discriminators (CFDs) and a Time to Digital Converter (TDC). The CFDs interface to start and stop anodes through two simple preamplifiers and perform the signal conditioning for time walk compensation. The TDC portion digitizes the time difference with reference to an external precise oscillator. A first version of the TOF chip developed in a 0.8 u CMOS process achieved /spl sim/350 ps total time resolution, including time walk and time jitter, with /spl sim/20 mW power consumption at a rate of /spl sim/100 K events/sec and /spl sim/30 mW @ 1Mevents/sec. This chip is part of the HENA instrument of the NASA/IMAGE mission launched in March 2000 and is baselined for many other missions including the Energetic Particle Sensor (EPS) of Messenger etc.

The authors have implemented a new commandable threshold PHA-accumulation unit for the MIMI/LEMMS particle detection instrument of the Cassini mission to Saturn. The implementation is based on two full custom VLS ASICs specifically designed, fabricated, and space qualified for this project. The present system overcomes common fine tuning pre-flight and in-flight calibration difficulties associated with conventional fixed threshold systems of past missions, while significantly reducing weight and power. A brief description of the design as well as experimental results are presented.