REPTile Electronics Design
The REPTile electronics system acts to process and interpret the signals coming from the instrument detectors and to calculate electron and proton count rates in each of the four energy channels. A block diagram of the signal chain below shows the stages the signal passes through before count rates are calculated. The chain is duplicated for each of the four detectors.
- When a particle hits a detector it produces a shower of electrons in the silicon, creating a charge pulse, which is collected on the anode.
- The Charge Sensitive Amplifier (CSA) acts to amplify the signal and convert it to a shaped voltage pulse.
- The Pulse Shaping Amplifier (PSA) amplifies the signal by 3.4x and further shapes it.
- Voltages are passed into a three-stage discriminator chain, which is used to identify whether the particle is an electron or proton based on the voltage measured. Particles depositing between 0.25 and 1.5MeV in a detector (a discriminator output of 100) are classified as electrons, and those depositing > 4.5MeV (discriminator output 111) as protons.
- In the final signal processing stage, the Complex Programmable Logic Device (CPLD) interprets the discriminator values and classifies the particle by species and energy. 6-second count rates are calculated for each energy channel for both electrons and protons, and these rates are passed on to the Command and Data Handling (C&DH) system to be stored and transmitted down to the ground.
The REPTile electronics board is also responsible for providing the 350V bias across each detector and for containing housekeeping sensors to track temperatures, voltages, and currents of the system.