The Timepix Chip
The Timepix Chip was derived directly from the Medipix2 development. It shares many of the physical dimensions of the Medipix2 chip but has a different functionality at the level of the single pixel. The chip was designed at the request of the EUDet Collaboration. Here is a summary of its properties:
- The square pixel size of 55 µm side length makes the Tmepix chip competitive with most of the existing imaging devices in terms of spatial resolution.
- Direct X-ray conversion in a semiconductor sensor minimises image blurring and avoids an extra conversion stage from X-rays into visible light.
- The chip is designed to accept either positive or negative charge input in order not to restrict the choice of the sensor material (Si, GaAs, CdZnTe,...). Detector leakage current gets compensated pixelwise at the input.
- The chip can also be combined with a Gas Gain Grid to read out electron deposition in a gas detector.
- Timepix has a single energy threshold. The threshold can be adjusted pixelwise with 4 bits for uniform performance of the whole pixel matrix.
- Each pixel can be programmed to work on one of 3 modes: Single particle counting, Time over Threshold or Arrival time mode. In the case of ToT or Arrival time mode the clock ticks are counted.
- Exposure times can be chosen arbitrarily. Data is accumulated in a 13-bit counter per pixel. The pixel overflows at 11810 counts. In single particle counting mode each pixel can handle count rates of about 100 kHz of randomly arriving particles. Read-out is performed after exposure to avoid dead time.
- Parallel and serial read-out are realised.
- The Timepix chip has an active area of about 2 cm². 256 x 256 pixels form the pixel matrix.
- Larger area coverage is a big concern of the collaboration. Timepix will therefore be 3-side buttable.