Mary K. Heintz

A new time-to-digital converter for the central tracker of the colliding detector at Fermilab

We describe a FPGA-based, 96-channel, time-to-digital converter (TDC) intended for use with the central outer tracker (COT) in the CDF experiment at the Fermilab Tevatron. The COT system is digitized and read out by 315 TDC cards, each serving 96 wires of the chamber. The TDC, which is implemented as a 9U VME card, has been built around two Altera Stratix FPGAs. The special capabilities of this device are the availability of 840 MHZ LVDS inputs, multiple phase locked clock modules, and abundant memory. The TDC system would operate with an input resolution of 1.2 ns, a minimum input pulse width of 4.8 ns and a minimum separation of 4.8 ns between pulses. Each wire input can accept up to 7 hits per collision. Memory pipelines are included for each channel to allow deadtimeless operation in the first-level trigger; the pipeline has a depth of 5.5 /spl mu/s to allow the data to pass into one of four separate level-two buffers for readout. If the level-two buffer is accepted, the data are passed through a processor implemented in the FPGA to encode the relative time-to-digital values by using the memory positions and addresses of the transitions due to the input pulses. This processing and moving of the data takes 12 microseconds; the results are then loaded into an output VME memory. A separate memory contains the resulting word count, which is used in performing a VME 64-bit chain block transfer of an entire sixteen-card crate. The TDC must also produce prompt trigger flags for a tracking trigger processor called the extremely fast tracker (XFT). This separate path uses the same input data but passes the stream through a special processor, also implemented in the FPGA, to develop the trigger data delivered with a 22 ns clock to the XFT through a high-speed transmission cable assembly. The full TDC design and multi-card test results will be described.

A design for large-area fast photo-detectors with transmission-line readout and waveform sampling

We present a preliminary design and the results of simulation for a photo-detector module to be used in applications requiring the coverage of areas of many square meters with time resolutions less than 10 picoseconds and position resolutions of less than a millimeter for charged particles. The source of light is Cherenkov light in a radiator/window; the amplification is provided by panels of micro-pores functionalized to act as microchannel plates (MCPs). The good time and position resolution stems from the use of an array of parallel 50 Ω transmission lines (strips) as the collecting anodes. The anode strips feed multi-GS/sec sampling chips which digitize the pulse waveform at each end of the strip, allowing a measurement of the time from the average of the two ends, and a 2-dimensional position measurement from the difference of times on a strip, and, in the orthogonal direction, the strip number, or a centroid of the charges deposited on adjacent strips. The module design is constructed so that large areas can be ‘tiled’ by an array of modules

Development of a 20 GS/s sampler chip in 130nm CMOS technology

In the scope of time of flight measurements at the scale of a few pico-seconds, a CMOS fast sampler chip is being developed in 130nm CMOS technology. It includes a 10-20GS/s timing generator lockable on a 40-80 MHz clock and four channels of 250 sampling cells able to record up to of 25 ns of analog information. Each sampling cell is integrated with a comparator allowing a 12-bit analog to digital conversion. The design and preliminary tests results are presented.

Position Measurements with Micro-Channel Plates and Transmission lines using Pico-second Timing and Waveform Analysis

The anodes of Micro-Channel Plate devices are coupled to fast transmission lines in order to reduce the number of electronics readout channels, and can provide two-dimension position measurements using two-ends delay timing. Tests with a laser and digital waveform analysis show that resolutions of a few hundreds of microns along the transmission line can be reached taking advantage of a few pico-second timing estimation. This technique is planned to be used in Micro-channel Plate devices integrating the transmission lines as anodes.