43
The Model 3377 time digitizer consists of 7 major subsystems:
TIME MEASUREMENTS
Four LeCroy MTD133 custom monolithic integrated circuits perform the
actual time measurements. The 250 MHz clock is provided by a crystal
oscillator, and a symmetrizing circuit which adjusts the duty factor to
50%. The MTD133 uses a synchronous counter which counts on both
clock edges, giving an effective counting rate of 500 MHz. A four stage
delay line interpolator divides the counting period into 500 picosecond
intervals. A phase locked loop using an external op amp in the feedback
circuit adjusts the delay line to be exactly 2 nsec long. When an input
occurs, the grey coded counter and interpolator are latched and stored
in the LIFO.
Each MTD133 contains 8 input channels, each with 16 words of LIFO
storage. Both the depth of the storage, and the maximum time range are
programmable. The data is stored in the LIFO in a grey code format.
When the data is read out, the grey code is converted to binary, the
Common hit time is subtracted, and the time difference is compared to
the maximum time. This is done in a 3 stage pipeline to increase the
readout speed. The readout is in channel order, and then reverse time
order., the most recent hit in a channel is read first. When the channel is
empty, or a hit with a time greater than the programmed maximum is
encountered, the readout proceeds to the next channel.
CONTROL AND READOUT
At the beginning of acquisition mode, the programmed values for hit
depth and time range are loaded into the MTD133s. At the end of
acquisition, when a Common Stop, or a Common Start Time Out is
received, the inputs are disabled, and readout begins. Three priming
pulses are required to fill the internal pipelines in the MTD133s, then
THEORY OF OPERATION
