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The LeCroy CAMAC Model 2277/EXP and 2277/EXP2 Hit Expanders are companion modules to the CAMAC Models 2277 and 3377, as well as the FASTBUS Models 1876 and 1877 Time Digitizers. When used with either expander, these TDCs experience an improved double pulse resolution (to 5 nsec for the 2277/EXP and 2 nsec for the 2277/EXP2) and the pipelined hit depth is increased to at least 64 hits per input. This is accomplished by routing one input signal to several channels, creating a single TDC channel with improved performance.

The EXPs can also be used in a stand-alone mode as a prescaler or a rate reducer with a divide by 4 or 8. The EXP module is basically an 8-channel divide by 4 circuit, with differential ECL inputs and outputs. It adds one more layer of flip-flops, dividing the rate in each channel by 8.

When one 2277/EXP is used with the 4434 ECL Scaler, the combination becomes an 8-channel 80 MHz scaler with a double hit resolution of 5 nsec instantaneous and 12.5 nsec sustained. In this configuration, all input pulses are counted. If used as a prescaler (i.e., every four hits provide only one output), then up to four EXPs can be used with a single 4434 for a total of 32 channels.



When used with the 1876 or 2277 TDCs, the 2277/EXP has two operating modes controlled by a single jumper on the front panel connector. The 2277/EXP2 has only one mode of operation.

Mode 1

With the jumper in place, the combined modules are an 8 input, leading edge only, 1 nsec resolution TDC. The TDC must be set to record leading edges only. The leading edges of 4 successive input pulses are routed to the 4 channels in the order 0, 3, 1, 2 (with a random starting phase).

Mode 2

With the jumper removed (mode 2), the pair of modules becomes a 4 input, leading edge and trailing edge TDC (for each group of 32 channels). As above, the TDC is set for leading edge recording. Leading edges are routed to the lower 4 channels of each 8-channel grouping; trailing edges are routed in the higher 4 channels. Each edge of the input pulse now has a double hit resolution of 5 nsec and 64 hit capacity.

Operating Conditions

The maximum input pulse rate is 200 MHz. The pulses arriving at the TDC have a minimum width of 10 nsec, and a minimum leading edge separation of 20 nsec, both well within the capabilities of the either the 1876, 1877, 2277 or 3377. The combined units will correctly record leading edges only 5 nsec apart, and can record up to 64 leading edges per "channel".

The minimum pulse width is limited by the performance of the ECL flip-flops, and not by the TDC, since the 2 edges are routed to different TDC channels. This composite "channel" will properly record both edges of a 200 MHz square wave (5 nsec period, 2.5 nsec pulse).

The EXP2

The 2277/EXP2 is similar to mode 2 described above except that the combination TDC and expander expands 32 channels of the 1876, 1877, 2277 or 3377 to 2 inputs, 256 edges per channel TDC with both edges recorded. The same edge double hit resolution is 2 nsec, and the minimum width is 1 nsec. The 2277/EXP2 uses a faster logic family to achieve the higher speed. Front panel lemo connectors accept NIM level inputs as narrow as 1 nsec. ECL inputs are also available. Leading edges are routed to the lower 8 channels of each 16-channel gouping; trailing edges are routed to the higher 8 channels.

Operating Conditions

The 2277/EXP2 maximum input pulse rate is greater than 450 MHz, typical 500 MHz. The same edge double hit resolution is 2 nsec, and the minimum width is 1 nsec. The EXP2s use another layer of flip-flops and a faster logic family to achieve the higher speed.

The 1877 and 3377 will properly record a long pulse train at the maximum rate. The 2277, 1176 and 1876 will record a short burst at the maximum rate, but the long term average rate must be less than 1/2 of the maximum rate.

Readout of TDCs

When the data is read from either TDC, there are 96 or 32 channel numbers, not 8, 4, or 2. The simplest way to deal with this is to mask the least significant bits of the channel number. For the EXP Mode 1, treat channels 0, 1, 2, 3 as channel 0. Mask 2 bits for the EXP, 3 bits for the EXP2. Sort all of the data for this new channel 0 into time order.

For the leading and trailing edge mode (EXP or EXP2) proceed as above, but the least significant bit of the new channel number is now the edge flag. For the first input of the EXP, the TDC channels 0-3 correspond to the leading edge and channels 4-7 correspond to the trailing edge. For the EXP2 channels 0-7 are the leading edge, channels 8-15 are the trailing edge.

CAMAC Control

These two modules use the CAMAC crate for power and mechanical support only. There are no CAMAC com mands required for operation. There is no clear; the modules are free running.

Specification Chart

Input and Output of the Model 2277/EXP

Copyright© September 1995. LeCroy is a registered trademark of LeCroy Corporation. All rights reserved. Information in this publicaction supersedes all earlier versions.