Draft specifications for a VME MCA and spectroscopy ADC

[Mark Rivers <RIVERS@cars3.uchicago.edu>]

    Folks,

I have drawn up the following draft specifcations for a VME multichannel
analyser and ADC which I would like to have built for use at the APS. I would
like to discuss this at the Feb. 23 meeting, and hope to get some feedback
before then. 

I have begun preliminary discussions with a vendor who might be interested in
building a VME MCA system. Are there other CATs who would be willing to help
underwrite the development costs?

                                   Mark Rivers

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Draft Specifications for VME Multichannel Analyser System for use at the APS
                                 Mark Rivers
                              January 27, 1995


The following are draft specification for a VME based MCA.  The system is
assumed to consist of two modules: an MCA module with memory and timing control
and an ADC module. Each MCA module could support at least 4 ADC modules.


                        Multichannel Analyser Module

24 bit input from ADC
    This allows:
        2-D operation with 2 12 bit ADCs
        Operation with 14 bit ADC and 10 tag bits

Acquisition modes
    List mode - Store input value current channel location; increment channel
                counter. This is used for 'event-mode' data acquisition and
                SVA sampling mode on ADCs
    Add 1     - Add 1 to channel referenced by input value. This is
                conventional MCA histogramming
    Add N     - Add input value to current channel location; increment channel
                counter. This is used with multichannel scalers.

Timing modes
    Preset real time 
    Preset live time
    Preset total counts in a range of channels.  
    Preset real time and live time range 1 msec - 10^6 seconds,
        accurate to 10 usec or 0.01%.
    In preset total mode, acquisition stops within 10 msec of reaching 
        preset total counts

Elapsed live time and real time available, accurate to within 10 usec or 0.01%.

32 data bits per channel (>4 billion counts/channel)

Minimum 1 MHz histogramming rate

Minimum of 1M channels (4 MB) capacity on board. Up to 16M channels with
companion memory boards.

Dual-ported memory with DMA to VME host

Capable of simultaneous operation from at least 4 ADCs. Common timing control
is acceptable.

Front panel indicators
    Acquire - LED indicating that the module is enabled to acquire data
    Active  - LED indicating that data is being acquired from an ADC input


                                     ADC

< 1 usec conversion time

13 bit (8192 channel) resolution

Input range 0 to +8V

Differential non-linearity: < +-1%

Integral non-linearity: < +-0.025%

Peak detect: 
    Automatic or delayed
    Delay time programmable from 0.5 to 100 usec

Collection modes
    Pulse height analysis (PHA) - Conversion on peak detect
    Sampled voltage analysis (SVA) - Conversion on GATE pulse

Input signals
    Input:  Analog input, range 0 to +8V
    Gate:   TTL signal used for gating and coincidence

Programmable gain from 256, 512, 1024, 2048, 4096 channels full scale

Programmable lower-level discriminator (LLD), 12 bit resolution, 
        range 0V to +8V
    
Programmable upper-level discriminator (ULD), 12 bit resolution, 
        range 0V to +8V

Programmable coincidence modes: 
    Coincidence: High input on Gate or no input on Gate
    Anticoincidence: Low input on Gate

The LLD and ULD are active during both PHA and SVA modes

Programmable zero offset voltage, 12 bit resolution, range +- 0.25V

Output signals:
    Acquire:  TTL level indicating that acquisition is enabled
    Event:    TTL pulse indicating that a conversion is complete
    Data:     A/D output on private 24 bit address bus to MCA board

Front panel indicators:
    % dead time:  LED bar graph
    Active:       LED indicating conversion in progress

Compatible with use with an analog multiplexor rather than direct amplifier
output. The analog multiplexor would present the voltage to the ADC input, and
manipulate the high order data bit to the MCA to indicate which amplifier a
pulse came from.