PRELIMINARY
Document type: Title: Revision date: Revision:
User's Manual (MUT) Mod. V1729 4 Channel 12 Bit Sampling ADC 22/06/2005 3
NPO: Filename: Number of pages: Page:
00109/04:V1729.MUTx/03 V1729_REV3.DOC 38 16
3. Synchronizations and calibrations
3.1 Synchronization between the channels
3.1.1 Channels from the same board
A single trigger signal is used for all of the channels from the same board. The
acquisition of these channels will therefore naturally be synchronous, with a typical jitter
of only 20ps RMS. The possible temporal offset dT0, constant, between the channels
(principally due to the propagation of the trigger signal on the board, but also to the
different lengths of cables at the inputs) will be calibrated once for all. This calibration is
executed by sending a same signal on all of the inputs and by looking for the fine position
of the trigger on each of the channels.
In the case where the board is triggered on one of the input signals, a fine
synchronisation method consists of interpolating by software the crossing of the signal
through the trigger threshold on the given channel, this permitting the fine datation of all
the measured channels.
3.1.2 Channels situated on different boards
The synchronization is only possible if the trigger source is common to the different
boards. For this, several possibilities can be envisaged :
- to use an external trigger signal common to all of the boards.
- to generate the trigger signal on a fixed board (master) which triggers itself and to send
its TRIG_OUT signal output to the external trigger input of the other boards (via a NIM
buffer if there is more than one target board).
- to generate the trigger signal on any one of the boards. The TRIG_OUT outputs of all of
the boards will then be connected on an external NIM logic then the result will be
redistributed in a synchronous fashion to all the boards via their EXT_TRIG input. It is
this latter input which will then be programmed as the source of the asynchronous trigger
via the bit 4 of the TRIGGER_TYPE register on all the boards.
In all cases a calibration of the temporal offset between the boards is necessary. This
calibration, similar to that which is necessary to align the channels from the same board,
will be dependent upon the set-up (length of the cables…).
3.2 SYNC_OUT and BUSY signals
One of the NIM outputs of the front panel can be configured either as a SYNC_OUT, or
as a BUSY respectively with the help of the S4 and S2 straps. SYNC_OUT is a
synchronization signal corresponding to the writing in the first cell of the second column
of the circular analog memory, and which can be made available on the front panel. For
certain applications, this signal can permit triggering of the source analog signals and
thus guaranties their fixed position in the memory. Thus, if the temporal occupation of the
signals to acquire is low, the user will have the possibility to only re-read the beginning of
the depth of the analog memory and to thus limit the dead time linked to the acquisition.
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