TDC-GPX acam messelectronic gmbh, TDC-GPX Datasheet - Page 47

• Manufacturer Part Number: TDC-GPX
• Description: Precision Time Interval Measurement
• Manufacturer: acam messelectronic gmbh

Parameter
5.3 M-Mode Basics
Alutrigger
M-Mode is activated by setting MSet = 31 (Reg3) and
Mon = 1 (Reg4).
The M-Mode for maximum resolution is basically an
extension of the R-Mode. The block diagram and the
input circuitry are the same as in R-Mode. Also the
furhter settings are the same as in R-Mode.
In this mode the TDC-GPX accepts only one Stop per
channel. It is necessary to select M-Mode in combina-
tion with quiet mode.
Input circuitry
In M-Mode the TDC-GPX has differential low-voltage
PECL input buffers. The power for the differential in-
puts has to be switched on separately by setting regis-
ter 6, PowerOnECL = ‘1’.
The detailed input structure is shown in Figure 29.
Each input can be set to be sensitive to rising or falling
edge. This is done in register0, RiseEn0..2 and
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Start
Maximum resolution:
2 stop-channels referring to 1 start channel
1 Hit per channel
0 ns to 40 µs measuring range
Quiet mode
LVPECL inputs
Max. 500 kHz continuous rate per channel
Max. 1 MHz continuous rate per chip
Stop
Standard deviation down to 10 ps,
Peak-peak down to 70 ps
acam-messelectronic gmbh - Am Hasenbiel 27 - D-76297 Stutensee-Blankenloch - Germany - www.acam.de
Figure 35: Measurement timings
Time (Condition)
400 ns (min)
1.5 ns (min.)
3.2 ns (min.)
40 µs (max.)
1 µs (max.)
0 ns (min)
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Minimum pulse width
Minimum pulse width
Start to Stop
Stop to ALU trigger
ALU trigger to data valid
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Description
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FallEn0..2. A zero in both bits for one channel at the
same time disables the channel.
All inputs can be disabled by hardware, the stop inputs
separately for rising and falling edges (pin ‘StopDis1’
disables inputs DStop1,rising edge etc.).
They also can be disabled by software setting the ‘Dis-
able’ in register 2. The ‘Disable’ bits have to be set in
triples, e.g Disable3, Disable4 and Disable5 to disable
DStop1.
StopDisStart & StartDisStop
By default the Start and Stop inputs of the TDC-GPX
are open immediately after a reset.
The consequence for the Stop channels is that even
hits coming before a Start pulse will be measured. The
bit StopDisStart in register 5 disables the Stop chan-
nels until there is a Start pulse. A consequence is that
there is a minimum delay of 7 ns after the Start before
hits are accepted on the Stop channels.
With single-start only the first Start pulse is used for
the measurement. In case more than one Start pulse
is expected this might cause an overflow of the Hit
FIFO of the Start channel. This will produce garbage
data. There we recommend setting the StartDisStart
bit in register 5. A ‘1’ disables the Start channel after
the first Start pulse.
Start-Offset
For several reasons a programmable offset is added
to the stop time. One reason is to compensate for
different internal delays from the input buffers to the
TDC unit in the Start and Stop paths. It allows handling
Start-Stop intervals down to 0 and even less. The off-
set value ‘StartOff1’ is set in register 5 in multiples of
the I-Mode BIN and 18 bits wide. Internally the start
offset is added to the time measurement result and
has to be subtracted from the value read from the
TDC.
Adjusting the Start-Offset
The Start-Offset register of the TDC-GPX allows the
compensation for the offset due to the different inter-
nal delays. It allows to do measurements down to 0 ns
time intervals between Start and Stop. The correct
setting should be done by experiment.
Procedure for single start applications:
1. Set StartOff1 = 0
TDC-GPX