Agilent Technologies DP211 - Manual (Page 38)

User Manual: Family of 8-bit Digitizers Page 38 of 66
will be in the range [0 V, 0.7 V] and the high level in the range [1.7 V, 3.3 V] for HiZ. The high level output will
typically give 0.8 V into 50
Ω. The I/O A or B connectors can be used for an Enable trigger input or the following
output signals: 10 MHz reference clock, Acquisition skipping to next segment, Acquisition is active, Trigger is armed.
3.9. External Trigger Output (DP1400 & DC271-FAMILY)
When the digitizer is ready to be triggered and a valid trigger signal occurs, a trigger output is generated for external
use. It is always available on the Front Panel Trigger Out MCX or MMCX connector. The pulse ends when the data
acquisition for the trigger in question is complete.
NOTE: The External Trigger Output functionality is implemented in the hardware. No Trigger Out signal occurs for
software-generated triggers such as those of the AUTO mode of AcqirisLive or through the use of the function
AcqrsD1_forceTrigger. However, AcqrsD1_forceTriggerEx does generate the signal.
Trigger Output Block diagram:
The output swing is 1.6 V ( ± 0.8 V)
when unloaded and 0.8 V when
terminated on 50
Ω. The rise and fall
times are 2.5 ns typical. The offset can be adjusted, by software control in the range [–2.5 V, +2.5 V] unloaded, or [-
1.25 V, +1.25 V] into 50
Ω. The maximum output current
capability is ± 15 mA. As the output is retro-terminated, it is
possible to drive a 50 Ω line unterminated (HiZ) without loss of
performance.
Signal: 1.6V swing
0v centered
Offset: +/-2.5 V
G=1
50 Ohm
Trigger Out
For a TTL compatible signal, set the offset to 1.0 V and the
swing at destination will be +0.2 to +1.8 V.
For an ECL compatible signal, terminated on 50 Ω to –1.2 V,
set the offset to –1.2 V and the output will be in the range [–0.8
V, –1.6 V]).
Alternatively, to reduce the current drawn from the digitizer, the terminations shown here can be used:
For the DC135/DC140/DC211/DC211A/DC241/DC241A/DC271/DC271A/DC271AR modules, a standardized
trigger out signal can also be routed to the PXI Bus Star Trigger line.
3.10. Frequency Counter mode
The new DC140 and DC135 digitizers offer an optional Frequency Counter (FC) mode. This option allows the
measurement of the average frequency or period of a signal for frequencies up to 400 MHz over a user-selectable
aperture between 1 ms and 1000 s. The accuracy is limited by that of the timebase, < 2 ppm; the short term stability
is of ~ 0.1 ppm. The accuracy can be improved if an appropriate external reference clock is used. Frequencies in
excess of 100 MHz will be measured using the HF divide by four feature of the trigger circuit.
A digitizer with the FC option can also totalize the number of triggers during a chosen time interval or a user-
provided gate signal. This can be done for trigger frequencies under 125 MHz and for total counts up to 2
48 . The time
interval is measured using the same clock as is being used to drive the digitizer. The user gate signal has to be made
available on one of the Control I/O inputs.
R
68
R
220
-5V
GND
Trigger
Out
With
Offset
-1.18V
R
68
R
220
GND
+5V
ECL
Signal TTL
signal
Trigger Out
With
Offset
+1.18V