Agilent Technologies DC122 Benutzerhandbuch

A full internal calibration of a digitizer can be very time consuming (> 100 s/digitizer), in particular for the HZ 
models. Therefore, several other options are available. They are documented in the Programmer's Reference 
Manual. A program can always be started with the digitizer in an uncalibrated state and data taken can be used for 
many kinds of testing. However, as soon as good data respecting the specifications of the instrument is required a 
calibration of at least the current acquisition state is needed. The full internal calibration has the advantage that it 
generates the calibration constants needed for any possible configuration of the instrument; its disadvantage is the 
time taken. If a more selective calibration is done it will allow the generation of good data in the current acquisition 
state. This calibration will remain useable whenever that acquisition state is used again for as long as the temperature 
of the instrument does not change significantly. A fast calibration of a channel in a configuration can be done in 
around a second. Many applications can save time by only performing calibration for the configurations that will 
actually be used. 

An application program will close devices if it exits normally. When a 10-bit digitizer is closed in this way its power 
consumption will be reduced. This has the consequence that if another application program is started later an 
appropriate warm-up period may have to be respected before a calibration is called for and full performance 
expected.  

The digitizers may be used in applications that require many data acquisition channels. In such cases it is possible to 
use more than one digitizer in a standard CompactPCI/PXI crate. Each DC Series 10-bit digitizer includes ASBus

2

, a 

proprietary high bandwidth auto-synchronous bus system that allows multiple digitizers to work together 
synchronously.  

ASBus

2

 distributes both the clock and trigger signals along a plug-in front panel bus, between all the digitizers that 

participate in the system. It allows any digitizer to act as the trigger source and any other digitizer to act as the clock 
source (acquisition master), enabling all the digitizers to be clocked at the same time. Synchronizing the clock signals 
between the devices improves the accuracy of cross-channel measurements and is essential for accurate time 
correlation between signals on different channels. 

ASBus

2

 is intended to connect modules of the same type, i.e. of the same model number, although some exceptions 

to this rule might be possible. If modules with the same model number, but different memory length options, are 
connected only the shortest memory length can be used. 

The ASBus

2

 connector is located on the front panel of each module. Bridges are used to connect adjacent modules 

for synchronization. An ASBus

2

 

multi-instrument is activated through software by a function call. Up to 5 6U 

modules, or 3 3U modules, may be synchronized with the ASBus

2

. More detailed information and the commands 

required to set up the ASBus

2

 clock and trigger distribution are included in the Programmer's Guide and Reference 

manuals. 

 

MMCX CLK IN 

50 Ω External Reference or External Clock Input 

MMCX I/O A 

User configurable (see below)  

MMCX TR OUT 

Signal occurs after an accepted TRIGGER.  

MMCX I/O B 

User configurable (see below) 

The I/O A and I/O B signals are 3.3 V compatible CMOS. This means that, on input, low is < 0.7 V and high must be 
in the range [1.7 V, 5.0 V]. An unconnected signal will be high. This definition ensures TTL compatibility. On 
output, the low level 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. 

 

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 MMCX connector. The pulse ends when the data 
acquisition for the trigger in question is complete.