Chapter 4 Arb Operation
DAQArb 5411 User Manual 4-18
©
National Instruments Corporation
Note: Marker output signals are an important feature to trigger other
instruments or devices at a specified time while a waveform generation is
in progress.
Analog Output
Figure 4-17 shows the essential blocks of analog waveform generation.
The 12-bit digital waveform data is fed to a high-speed DAC. A
low-pass filter filters the DAC output. This filtered signal is
pre-amplified before it goes to a 10 dB attenuator. The DAC output can
be fine-tuned for gain and offset. Since the offset is adjusted befo re the
main attenuators and amplifier, it is referred to as pre-attenuation
offset. This fine-tuning of gain and offset is done using separate DACs.
The output from the 10 dB attenuator is then fed to the main amplifier,
which can provide ±5 V levels into 50 Ω. An output relay can switch
between ground level and the main amplifier. The output of this relay is
fed to a series of passive attenuators. The output of the attenuators is fed
through a selectable output impedance of 50 or 75 Ω to the I/O
connector.
Figure 4-17. Analog Output and SYNC Out Block Diagram
Figure 4-18 shows the timing relationships of the trigger input,
waveform output, and marker output. Td1 is the pulse width on the
trigger signal. Td2 is the time delay from trigger to output on Arb
DAC
Gain
DAC
Pre Amp Main Amp
Filter
Low-Pass 10 db
Attenuator Attenuators
Output
Enable
25 ΩARB
Selector
50 Ω/75 Ω
Offset
DAC
12
Clock
Level
DAC
+
-
SYNC
Comparator
50 Ω
50 Ω
(63 dB in 1 dB steps)