National Instruments NI 5401 用户手册

Chapter 2

Function Generator Operation

©

 National Instruments Corporation

2-7

After a start trigger is received, the waveform defined by the first stage is 
generated. Then, the device waits for the next trigger signal. On the next 
trigger, the waveform described by the second stage is generated, and so on. 
Once the staging list is exhausted, the waveform generation returns to the 
first stage and continues in a cyclic fashion.

Figure 2-7 illustrates a stepped trigger mode of operation. Switching from 
stage to stage is phase continuous. In this mode, the time instruction is not 
used. The trigger paces the waveform generation from one frequency to the 
other.

Figure 2-7.  Stepped Trigger Mode

Analog waveforms are generated as follows:

1. The 12-bit digital waveform data is fed to a high-speed DAC. 

2. A lowpass filter filters the DAC output. 

3. This filtered signal is 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 

before the main attenuators and amplifier, it is referred to as pre-attenuation offset. This 
fine-tuning of gain and offset is performed by separate DACs.

4. The output from the 10 dB attenuator then goes to the main amplifier, 

which can provide up to ±5 V levels into 50 

Ω

. An output relay can 

switch between ground level and the main amplifier. Refer to the 

 section of this document for additional information 

about this relay.

5. The output of this relay goes to a series of passive attenuators. 

6. The output of the attenuators goes through a selectable output 

impedance of 50 or 75

Ω

 to the I/O connector.

End of All Stages

f1 f2 f3 f4

Start Trigger Start Trigger Start Trigger

Start Trigger

Start Trigger

f1