VT DSO-2A20 Manual Rev. 1.1
Virtins Technology
the noise rejection hysteresis (in percentage) for HNX option. Please refer to the hardware
specifications in the next chapter for the detailed specification of the rest of options.
1.8.4 Oscilloscope Persistence Mode
Under persistence mode, up to 200 most recent waveforms are kept in the computer memory.
These waveforms can be superimposed/drawn in the oscilloscope window in three ways:
Phosphorescent, Rainbow, Equivalent Time Sampling. Persistence Mode can be activated by
right clicking anywhere within the oscilloscope window and select [Oscilloscope Chart
Option]> “Persistence”. Please refer to Multi-Instrument software manual for details.
1.8.5 External Trigger Input Channel as a Digital Input Channel
The external trigger input channel of a second-generation VT DSOs can be used as a digital
input channel. It is actually a 1-bit ADC with the threshold for digitization adjustable. This
channel can be configured via [Setting]>[ADC Device]> “Digital Channel Configuration”.
If the external trigger is selected as the trigger source, then the threshold for digitization can
also be adjusted by adjusting the trigger level in the main window. With two analog input
channels and one digital input channel, the oscilloscope can be used for mixed signal
measurements. It can also be used as a protocol analyzer for serial communications.
1.8.6 Anti-aliasing filter for Spectrum Analyzer
The USB DSOs in the market are generally equipped with only one fixed anti-aliasing filter
for the highest sampling frequency. Aliasing will still occur when the sampling frequency
goes down. This will cause wrong measurements in both the oscilloscope and the spectrum
analyzer. The second-generation VT DSOs solve this problem using anti-aliasing filters that
can adapt to the sampling frequency. 16-bit resolution should be used to fully utilize this
feature. Please refer to the hardware specifications for details.
1.8.7 Signal Generator DDS and Streaming Modes
The signal generator of the second-generation VT DSOs features advanced hardware based
DSP algorithm which supports both streaming and DDS
（
Direct Digital Synthesis) modes.
Complicated signals such as white noise, MLS, frequency sweep and amplitude sweep,
which generally are not found in other USB signal generators in the market, can be generated
using the second-generation VT DSOs, for both streaming and DDS modes.
Under streaming mode, the output data are computed, continuously if necessary, by the
Multi-Instrument software in the computer and then streamed continuously to the DAC
device for output. One advantage of using streaming mode is that you can fully utilize the
power of the Multi-Instrument software to generate very complicated signal at minimum
hardware cost. However, limited by the software computing and the streaming speed, this
mode is not able to provide high frequency output. Also, it may consume a lot of CPU time
when the output sampling frequency is high or the output signal is complicated. Whether the
output signal is continuous or not depends on the system throughput, sampling frequency, bit
resolution, number of sampling channels, etc.
Under DDS mode, the computer only needs to send the output signal parameters (such as
signal frequency, amplitude, waveform type or shape data, etc.) to the DAC device and the
DAC device will take care of the rest. No actual output data will be sent from the computer
to the DAC device. This greatly reduces the CPU work load and communication traffic
between the computer and the DAC device. Very high signal frequencies can be generated if
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