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Application: Function/Arbitrary Waveform Generator Trial and Analysis
Release date: : 2020-01-07 11:36:31
Due to the recent demand for some signal generators, we made a general understanding of the signal generators on the market. Traditional signal sources use independent devices to form oscillating circuits to generate corresponding waveform signals with low precision, poor stability, weak user-friendliness and relatively simple function. We turned our interest to the currently popular DDS function generators.

Given our cost budgeting and project requirements, the agent recommended two domestic signal sources to us for trial, one of which was UNI-T's UTG2122B function generator. After detailed trial, we chose this function generator finally. The focus here is to summarize and share our understanding of this instrument in the last half month.

1. General Introduction of the Instrument
The function generator is a dual-channel arbitrary wave function generator with a maximum bandwidth of 120MHz, 1.28GSa/s interpolated sampling rate and 16-bit vertical resolution (vertical resolution: the vertical resolution, which usually represents the resolution of the amplitude of the generated waveform signal, is determined by the bit width of DAC in the signal source). It adopts many new technologies and processing methods based on the traditional DDS function generator, which overcomes the defects in the DDS principle (defects in the DDS principle: refers to the fact that as the waveform lookup table is affected by resources and the depth of the general table is relatively small, the waveform generated at a low frequency is discontinuous, a trapezoid may exit, and the generated waveform is relatively spurious with poor quality; when a square wave signal is generated, the edge always has a period of jitter). Thus, this function generator can provide pulse waves and arbitrary waves with high quality and low jitter for users.

In addition, the multiple modulation function of UTG2122B meets the cost and performance requirements of our basic electronic research and development, and its flat quadrilateral structure is suitable for the placement of our console and the superposition of other instruments.

2. Analysis on the Trial of Square Wave and Pulse Wave
One of the points that attract us about this instrument is that the square wave can reach the output of 80MHZ, and the minimum edge time at any frequency point can reach about 4ns. By disassembling, it is found that the instrument uses a mode that independently generates square waves. This fast-edge high-frequency square wave signal output is very suitable for our project.
However, the minimum edge time for the pulse wave of the other domestic function generator can only reach μs level at low frequency. There is no doubt that UNI-T's UTG2122B brings us unexpected surprises. Its jitter is almost invisible, the fast-edge overshoot can meet the requirements of indicators, and the edge can achieve 1ns steps. Why can so simple hardware design make such a good effect of the pulse wave? It suddenly aroused the curiosity of a group of engineers. They analyzed for a long time but they still could not understand how it was achieved. After searching on Baidu, they found that UNI-T had independent patents in this regard. Figure 1 shows the actual test chart when the pulse wave is 1kHz and the edge time is 8ns. The upper waveform is a thumbnail image, and the lower waveform is a waveform with a magnification of 20k times, showing the smoothness and beauty of the edge.

Figure 1: Actual test of 1kHZ pulse wave edge

3. Analysis on the Trial of Ramp Wave
For the ramp wave, we only focus on the symmetry of 0% and 100%. In these two cases, we have certain requirements for signal quality.
First, we set the parameters of both instruments to 1kHz, 1Vpp, the symmetry of 0.1% of output, and 100Hz, 1Vpp, the symmetry of 0.0%. The trial comparison is shown in Figure 2 and Figure 3 (the yellow waveforms are that of UNI-T's UTG2122B). By comparing the ramp waves, we think that the blue waveforms should be wrong. What we need are continuous and smooth waveforms.

Figure 2: Comparison result graph of 1kHz and 0.1% symmetry

Figure 3: Comparison result graph of 100Hz and 0.0% symmetry

4. Analysis on the Trial of Noise Floor
For us in the IC industry, in addition to the good performance of square waves, pulse waves and ramp waves, another crucial parameter to consider is the signal noise floor of the signal source's own output. How is it? Is the interference between its own multiple channels serious? Below we compare the noise floor of the two instruments.
First we test the interference between the two sources' own channels. Channel 1 of both instruments is set to 1MHz sine wave and 20mVpp output, and channel 2 is set to 120MHz sine wave and 4Vpp output. When the channel 2 output of both signal sources is off, let's look at the output of the channel 1. The actual test result is shown in Figure 4. The signal quality of the two instruments is almost the same. When the channel 2 is fully on, the situation is completely different. As shown in Figure 5, the yellow waveform is that of UNI-T's UTG2122B, and the blue waveform is that of the other domestic signal source.

Figure 4: The output interference of channel 1 when channel 2 output is off

Figure 5: The output interference of channel 1 when channel 2 output is on

Figure 6: Trial comparison of small signal and large DC

5. Summary
We only pay attention to the performance and function we need. Maybe there are certain advantages in other aspects for the other domestic signal source, but it does not meet our use requirements. Through this half-month comparison trial, we conclude that the appearance of the other domestic manufacturer is better, but the more we use it, the more we find its shortcomings. UNI-T's UTG2122B is just the opposite. Although the appearance is not dominant, the performance and indicators are excellent, and the operation is very user-friendly. Even the operators on our production line can quickly use it.