Technical Insights
New Realms of Rapid Application Development with Introspect’s Pinetree Software
3 min
Every once in a while, an electrical engineer would need to generate high quality signals such as sine waves, multi-tone waves, or arbitrary functions. For example, if you want to characterize the frequency response of an MCU analog input interface on your product, you might want to excite the interface with sine waves of different frequencies and check its response as a function of stimulus frequency. A typical tool for achieving this is an arbitrary waveform generator (AWG). But what if you do not have an AWG or what if you need 10 AWGs and not just one? This is exactly the conundrum we faced recently, and we decided to create our own arbitrary waveform generator using one of Introspect Technology’s very flexible products. Learn how we did this by reading on. Let us first review what an AWG is anyway.
Anatomy of an Arbitrary Waveform Generator
A modern arbitrary waveform generator relies on digital synthesis and digital-to-analog conversion technology. Referring to Figure 1 below, the waveform is first designed numerically in software. For example, if you want to generate a sine wave, this is typically designed as a high-precision sequence of numbers representing the sine wave values as they vary over time. The term “precision” here refers to the number of bits representing the quantitative value of the sine wave. If it is 32 bits, then the sine wave is represented with higher fidelity than with, say, 8 bits.
Figure 1: Block diagram of a typical AWG
The waveform samples are then stored in a digital memory inside the AWG. Finally, the waveform samples (still just a sequence of numbers) are “clocked” at a high frequency through a digital to analog converter (DAC). The DAC converts each number (i.e. each sample of the sine wave) into a physical quantity such as a voltage. Naturally, the DAC function is very critical to the operation of an AWG because it must convert some minute numerical values into distinct physical quantities such as voltage levels. For example, if the sine wave is represented by 12 bits, then the DAC needs to resolve quantities with a resolution of ~244 parts per million (1 / 2^12) of its full-scale voltage.
The cost of an AWG is often dominated by the cost of the DAC that is used inside it.
The SV5C-DPTXCPTX Has Not One, but Twelve AWGs Embedded in it!
At first sight, it might seem odd for us to bring up the SV5C-DPTXCPTX (Figure 2 below) in the context of this blog post. The SV5C-DPTXCPTX is a MIPI® D-PHY generator when operated in D-PHY mode, which is the mode that we are focusing on in this blog post. The fact that it is a pattern generator means that it generates digital patterns, and this is its main function. However, because of the rich impairment capability in the SV5C-DPTXCPTX, it actually contains some seriously sophisticated DAC technology.
Figure 2: The Introspect Technology MIPI generator is actually a lot more than that
Referring to Figure 3, each pin in the SV5C-DPTXCPTX contains its own AWG! That is, each pin has the usually rich pattern generation chain for MIPI testing, but it also has an integrated analog modulation path that allows us to create receiver test impairments (Common-Mode Noise Injection on the HS Portion of a D-PHY Pattern). In short, each SV5C-DPTXCPTX has 10 independent AWG instruments when operated in D-PHY mode and 12 when operated in C-PHY mode. This fact makes it a truly versatile tool for your lab testing needs. Read on to learn how we programmed the SV5C-DPTXCPTX to do just that.
Figure 3: Introspect’s award-winning pattern generation chain architecture
How We Programmed the SV5C-DPTXCPTX to Act as an AWG
First, we operated in D-PHY mode. As is well known, the product itself is a combo product, and it can support both D-PHY and C-PHY. While both modes have the fully functioning AWGs enabled in them, operating in D-PHY mode is slightly easier since we could just play an all-zeros pattern without having to worry about C-PHY modulation. In any case, referring to the following figure, we used the default Introspect ESP Software settings and simply added a CustomPattern component. In this component, we set the pattern type to be HS-only, and simply programmed the unit to generate an all-zeros pattern.
Figure 4: We started with programming the SV5C-DPTX to generate an idle pattern (no digital bits being output)
Then, we created a set of CommonModeNoise components as shown in Figure 5 below. Each of these components can be programmed independently, and it can be attached to any pin on the generator. So, for four data lanes and one clock lane, we needed to create 10 distinct CommonModeNoise components.
Figure 5: We added an independent CommonModeNoise component for each wire in the system — this makes 10 separate signal sources
Finally, the CommonModeNoise components were simply programmed to generate different signals, primarily sine waves in my current application. This was all we had to do.
Some Resulting Waveforms
The following figure shows four of the 10 signal sources displayed on a 4-channel oscilloscope. As can be seen, each channel is generating its own sine wave. In this particular case, we programmed all sources to generate the same amplitude sine wave but to have four distinct frequencies.
Figure 6: Four of the 10 AWG channels, each producing a different frequency sine wave
Next, we programmed unique amplitudes on each signal generator. So we brought all the frequencies to the same value. Then, we selected a different amplitude for each channel. As can be seen, it is very easy to generate these waveforms from within the Introspect ESP Software.
Figure 7: Four of the 10 AWG channels, each producing a different amplitude sine wave
Finally, here are some waveforms at 1 GHz. In the following figure, the outputs of the signal generators were routed to a device under test (DUT), and we see the different phase response of the DUT. The blue and red waveforms have a different phase from the yellow and green waveforms.
Figure 8: DUT response to a 1 GHz stimulus on 4 channels
Conclusion
So, there you have it: with a single SV5C-DPTXCPTX, you can generate 10 independent sine waves at frequencies of up to 1 GHz. This is a great deal of performance, and it allows you to leverage existing equipment in your laboratory to create really creative solutions. At times of recession and reduced capital equipment budgets, it helps to know that you can rely on your trusted Introspect Technology SV5C-DPTXCPTX in order to keep innovating and keep generating signals!
