Going from TDS3012 to MSO44

In the past 18 years I have been using a 100MHz two channel oscilloscope TDS3012B from Tektronix, which was using the new at the time Digital Phosphor technology (DPO). With a bandwidth of 100MHz back then it was sufficient for embedded design and debugging. I was missing the serial decode capabilities, but I was able to program a Python script for this purpose. For more information see my article in CodeProject.

Debugging a system with Atmel AVR and Xilinx Spartan (5K gates) device
Debugging a system with Atmel AVR and Xilinx Spartan (5K gates) device

Back then it served me very well, although in some cases I would like to have four channels to help me resolve some problems. Not a showstopper anyway, I have been used to have less than ideal equipment. Recently the ethernet interface failed and this reduced the capabilities of my old instrument. In addition, my newer embedded boards started using SDRAMs or HDMI and the signal bandwidth of the scope was below my debugging needs. I had to guess the clock phase on my FPGA-SDRAM interface looking to sinewaves on my scope and trying an educated guess for the correct PLL phase delay. Fortunately, the first guess for the phase difference was correct, so this went smooth and my SDRAM worked fine without much hassle. The old floppy also prohibited data transfers or firmware updates.

According to Altium Designer research about new PCB designs, the trend is to go to boards with 500MHz. Although this might seem a little high for microcontrollers, I started feeling the pressure to go above 100MHz and for some newer serial protocols even higher. I had a SDRAM 133MHZ, but DDR starts to be more mainstream even for embedded systems. Purchasing a scope is an investment for the next 10 years and hence the capabilities should match at a great extent the future requirements. If we go to platform FPGA boards, like Ultra96 or PynQ, there are serial interfaces that can achieve clock frequencies above the 100MHz limit. So, I thought that my next scope should be certainly at the range of 350MHz. So, I decided to move on to a new scope like the MSO44 from Tektronix. A big thanks to Vector Technologies which helped me with my decision. In the next paragraphs, I will present some of the features from my preliminary tests of the new instrument. I still keep my TDS3012B around, as a secondary instrument for field work.

Last days of my TDS3012B Sitting on my lab, while expecting the MSO44.
Last days of my TDS3012B Sitting on my lab, while expecting the MSO44.

Thank you TDS3012B for your service all these years!!

MSO44

The new instrument has four analog channels. This alone is an important upgrade. I can check full SPI bus with enables and clocks or combination of analog and digital lines on my board. A rarely used more than 4 channels unless I had to deal with a digital parallel bus.  Even then looking at some control signals and one of the data could give you an idea of the situation. Nevertheless, an analog probe can be replaced by a digital counterpart with 8-channels digital inputs and used as a logic analyzer. You lose one analog channel for this, but it is a reasonable compromise. Other vendors provide this functionality without the analog probe loss, but I do not believe or remember a case in the past that this would be an issue.

A quick view of the MSO44 in action
A quick view of the MSO44 in action

The next major upgrade is the bandwidth of 500MHz. Hey, I can check my SDRAM clock easily now… I want to check at some point my HDMI signals (at 250MHz). The 500MHz though can be used also for RF applications at 433MHz, through the spectrum analyzer feature. Really neat.

The arbitrary function generator feature is really useful as with one instrument I can also exercise my circuits. I plan to use this feature for testing the Hydrophone Analog Front End and the FPGA data capture.

I am not going to stay at the UI features most instruments in this category have recently, the large touchscreen etc. Having a large screen estate is important to view multiple signals.

One important aspect of the new generation of instruments is that they offer upgrades by license. So, you can upgrade the bandwidth or some features (more serial busses decoding etc) by purchasing them later according to your needs or projects. This provides a more viable solution where you start with some specific requirements and you can scale up the instrument according to your needs later-on.

Serial Decode

The instrument supports serial decoding of common protocols like RS232, I2C or SPI. This is useful for debugging peripherals or components to your microcontroller. To test this feature  I tried an I2C interface on one of my boards. The abundance of screen area is useful to put all the signals without too much clutter and in addition have the serial bus decoding.

Serial Bus decode of an I2C bus
Serial Bus decode of an I2C bus

Web Interface

Connectivity is important, so the instrument comes with a bunch of USB ports and an ethernet port for network. This is what I used with a web browser to mirror my MSO screen to my desktop PC. Extremely helpful if you want to control the instrument from the same place as you control your debugger. No need to turn your chair around to turn knobs.

MSO screen view on my desktop PC
MSO screen view on my desktop PC

Jitter Tests

On one of my boards, I knew that there is some jitter on my clock. So, I decided to test the DPO capabilities and look in more detail on this signal. I can see the probability of states clearly. I want to delve more on this feature in the future.

Clock Jitter seen through DPO
Clock Jitter seen through DPO

Spectrum Analyzer

Yes, many engineers would say that this is the FFT button or feature found on most of the scopes, so what’s the big deal. Well, nope. The FFT feature exists in the math menu and is not the same with the spectrum analyzer feature, which works like a spectrum analyzer. I mean you need to setup video bandwidth, resolution bandwidth and so on, as you would do in an actual spectrum analyzer. In addition, changing the time domain signal (scaling-resolution) does not affect the spectrum and vice-versa. I read about this feature on the website when looking at the specifications and I was keen to see it in action. Having worked with spectrum analyzers in the past, I got pretty familiar with the parameters. This feature exists inside the channel settings (tap on your channel and select spectrum tab). Testing this feature, I tried a remote of 433MHz. The probe was attached at the antenna signal on the receiver side.

Spectrum of a remote at 433MHz
Spectrum of a remote at 433MHz

I even went further. I have some LoRa devices working at 433MHz and wanted to confirm that this is their center frequency. As LoRa uses broadband transmission, I set-up my instrument to capture and hold the maximum level. So after a while transmitting, the spectrum started to show activity, by filling bands.

Spectrum max hold at 433MHz LoRa transmission
Spectrum max hold at 433MHz, LoRa transmission

Arbitrary Function Generator

Providing stimulus to your circuits is essential when designing and testing analog to digital converters. Applying some basic stimulus may help you check design elements and ensure that the basics work. For more thorough testing you will need a dedicated instrument. In this case the arbitrary function generator is used for the first line of defense. Here a sinc function is output and its spectrum is displayed.

Arbitrary Function Generator and Spectrum
Arbitrary Function Generator and Spectrum

Conclusion

I will need to spend lots of time to test every aspect of the new instrument. I am already using it in my projects, and I am getting used to it. Albeit the complexity of the functions, I can navigate around, put the right settings without hassle, giving me time and insight and let me be productive. I have a long queue of things that needs development and testing that this instrument will help me a lot.

Our laboratory is now massively upgraded and ready to win the next battles!

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