Mixed signal oscilloscopes or MSO’s, scopes that integrate a Logic Analyzer,  have been around around for ages. They are undoubtedly super useful pieces of equipment for any electronics engineer (or even hobbyists!). However, recently some firms started releasing Logic analyzers that support analog capturing. In this article, I’ll be explaining why we don’t think it’s a good idea.

Disclaimer: Before I continue, let me stress on the fact that I believe the companies releasing such devices are very respectful and respected competitors, i am just informing our position on the subject, to whom it may concern!

So, to put things simply, we think that a logic analyzer whose probes can be used to capture both analog and digital signals would end up being a toy, an expensive one, but not a reliable measurement device. Here’s why:

Sampling rate is not bandwidth

Look carefully at the analog sampling rate of that analog-capable logic analyzer. Chances are it will be below 100 MSPS (million samples per second). This may be due to hardware or economic limitations. What ever the reason is, 100 MSPS is not even close to what you’re used to have on a classic low cost Scope.

With a sampling rate of 100 MSPS, you can only start to clearly see analog signals having a frequency of 5 MHz (like a square wave clock signal). With a sampling rate of 10 MHz, don’t expect to reliably capture any analog signals having a frequency higher than 500 KHz. This, is in many cases, makes such a device, well… useless.

What that means is that you would get a half-baked scope-like features that can’t compete with the lowest cost Rigol scope on today’s market! We don’t want to offer you that! not even for free!

Logic Analyzer probes are not oscilloscope probes

If you are info electronics in a way or another, you would probably recognize in a glance what’s in the picture below. Good old oscilloscope probes! (and the tektronix scope laying on my desk, by the way!).

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Oscilloscope probes may have evolved a lot during past decades, but some of it’s mains characteristics remain:

  • They are shielded
  • They have very low inductance
  • They are compensated for their stray capacitance
  • They have attenuators that further decrease their loading on the circuit.

I could write a lot about each and every one of those features, but the bottom line is: those probes will capture very low voltage signals with high degree of fidelity, without impacting the operation of the measured circuit.

Again, what that means, is that logic analyzer probes cannot be used to measure analog signals. Those probes are quite susceptible to transient noise.

A Scope, a Data Logger or a Logic Analyzer

You can’t have those three features in one low cost device. Even if you would find such a device, would you really want it? Those three kinds of devices exist independently for a reason. If there is no reason to have those devices combined “all-in-one”, then you’ll be better off using each device independently.

  • An oscilloscope’s design is optimized to collect a small amount of data but at a very high refresh rate
  • A Logic analyzer is optimized to capture a important amount of data while performing real time or near real time processing and decoding of the data.
  • A Data logger is designed to capture huge amount of brute data without any real time analysis or processing. Data may be analysed after being collected.

As you can see each device is optimized in such a way to give you maximum usability for specific applications, and that’s why we are careful when combining multiple functions in one device.

OLYMPUS DIGITAL CAMERA

 

Yesterday at work i did a really cool thing with the new Hex View feature of ScanaStudio, and I though i would share that with our readers! I used ScanaStudio to write a CMOS camera initialization function in minutes instead of hours! more

FTDI chip provides really excellent USB chips, that will handle all the USB communication for you with really excellent bandwidth performance. FTDI provide an exhaustive documentation for their cross platform driver. In contrast with the VCP (Virtual Com Port) mode, the D2XX driver allows direct access to the USB device ports in a completely transparent fashion. The Windows drivers are already certified by Windows, so you can just pick your favorite chip from FTDI, and use it in your product without having to worry about time consuming driver development and certification.

All those arguments make FTDI a very good choice if you are willing to launch a cross platform USB based product as we did for ScanaPLUS. However, be warned, there is One Big Problem you will face on Linux platforms. This short post is all about this problem, and the solution we found to overcome it in a nice, transparent and beautiful way. more

In 2012, we have released an “educational KIT” version of Scanalogic-2. One of the main objectives of this KIT is to show in a fun way how a logic analyzer works. When building/mounting a SCANALOGIC-2 EDU KIT, you will notice that there are 6 distinct blocks. Each one of those blocks is described below

 

Power supply block

Provides stable and filtered 3.6V for the SRAM (memory) ICs and for the buffer ICs.

USB signal conditioning block

Allows the matching between the USB signal levels and the micro controller’s 5V signals.

Clock Block

Provides a 20MHz clock for the operation of the micro controller and for the signal sampling. This clock is stable to +/- 50 PPM (Pulse Per Minute). The stability of this clock is very important as the precision of the whole logic analyzer depends on it.

MCU Block

The Micro controller block is by definition the heart of the device. It received the capture request from the host (PC) application, initializes the SRAM ICs, watches for trigger conditions and records the exact trigger position. It sends the captured samples to the host application for further analysis and visualization.

SRAM Block

The SRAM block holds the sampled data. There are 4 SRAMs and each one is dedicated to one channels: Each byte of data represents 8 consecutive samples, one for each bit. The main idea of the design is to to feed the samples directly into the SRAMs, without passing by the micro controller. This is the only way to achieve the maximum sampling frequency of 20 MHz.

BUFFER Block

This part is – by definition – used to isolate the outside world from the logic analyzer. However, in this design, it is also used to allow interfacing to a variety of logic levels, from 2V to 5V.

As you may already know, we have been producing SCANALOGIC-2 Logic analyzer in big quantities for the latest 15 months. This have been our first major product, and over the time we have learned how to (or built ways to) automate most productions steps. Programming the atmega chips (which controls the SCANALOGIC-2)  can take a lot of time. Specially if you have to do it 500 times. Of course, one solution is to buy pre-programmed chips, but this is not always financially interesting. more

AtXmega micro controllers are quite special. Even If you are familiar with standard AVR micro controllers like the AtMega 168 (used in arduino), there are many aspects that can discourage you from migrating to Xmega.  more

Today I am going to talk about low cost and effective image processing for very specific embedded applications. I am not talking about robots recognizing their environment or finding their way to a power plug, but rather using small CMOS camera as better sensor. We have used this technology for various clients more