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Why do I need a Mixed Signal Oscilloscope?

by admin on Thursday, May 29, 2014 7:58 PM
Introduction We get mails from people wondering how a mixed-signal oscilloscope differs from a regular oscilloscope, or perhaps wondering why an MSO is better than regular scope + a logic analyzer. And depending on the type of work you do, there might not be any difference. You might not need to look into the analog and digital realms at the same time. Some days you are studying why a switching supply isn’t working as expected, and then the next you are working on a SPI problem. And the two domains never intersect.

But for those that spend time working on complex mixed signal problems, a mixed signal scope lets you see things that you otherwise can’t see with separate tools because it shows you the analog and digital domains aligned in time. We recently found ourselves confronted with a problem that was not making sense and decided to write it up as a case study. We fixed the problem in the FGPA fairly quickly once we saw the bigger picture. It would have been nearly impossible to do so with just a logic...

Connecting to QuantAsylum Devices from C++

by admin on Saturday, March 22, 2014 11:10 AM

Generally, when we post articles on writing code to control your QuantAsylum hardware, the language of choice is C#. C# is a managed language, meaning there is an entity that is actively managing memory in the background. VisualBasic is also a managed language. C++ as offered by Microsoft has two flavors: Managed and unmanaged.

Managed C++ allows the developer to worry less about memory management if they want to. But more importantly, it fits into a larger framework Microsoft has built in which mirrors the framework available to C# and Visual Basic. This means the developer has access to rich run-time libraries that are very well thought out, sophisticated syntax for selecting data, and tool flows that all work the same. Overall, it allows the developer to reap all the benefits of a more modern language and infrastructure while still sticking with what they know.

Unmanaged C++ is how things have been done for the last 20 years, and there are countless apps written in (unmanaged)...

QuantAsylum Connection Manager

by admin on Saturday, March 15, 2014 11:42 AM
Controlling QuantAsylum products from code you have written is simple, and it’s about to get even easier if you are trying to control a device that resides on the same machine.  The previous way of doing things is still required if you are going to connect to your device over the internet. But most of the use cases our customers require don’t require a truly remote connection, and thus the shortcuts below should be helpful.

Architecture Background Below you see a simple picture of how the different pieces co-exist. The QA Application is how you interact with the hardware. It is the screen of the oscilloscope or power supply that runs on your PC. And of course, the QA Hardware is the physical box that captures the different signals required. And the QA application and QA hardware connect over USB.

The User Application can be written by anyone. What is important is how the user application connects to the QuantAsylum application. Historically, applications have relied on GPIB, which is a popular (albeit...

Power Quality Analysis with the QA100

by admin on Sunday, March 09, 2014 11:03 AM
Overview Note: 16-Mar-2014: The Power Quality Analyzer app is located here

We’re finishing up a free application for the QA100 that will let you turn your scope into a single-phase power quality analyzer and recorder. A power quality analyzer allows you to look at the short and long-term quality of AC power, and also gives insight into how a load consumes that power. These tools are useful to those trying to diagnose power quality problems or to those working on advanced consumer electronics that might be concerned with power factor correction and the Energy Star (or other) power factor requirements for consumer electronics.

To use the application, you need a QA100 oscilloscope. You will also need a differential probe and current clamp suitable for the power you wish to measure. DO NOT ATTEMPT TO USE THE QA100 on line voltages without a differential probe. See the manual for why this isn’t a good idea if it’s not...

QA400 IMD Measurements

by admin on Tuesday, October 08, 2013 12:23 AM
Intro We will look into adding the ability to make automatic IMD (Inter-Modulation Distortion) measurements on the QA400 at some point in the future. Part of the reason we’ve held back is that there are a lot of variations that are possible in IMD measurements and it’s not yet clear if a subset will do the trick and get us 90% of the way there or not. This post will look at the types of IMD measurements, and show how these basic measurements can be made on the QA400 today.

The purpose of IMD measurements is to characterize the non-linearity of an amplifier while its being subjected to more than one tone. This is the “intermodulation” part of the Inter-Modulation Distortion Tests. THD, or Total Harmonic Distortion, is concerned with the amplifier’s ability to render a single tone.

Any amplifier that has non-linearities will “mix” two or more tones. Mixing is the process of multiplying two waveforms together. The result, in the simplest terms, is that you produce a resulting waveform that bears no...

QA100: Expanded Logic Channels and HW Triggering on I2C

by admin on Saturday, April 06, 2013 11:36 AM
We’re finalizing some new features for the QA100 that will soon be available as a pre-release. We’re posting this here to invite any comments or feedback.  In short, we’ve added the ability for the QA100 to now function as a single 8-bit analog scope with 24-bits of logic analyzer. The default mode to date has been two 10-bit analog channels and 12 bits of logic. Additionally, we’ve added in the ability to trigger on I2C transactions in hardware. This means you can program in an expected address, read or write, ACK, a single data byte and another ACK, and if those all match, then a trigger will occur in hardware. This means you can hang the QA100 off a busy I2C bus and trigger on a transaction that targets a specific part on your board. The HW capture is clocked at 30 MHz, meaning I2C buses at even 400 KHz aren’t a problem. Currently, there’s not any HW filtering, so noise on the bus clock line can cause problems. Because we’re running at 30 MHz, however, there’s the opportunity to add in some oversampling and...

Melt the noise away….

by admin on Tuesday, March 12, 2013 8:35 PM
An email from DM shared an app note from AKM on enhancing the dynamic range by using stereo channels to sample the same signal, and then averaging the acquired signal to reduce the noise. In the app note, experimental results are shown in which they first used the L+R channel to sample the same signal and improve the noise by 3 dB.  Next, the experiment was repeated by adding another converter, and  they used 8 ADCs sampling the same signal, with each of the 8 ADC outputs averaged to give the improved resultant output.

This works due to the nature of noise. Below in red, you see the distribution of 100,000 normal random numbers. In blue, you see the distribution of another 100K points, except this time they were generated by averaging two normal random numbers. And finally, with the green trace, you see the result of averaging 8 normal random numbers. The key point to understand here is that as you average more and more noise samples, the result...

Extending the QA400 Noise Floor with a Pre-amp

by admin on Thursday, February 28, 2013 10:53 PM
From the previous post on the Apple iPod, we saw the QA400 had a noise floor that had a few dB of margin to the latest iPod Nano. But it is possible to improve that? It certainly is. And the easiest way to do that is with an external low-noise pre-amp.

Pre-amps are easy to add externally. Internally, they can be a bit more difficult to build-in to the product if you are looking to keep the cost reasonable. As you push deeper into the noise floor, the power supplies must get cleaner, the internal shielding needs to improve, and of course relays are required to route the audio into or around the pre-amp on. If you leave it on all the time, then you reduce the maximum signal you can cope with. Additionally, extremely low noise pre-amps can have some difficulty coping with large signals and high slew rates. The QA400 seeks to strike a balance by offering a dynamic range tailored to span from just below the noise floor of very good consumer and pro audio equipment, up to and including the levels generally encountered...

Apple iPod Nano

by admin on Sunday, January 27, 2013 2:13 PM
Below are some brief measurements using the QA400 USB Audio Analyzer on the iPod Nano with 2.5” touch display.

Unless noted, the measurements below used test tones that were 24-bit 48Ksps wav files created in Audacity and dragged into iTunes. And unless noted, all measurements were made with a 16 ohm load. Volume settings were set to max. Test loads were resistive.

Output The player shows a solid 983 mV drive into a high Z (open circuit) load with a 0 dBFS source file. For comparison, the Sansa Clip+ is about 564mV under these conditions, and the FiiO E17 is about 2.5V. Note for amplitude measurements, the Flat Top window is used due to its low ripple. The low ripple comes at the expense of slightly higher noise floor and resolution. So, be careful in comparing plots made with different windowing functions.



QA400 Measurements on SURE 2x50W TDA7492 Class D Amplifier

by admin on Sunday, November 04, 2012 8:45 PM
The SURE line of class D amps are economical amps deliver some fairly big specs. Class D means that they are switching amplifiers, which normally boast much improved efficiency over Class A and Class AB amplifiers. The silicon and efficiency also lends itself to straightforward miniaturization.

Parts-Express and others offers a range of these amps, ranging from a few watts up to several hundred watts. As we hit the final stretch in checking out the QA400, we wanted to make sure there were no issues with high power, class D amps and external attenuators.

The input limit on the QA400 is +6 dBV and +/-5V DC. Class D amplifiers usually operate from a single supply, and as a result they usually operate the speaker in a push-pull fashion. The average DC across the speaker is zero, but the outputs idle at roughly the supply voltage divided by 2. The SURE amp here was no exception. With a 25V supply, the outputs idled at 12.5V.

Measurement Directions While the QA400 is readily suited for measuring...