Hello everyone, my name is Sean Lee and I'm an engineer at Agilent Technologies
In today's video, I'm going to share with you how you can test low voltages or logic level audio ICs with the Agilent U8903A audio analyzer
Here's an overview of the test set-up. We are using a digital to analog IC evaluation board as our DUT today.
Of course, you will need a power supply to power up the DUT as well as a Digital Multimeter to monitor the IC's power supply voltages(Vdd) of DUT.
Last but not least, you need an audio analyzer, which will be using U8903A with digital audio option.
What you need is to generate a SPDIF signal to the DUT while the DUT output signal will be route back to the audio analyzer for analysis.
The first thing that we need to measure is the minimum working voltage. To do this, we will use a measurement function called Audio Bit or to be more specific, walking zero.
This function is basically designed to monitor the transaction status of each audio bit.
When the IC or DUT handle the transaction correctly, you will see the 0 bit rotate or walk along each bit, hence the name walking zero.
If the DUT stops working, the 0 bit will stop.
This is a test often used by R&D engineer to check on the working status of the audio IC during circuit design.
Now let's start the test. We will measure the minimum working voltage using two different settings/scenarios.
First we will use a input logic level of 3.3V which we already preset earlier.
This is the common settings found on most Audio Analyzers in the market.
Next,we gradually lower down the DC power supply voltage.
As you can see now, power voltage is at 3.3 volt and my "Zero" bit is now rotating or walking.
As we gradually lowering down the power supply voltage.
You may start to see some bits showing Zero, this should be fine
As soon as the bit still rotates,
What we try to achieve to take the measurement when the "Zero" completely stops.
As you can see, at 2.4 volt the 0 completely stops. If you take a look at our DMM and the reading is DMM is 1.57 V. This is the minimum working voltage.
For scenario 2, we will repeat the same test, only this time, we are using a much lower input logic level of 1.2V.
After we set that, go back to the earlier "Audio Bit" screen.
And again, we gradually lower down the power voltage until the "Zero" bit stops.
The "Zero" bit stops completely at 2.0 volt, and take a look at the reading of DMM. It's showing the minimum working voltage of 1.14 volt
So the question is, why is the test result different? Which one is the correct measurement?
This chart show is drawn based on our test results. It clearly shows that with only changes of the input logic level from 3.3 V to 1.2 V,
which is to match the DUT's output, the minimum voltages improved from 1.57 V to 1.14V.
Let me explain why this happens
First of all, when we set the audio analyzer input logic level to 3.3V, which is a fix setting found on most Audio Analyzer
the DUT stops working at 1.57 V. Is this true? The answer is a resounding NO!
As a matter of fact, the DUT is still working, but the audio analyzer could not interpret the logic correctly with a fixed 3.3 V logic level.
As the DUT voltage gets lower, the DUT's logic level will decrease as well
if the Audio analyzer is not able to reduce or interpret lower logic level, this will caused test errors due to incompatibility.
Thus, by lowering the logic level to 1.2 V to match the DUT's output in scenario 2
we are able to measure the true minimum working voltage.
In short, most modern audio ICs are heading towards low logic level design
and if your audio analyzer does not allow you to adjust or measure low logic levels,
you will not be able design and evaluate your ICs correctly
The Agilent U8903A is designed specifically to solved this issue
as it has the widest logic level from 1.2 V to 3.3 V
and allows user to input any value in between.
For more information, please visit
www.agilent.com/find/audioanalyzer-demo
Hope that this sharing was useful
and thanks for joining me today.