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AT2380v1 //  2 Channels digitally controlled stepped attenuator
AT2380v1 //  2 Channels digitally controlled stepped attenuator
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Old 26th August 2017, 07:48 AM   #11
Frex is offline Frex  France
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Join Date: Nov 2009
AT2380v1 //  2 Channels digitally controlled stepped attenuator
Hello,

I worked a lot this week on the CPLD software and now manual control is done and work very well. Output dBV measurement work also fine from -80 to +10dBV.
The last unterminated function is the control loop ofr tracking mode that is not yet completely functional. That will come soon, and then i will do a little video to present the system functionalities.

Frex
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Old 26th August 2017, 07:54 AM   #12
jcga is offline jcga  France
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Hi Frex,

Does it mean that you have tested the -80 to +10 dBV accuracy on the intended frequency range ?
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Old 26th August 2017, 08:11 AM   #13
Frex is offline Frex  France
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Join Date: Nov 2009
AT2380v1 //  2 Channels digitally controlled stepped attenuator
Hello,

The displayed dBV resolution is 0.5dBV, and it is also almost the accuracy of the measurement
in the -80/+10 range ( the AD8310 specs say +/-0.4dB). It work very well to many MHz.
Anyway, i don't have already made serious measurements on the instruments, i want to finish the software first.

Frex
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Old 26th August 2017, 08:21 AM   #14
jcga is offline jcga  France
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My question was about point 4 in your specifications list:
"Flat frequency response ( 0,05dB) from at least DC..1MHz..."
JC
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Old 26th August 2017, 08:57 AM   #15
Frex is offline Frex  France
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Join Date: Nov 2009
AT2380v1 //  2 Channels digitally controlled stepped attenuator
Ok,

I've done only few uncalibrated frequency response measurement and i can only
say for now that flatness is very good in more than 1MHz bandwidth.

Frex
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Old 26th August 2017, 09:05 AM   #16
jcga is offline jcga  France
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Excellent,
So standing by for the upcoming video then !
JC
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Old 18th September 2017, 07:42 AM   #17
jcga is offline jcga  France
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Hi Frex,
any news on your project ?
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Old 18th September 2017, 05:44 PM   #18
Frex is offline Frex  France
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Join Date: Nov 2009
AT2380v1 //  2 Channels digitally controlled stepped attenuator
Hello JC,

I must confess that i don't had much time these weeks to work on the project.
Anyway, the amplitude loop control start to work now, but some job need to be done before to get a good instruments.
I take also much time these to learn using ModelSim with the latest version of Quartus and writing test-bench files.
So, the learning curve is slow, but doing this for a real design is very motivating ! So no worry, work is in progress.

Frex
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Old 19th September 2017, 08:09 AM   #19
jcga is offline jcga  France
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Thanks for the update
Take your time
After all we are in a Diy forum...

JC
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Old 14th October 2017, 01:56 PM   #20
Frex is offline Frex  France
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Join Date: Nov 2009
AT2380v1 //  2 Channels digitally controlled stepped attenuator
Arrow AT2380 DIY stepped attenuators news..

Hello,

After much work, all the CPLD software is now almost done.
Tracking mode of the attenuator work very well now.

The output voltage of the attenuator can be tracked between +10dBV to -85 dBV,
regardless of the input voltage or output load.
That's A very convenient way to fit with particular level for THD measurement.

I added also a new functionality that allow to display output dBV level
in both Manual and Auto mode.
The level measurement work within +/-0.5dB error beyond MHz range.

In both modes, the step size can be choose to 0.5,1,3,6 or 10 dB/crank.
A 1s push allow to switch from Manual mode to Auto mode.

I made few bandwidth measurements, and the frequency behavior is very good.
Even if performance verification is not easy.
I used the Analog-Discovery to send a DC-2MHz signal and analyze
output of the attenuator for -20,-40,-60,-80 and -100 dB settings.
The result is show below.

Click the image to open in full size.

We can note that higher is the attenuation level and noisy is the response.
This is a boundary of the Analog-Discovery ( 14bits ADC..).

Now, some results in a lower bandwidth range (DC-96kHz),
with my AK5394ADC in V2/V1 mode (ratio of Vout/Vin of attenuator).
The result below to different levels.

Click the image to open in full size.


We can show on these measurements that frequency response is very flat,
even much beyond audio frequencies.
I also made 10kHz single tone verification where it is possible to verify
much higher attenuation level.

To complete the design folder, i started to wrote the user manual of the project.
But as promised, i will publish a small movie to present the AT2380 soon.

Frex
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