AD3 performance problem's

[Ola]

Is there a performance problem with my device?

When I want to check the performance with external "Loopback" (14 bit DAC to 14 bit ADC) of the AD3 I got:

1.1MHz, 125MS/s, Enob 7.2 with FS=10Vpp
Averaging=50

INL/DNL 14bit DAC/ADC full scale 10Vpp
1LSB=0.61mV (external loopback)
DNL=2.5mV ~12bit, INL=20mV (10Hz and 125MS/s)

This is quite far off of the internal DAC/ADC spec.

Could somebody else do the same to check the AD3 performance?

[attila]

Hi @Ola

The oscilloscope channels of AD1,2,3 have two input ranges, 5V and 50V. At 10V the ADC is used at about 11.5bits

[Ola]

Could you also try try INL/DNL measurement's. As you could see the HD2 and HD3 is quite low. This is my measurement's:

[attila]

Hi @Ola

See the following:

 

[Ola]

I am not talking about discontinuity? I am doing 10 averaging and calculate the INL (Read plot) and DNL (Green plot). There are a loot of variation in the INL curve that is related to SFDR. The DNL is related to SQNR. There sesames to be something wrong also in the SFDR calculation in the measurement tool?

[attila]

Could you tell me the math used for INL DNL ?

[Ola]

M3 is for INL and M4 is the derivate of M3 => DNL. W1 is just generated as a triangle wave with 10Hz and amp=5V.

M3 is offset compensated with "-1.5e3"

M3:

5*asin(sin(2*PI*10*Time))*2/PI - W1-1.5e-3

M4:

if(isNaN(prev)) prev = M3;

var dif = M3-prev;

prev = M3;

return dif;

[Ola]

This equation for INL is an good approximation. If you want a more precise result you have to take all sample's accurate position and make a histogram calculation. The best method is to use the histogram method to a sinewave input (this is a separate discussion).

[Ola]

You could read more about this at : https://www.analog.com/en/technical-articles/histogram-testing-determines-dnl-and-inl-errors.html

[attila]

You want to perform the math on the digital loopback of W1 ?

54 minutes ago, Ola said:

5*asin(sin(2*PI*10*Time))*2/PI - W1-1.5e-3

W1 channel capture in Scope represents the digital samples sent out to the AWG1 DAC. However on your screen W1 is unchecked and if you have performed the capture this way, you may not have data to process.

[Ola]

In the datasheet from TI on the 14 bit DAC and ADC used in AD3 the INL and DNL is very good (< 1LSB).

[Ola]

Sorry, in the M3 equation it should be C1 not W1. and the offset compensation is "-1.5e-3".

(I did some other calculation in-between when I send the equation to you.)

[attila]

The IC spec sheets only refers to the IC itself, not including the frontend and nearby radiation sources.

Again, note that with 1V/div the ADC is high range ~50V pk2pk, with my AD3 62.82V, LSB 3.83mV
and here DAC + ADC is measured

 

Here the ADC is in low range, ~5V pk2pk, LSB 335uV
DAC LSB ~670uV

 

With 1V amplitude the DAC is also at low range LSB ~170uV

[Ola]

Thanks a lot for this measurement's. I have similar result's in my AD3 over the same region's that you measured. I know that the system could look a lot different than a pure DAC/ADC chip. That's why I wanted to do this measurement's. I am a chip designer myself with a loot of experience in this area. I really like the idea with the AD3 and the software and look's forward to the next generation. Hope you could increase the the sampling frequency and BW to support the next generation baseband (350MHz). Maybe you also could built in some support for different RF-BB modulation/demodulation in the software.

[attila]

Hi @Ola

The device internal noise (+nearby equipment radiation influence) can be measured by shorting the inputs.

[Ola]

Normally you do this with an open. When I do this with an open I have 1.55mV ACRMS. To see some problem's with on board component's in the chain you normally that with a spectrum analyzer and a known clean and filtered sine wave that have a frequency that is not an multiple of the sampling frequency (Prime frequency). By doing this you could see any unlinear or DC-DC coupling behavior in the system.

[Ola]

When switching range to 1V/div the input noise is 12.0 mV ACRMS. This is of course normal when you have to have an attenuator in the signal path.

[Ola]

It could be good to have a system datasheet available with all the most relevant measured data included. Like the normal datasheet from Analog Devices or TI with included typical waveform's like INL/DNL HD2/HD3, IM2/IM3 measurement's.