Sensetivity of the ADC input

[ASDFG123]

Hi, what is the level of sensetivity of the 125-14 and 122-16 boards? Conditions is the sine signal 10-15 MHz, both boards terminated to 50 Ohms (125-14 externally), both have simple osciloscope flash program. I did not noticed any advantage of the 122-16 board, actually 125-14 is better. Both see signal from 0.5 - 1 mV RMS, but 14 bit board has wider dynamic range.
Is this result that should ber or I have some mistake?

[Yevgeniy]

Hi!
I have the same question about sensivety of SDRlab 122-16.
We did tests and the results are below.
Input signal: 200mV RMS

https://drive.google.com/file/d/1DLp82E ... sp=sharing

Input signal: 370µV RMS

https://drive.google.com/file/d/1xk4VnW ... sp=sharing

Input signal: 120µV RMS

https://drive.google.com/file/d/19EGX9O ... sp=sharing

[pavel]

Both see signal from 0.5 - 1 mV RMS, but 14 bit board has wider dynamic range.

On the 122-16 board, changing the position of the jumper connected to the SENSE pin of the ADC chip increases the dynamic range by 6 dB without decreasing the sensitivity.

[Yevgeniy]

Hi Pavel,
I couldn't found any jumpers on SDRlab-122-16.
Maybe you mean STEMlab-125-14?

[pavel]

I couldn't found any jumpers on SDRlab-122-16.

These are solder jumpers shown as 0 Ohm resistors R15 and R16 on page 3 of the 122-16 schematics.

To increase the dynamic range, R15 should be unsoldered and R16 should be soldered.

[Yevgeniy]

The SENSE pin change input range from 0,5V to 1V. It's clear.
But it's not solve problem because we does couldn't to digitize signal below 200 µV.

[pavel]

Yes, my comment was about the dynamic range. On the 122-16 board, it can be increased.

If your signal is periodic and your application does not require 60 MHz bandwidth, then I think the sensitivity can be increased by downsampling.

[pavel]

I have just done a few quick checks and calculations.

The LTC2185 ADC on the 122-16 board has an SNR of around 76.8dB for the +/-1V input range.

The ADC noise amplitude can be calculated as

1V / (10^(76.8dB / 20)) = 145uV

This seems to match what you observe quite well.

edit: just noticed that the WBC4-1TL transformer has a turns ratio of 1:2 and it should add a factor of 2 to the noise amplitude calculation at the board input (72uV).

[redpitaya]

Full ADC performance measurements can be found here:
https://redpitaya.readthedocs.io/en/lat ... astIO.html