Redpitaya Forum

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?

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

ASDFG123 wrote: ↑

Tue Feb 08, 2022 7:15 am

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.

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

Yevgeniy wrote: ↑

Thu Feb 10, 2022 9:21 am

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.

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.

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.

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).

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