I am using PXI 5124 (200 MS/s, BW:150 MHz) for acquiring photoacoustic (PA) signals ( PA signals are the same as ultrasound signals).
A transducer 75 MHz is used to detect the PA signals, then these signals are amplified (54dB) to PXI 5124. It's working well.
Now, I want to use PXI 5153 (2GS/s, BW:500 MHz), and noise appears. Please see more details in the attachment files
I use the same configurations for both PXI 5124 and PXI 5153 which are passed self-calibration.
Can you let me know what is wrong with my settings? is there any problem with my PXI 5153?
Thanks in advance
Solved! Go to Solution.
First 'obvious' deviation:
The lower noise 5124 has 12 bit resolution ... the 5153 has 8 bit. ..
next: even if you requested the same range, both cards have different ranges, so read the actual range property to check 😉 I guess you compare 12bit at 400mVpp and 8bit at 500mVpp (one bit ~2mV !)
but maybe the 5134 always sample at 2GS/s and mean the values while downsampling ... so RTFM 🙂
However the spec tells already
Signal to noise ratio : 5124: 58 db to 5134: 45 db , a 13db difference !!
Thank you for your reply, Henrik.
I totally agree with you about the big difference in SNR.😂
In my application, the photoacoustic signal is very small. (It gained 54 dB before going into digitizer).
So I can not use PXI 5153 for my project (the noise is over the signal).
I analyzed the noise by using FFT, and I see that the noise frequency at 5 MHz. (please see more details in the attachment)
Do you know why 5 MHz?
Thanks & Regards
5MHz noise: Also present if the input is only a 50 Ohm termination?
Since you use a preamplifier anyway , you can always add some db to get over that noise 😉
Currently, I config at 50 Ohm termination for sensor coupling (transducer, cable: 50 Ohm).
How can I add some dB in the preamplifier, Henrik?
I have no idea about getting over the noise by adding something (dB).
Can you refer me to some documents about this technique, please?