Sampling frequency vs the signal frequency

[aviaashu]

Friends,

My signal from a analogue photomultiplier tube has to be fed in a transimpedance amplifier before it is read by the NI daq card (6353 X series in my case). This is because the PMT output is current output and i need to convert it in a readable voltage. Now the signal and preamplifier frequency is 80 Mhz (same to that of excitation laser pulse). Does the sampling rate of a NI DAQ  (typically  less than 5MHz) and the preamplifier frequency need to be same or this frequency mismatch will not have any effect on data acquistion. 

Avinash

[Henrik_Volkers]

The max sampling rate for one channel is 1.25MHz and for more CH 1MHz.

The max bandwidth of your system is 80MHz ...but you need to restrict your bandwith to <600(<500)kHz.  I'm not a PMT expert 😉  but I know that in the times of 'slow' aquisition systems  a defined low pass (pulse shaping) filter was used to capture energy spectra.

Your laser pulses with 80Mhz?  To measure  pulse caracteristics about 20 times higher bandwidth is needed.. (Jim Williams from linear wrote some notes on that in an app note)  a 2GHz sampler  would be nice .. DigiScope?

Or do you 'simply' need some sort of mean energy received value?

[aviaashu]

Henrik,

Thanks for the response.

We are not interested in the pulse shape of the signal. We are just interested in mean value for imaging. We will be using the PMT for imaging a sample in a pixel by pixel manner. Datta at each pixel is recorded and finally a image is stitched. I want to know if we need a preamplifier matching with signal frequency or preamplifier matching with the DAQ frequency.

If you go to experimental section of attached manuscript ,they have used a preamplifier with max frequency of 1.5 MHz, with a 80mHz laser. Correct me if I understood wrong. The data in this paper was collected by an S-series DAQ. 

Avinash  

[Henrik_Volkers]

Well, first I would try to look at the signal with a oscilloscope (Do you have access to one?) Nice would be one with about 100MHz bandwidth... but an (old) analog one with 50MHz also should work (the old analog ones can usually show signal higher than the claimed bandwidth;))

Now you need to integrate the output signal (mean it) .. I asssume that the TIA signal output has a 50 Ohm impedance.  I would try a simple RC filter/integrator in the 300kHz range ..

So use a 50 Ohm BNC cable from the TIA to your filter box (close to the DAQ) .

The metal box has an BNC input (via cable to the TIA) and a BNC output (with a short BNC cable to the DAQ ) 

In the box the BNC shields are connected (GND) . From input pin to GND use two 100 SMD resistors or one 51 Ohm resistor to GND (termination) .  From input to output one 1k Ohm resistor and from output pin to GND a 470pF ceramic or foil capacitor.