Try this:
A = dlmread('F0000CH1.csv',",",0,3);
Time = 1e9.*A(:,1);
Voltage = A(:,2);
figure
plot(Time,Voltage,'LineWidth',2)
title('Time Domain Function')
ylabel('Voltage (V)')
xlabel('Time (ns)')
xlim([-125 400])
ylim([-4.5 6])
L = numel(Time); % Signal Length
Ts = mean(diff(Time)); % Sampling Interval
Fs = 1/Ts; % Sampling Frequency
Fn = Fs/2; % Nyquist Frequency
FT_V = fft(Voltage)/L; % Normalised Fourier Transform
Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector
Iv = 1:numel(Fv); % Index Vector
figure
plot(Fv, abs(FT_V(Iv))*2)
grid
xlim([0 0.5])
Wp = 0.045; % Passband Frequency (Normalised)
Ws = 0.050; % Stopband Frequency (Normalised)
Rp = 1; % Passband Ripple
Rs = 50; % Passband Ripple (Attenuation)
[n,Wp] = ellipord(Wp,Ws,Rp,Rs); % Elliptic Order Calculation
[z,p,k] = ellip(n,Rp,Rs,Wp); % Elliptic Filter Design: Zero-Pole-Gain
[sos,g] = zp2sos(z,p,k); % Second-Order Section For Stability
figure
freqz(sos, 2^16, Fs) % Filter Bode Plot
Voltage_filt = filtfilt(sos, g, Voltage); % Filter Signal
figure
plot(Time,Voltage_filt,'LineWidth',2)
title('Time Domain Function')
ylabel('Voltage (V)')
xlabel('Time (ns)')
xlim([-125 400])
ylim([-4.5 6])
I chose a passband frequency of 0.045 Hz and a stopband frequency of 0.050 Hz, based on the Fourier transform results, since it appeared to give good results. This code designs an 7-order elliptic filter, since these filters are efficient. Experiment with the filter characteristics to decide on the paramerers for your hardware filter.
