font meeting1 digital signal filtering n. blaskovic
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FONT Meeting 1
Digital signal filtering
N. Blaskovic
N. Blaskovic
Contents
• Fourier transforms of I and Q waveforms without BPF and with 714 MHz & C-band BPFs
• Digital LPF tests and application to data without BPFs
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Fourier transforms
• Waveforms and their Fourier transforms:– Without BPF (12 June)– With 714 MHz BPF on dipole signal (12 June)– With C-band BPF on dipole signal (19 June)
• New:– Pedestal subtracted– FFT of all usable samples (184 samples)
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IPA
IIP
A Q
no BPF
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IPA
IIP
A Q
714 MHz BPF
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IPA
IIP
A Q
C-band BPF
Digital filtering
• Use a 6th order low pass Butterworth filter• Cut-off frequency: 25 MHz• Sampling frequency: 238 MHz (SIS)
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25 MHz 119 MHz
25 MHz 119 MHz
Digital filtering
• Test 25 MHz digital LPF with signals:– A: sine waveform with 9.5 MHz frequency– B: sine waveform with 47.6 MHz frequency– C: sum of A and B
• Filtered signals are denoted Af, Bf & Cf, respectively
• Phase lag of filtered signals observed relative to unfiltered signals
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Digital filtering
• Digital LPF applied to data without BPFs:– 10 MHz LPF
(corresponding to 714 MHz BPF bandwidth)– 25 MHz LPF
(corresponding to C-band BPF bandwidth (?))
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IPA
IIP
A Q
no digital LPF
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IPA
IIP
A Q
10 MHz LPF
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IPA
IIP
A Q
25 MHz LPF
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Appendix
Waveforms and their Fourier transforms for IPB and IPC with different BPFs and 10 & 25 MHz digital LPFs without BPF
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IPB
IIP
B Q
no BPF
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IPB
IIP
B Q
714 MHz BPF
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IPB
IIP
B Q
C-band BPF
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IPB
IIP
B Q
10 MHz LPF
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IPB
IIP
B Q
25 MHz LPF
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IPC
IIP
C Q
no BPF
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IPC
IIP
C Q
714 MHz BPF
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IPC
IIP
C Q
C-band BPF
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IPC
IIP
C Q
10 MHz LPF
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IPC
IIP
C Q
25 MHz LPF
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