Transcript 3404.TRF370417 Noise Floor Related Question

TRF370417 Noise Floor
Related Question
Prepared by Bill Wu
Objective
• This note is to address two questions
about TRF3704 noise floor plot taken from
a large span setting. Two cases all
showed an elevated noise floor at the
lower freq side of the carrier.
Summary
• A signal generator like E4438C could have
a noisy far-out noise floor, which leads to
the elevated noise floor at TRF3704
output.
• HP 8673E has a much cleaner far-out
noise floor than E4438C.
• A BPF filter could be used to clean the
dirty LO noise floor before sent to
TRF3704 as LO source.
Case 1 Spectrum Plot
SA noise floor, 370417 output w/ LO freq = 4, 5, and 6 GHz
Case 2 Spectrum Plot
LO Signal from
Agilent Vector
Signal Generator,
from E4438C
LO freq = 5 GHz
LO freq = 4 GHz
LO freq = 6 GHz
Observation
• Agilent E4438C showed a high noise floor
at the lower freq range. The noise floor
elevation becomes significant when the
freq is large.
E4438C, 5.7 GHz signal filtered
by a BPF, Freq = 5.3 GHz
directly sent
into Spectrum analyzer
passing through a
BPF (BW = 280 MHz)
Conclusion
• The 5.3 GHz BPF (280 MHz BW) removed
the far-out noise at the lower side of the
spectrum.
TRF3704 RF output
using Agilent
E44483C as LO,
PLO=10 dBm, BB
freq = 1 MHz
LO freq = 5 GHz
LO freq = 4 GHz
LO freq = 6 GHz
Observation
• The RF output far-out noise of TRF370417
was significant at the lower side of the RF
freq using Agilent E4438C as LO.
• The output noise was more significant for
the higher LO frequency.
RF Signal from Agilent Vector Signal
Generator E4438C, Freq = 5.3 GHz
LO directly sent
into TRF370417
LO passing through a
BPF (BW = 280 MHz)
Conclusion
• The 5.3 GHz BPF (280 MHz BW) at the
LO port cleaned the LO noise floor, which
leads to a clean output noise floor of the
TRF3704 RF output.
• High TRF3704 RF output noise was
caused by the dirty LO far-out noise floor,
not by the TRF3704 modulator.
TRF3704 RF output with
LO from HP Signal
Generator 8673E,
PLO=10 dBm, BB freq =
1 MHz
LO freq = 5 GHz
LO freq = 4 GHz
LO freq = 6 GHz
Observation
• HP Signal Generator 8673E has much
clean far-out noise floor than Agilent
E4438C.
RF output Signal using HP Signal Generator
8673E as the LO source, Freq = 5.3 GHz
LO directly sent
into TRF370417
LO passing through a
BPF (BW = 280 MHz)
Conclusion
• There is no need to use BPF to clean the
LO noise floor if HP Signal Generator
8673E was used as the LO source.