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 PlotSA 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 = 4 GHz

LO freq = 5 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

passing through a BPF (BW = 280 MHz)

directly sent into Spectrum analyzer

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 = 4 GHz

LO freq = 5 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 passing through a BPF (BW = 280 MHz)LO directly sent

into TRF370417

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 = 4 GHz

LO freq = 5 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 passing through a BPF (BW = 280 MHz)LO directly sent

into TRF370417

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.