Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Cascaded Phase Noise Calculation

Not open for further replies.


Junior Member level 3
Nov 9, 2008
Reaction score
Trophy points
Activity points
I am trying to find articles and/or books that would explain how to assign phase noise in an RF downcoverter given a system level requirement. I would also like to know how to determine the reference phase noise of the synthesizer based on its output requirement. So far I have ran into papers that have closed form equations which require parameters that are very hard to find. The idea would be to have the equivalent of noise figure cascade analysis but with phase noise.

Thanks in advance.

Thanks for your reply. I happen to have already read both of those papers. They gave me guidance as far how to determine phase noise for different components and how to treat correlated and uncorrelated signals. However, I need to understand how to "add" the contribution in the RF and LO paths of a downcorveter so that I can determine the phase noise at the output of the IF chain. The other limitation I have is that I don't have any phase noise data for the signal at the RF port and I am trying to find out if there are a good numbers to use depending on the application.

Because phase noise is actually a power level at a specific distance from the carrier, combining two signals, the phase noise result will be a summ of both phase noise levels.
For example, combining two signals having both the absolute value of the phase noise of -100dBm/Hz at 10kHz from their carriers, will result a signal having an absolute phase noise level of -97dBm/Hz at 10kHz from the carrier (3dB higher, or double the power).

The LO phase noise (or the PLL) is the greatest contributor to the phase noise of a system.
For example phase noise added by a diode mixer or by an IF amplifier is negligible compared to a PLL or LO phase noise. Here, doing the analysis, don't have to confuse phase noise with noise figure.

If the RF input is strong, its phase noise may be also a contributor to the receiver system phase noise. This is the reason when doing receiver blocking tests (strong interfere at RX input), the signal generator used for blocking signal should have very low phase noise, usually at least 10dB lower than the receiver system phase noise.

Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to