IIP3 @ 10MHz offset for WCDMA

[boshiouke]

The inband IIP3 for WCDMA is specified @ 10MHz offset. So I ran a 2-tone test w/ following parameters,

RF1=2150MHz
RF2=2160MHz
LO=2140MHz

First of all, should I have used the 2 tones @ 10/20.5MHz so that IM3(0.5MHz) falls within the BW(5MHz)?

Secondly, due the LPF @ mixer output w/ cutoff of 8MHz, the output @ 10MHz is much bigger than @ 20MHz. In this case, how do I calculate IIP3? Does "Pin+1/2 x (delta between fundamental and IM3)" still apply? Which 2 frequencies should I take the delta from? Assuming the Pin is in linear region of the mixer.

Thank you so much.

 

[vfone]

Receiver IIP3 is:
IIP3(dBm) = 2tone_lev(dBm) + [2tone_lev(dBm) – RX_lev(dBm) + S/N(dB) ] / 2
where:
2tone_lev = Two-tone intermodulation level in dBm (WCDMA spec requirement is –46dBm @ +/-10MHz and +/-20MHz from the receive frequency)
RX_lev = Receiver desired input level (RX sensitivity + 3dB)
S/N = Analog Signal to Noise Ratio (~9dB)

 

[boshiouke]

I appreciate your input, Vfone. But I'm aware of the info you posted from a WCDMA system article from Microwave Journal. What I want to know is how to relate that to the numbers I have, as indicated in my posting. Thank you.

 

[vfone]

First of all I don’t know what MWJ article you are talking about. This is a standard RF systems formula.
Second, you have to follow the WCDMA spec for levels, spacing, etc.
Third, seems that you are looking to calculate the LNA IIP3 not Receiver IIP3. They are different things.

 

[boshiouke]

Again, I appreciate your attention, Vfone. Here's the link to the article I was talking about.
**broken link removed**

If the link doesn't work, simply go to www.mwjournal.com and search for w-cdma in Feb. 2000 issue. It talks about how to derive IP3 for the ENTIRE Rx, not only mixer.

But, what I'm asking is for mixer ONLY, specifically during simulation of a 2-tone test. As indicated in Razavi's book, I do know the "quick way" to calculate IIP3. But my case is kind of different.

Thank you.