how to simulate 1db comprassion point of a mixer on ADS

i am designing a mixer using MOS Gilbert cell... i am trying to show the 1 db compression point by plotting IF ideal power with IF actual verses RF power but i dnt knw how to get the IF ideal power.. can any one help.. thanks

If you can plot IF Power (out) vs RF Power (in) then that should be enough. Best done as a swept simulation. At lower input power levels the response should be linear so 1dB extra input RF Power gives 1dB extra IF Power. Imagine that line extending on infinitely. Then at higher input power levels the output power level should start to drop below that line. Find the point where the difference is 1dB will indicate the 1dB compression point referred to either the input power (x axis) or the output power (y axis) as required.

Plotting (IF Power - RF Power) vs RF Power and look for 1dB roll-off would give the same measurement. This will give you the gain at 1dB compression or input RF Power at 1dB compression again.

Aytan said:

i am designing a mixer using MOS Gilbert cell... i am trying to show the 1 db compression point by plotting IF ideal power with IF actual verses RF power but i dnt knw how to get the IF ideal power.. can any one help.. thanks

Click to expand...

If you know the linear gain of the mixer, you could add a P_1tone source, an amplifier component, and a 50 ohm load. Set the input power of the amp circuit to match the input power of the source driving the mixer (both circuits start with the same input power, i.e. use a variable for the input power value and sweep it). Plot Pin vs. Pout for the two circuits. The amplifier should give you a linear gain for a much wider power range than the mixer. You should be able to see the mixer compressing while the amplifier circuit continues to show a linear response. Plot both lines on the same graph, and use a delta marker to show where the difference is 1 dB.

thanks a lot for your replies RealAEl and enjunear... they are extremely helpful... may i ask another question... how also to plot the IMD and third order intercept... i am a beginner on ads so i am still learning the tool... thank you again for your help

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enjunear.. how can i find the linear gain...

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would some one please tell me hoe to test the IMD and the third order intercept point and NF for a diff. Gilbert cell mixer detailed steps in ads as i am a beginner and i dont knw how to preform these tests on ads... thanks

To determine the linear gain of your device, drive a low-level signal into it and measure the output power. It's just gain... it's called the linear gain because you test it when your device is performing in a linear fashion (e.g. not in compression). Plot a Pin vs. Pout sweep. Where the slope of the line is constant is your region of linear operation... Pout - Pin = gain. Use that gain value in the amplifier circuit I mentioned previously. That should give you a linear Pin/Pout trace that matches up with the Pin/Pout trace of your mixer (until the mixer begins to compress).

For testing IMD in amps, a commonly used technique is two-tone testing (to get TOI, Third Order Intercept point). I haven't dealt much with mixers, but there's got to be something similar. Hit google and find some articles regarding IMD testing mixers.
For amps: Two-tone IMD measurement techniques

As for Noise Figure, open up a new project in ADS. In the "create new project" dialog box, look in the drop-down menu for templates. In there you'll find some relating to Noise Figure (NF). See if any of those give you a clue on where to start/setup your system.