# Single balanced mixer

1. ## Single balanced mixer

I am designing a mixer RF,LO 20-25 GHz.. IF 1-3 GHz using ads.
I want to simulate the P1db compression point and the gain flatness for a constant IF.. Which frequency must i use? (20? 22.5? 25? for RF 1? 1.5? 3? for IF)
For the ideal schematic the simulation results was the same for all the range but i replace the ideal components and the simulation results are different for each frequency

2. ## Re: Single balanced mixer

I would simulate at 20 22.5 and 25, the sides are important as the centre I think. If you simulate with Periodic Steady State (PSS) analysis or transient then with higher IF the simulation should done earilier. I would use lower IF than the output IF filter's max. cut-off freq, but the highest as possible.

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3. ## Re: Single balanced mixer

You'd better to sweep RF and LO signals while one of them is fixed in order to see the real response of the Mixer.
I mean, while RF is swept (LO fixed) you will get Gain vs. RF.Then, you fix the RF, sweep LO, you'll get Gain vs. LO etc..
So, every combination will give you an insight about the Mixer.

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4. ## Re: Single balanced mixer

Big boss i do both simulations that you say but i need a constant value of IF in order to do both of them....Which value of IF should i use? And for P1db simulation which if freq and rf freq should i use?

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5. ## Re: Single balanced mixer

Originally Posted by Kooky613
Big boss i do both simulations that you say but i need a constant value of IF in order to do both of them....Which value of IF should i use? And for P1db simulation which if freq and rf freq should i use?
Try different IF Frequencies such as 1GHz, 2GHz etc.You can define HB Frequencies depending on RF and LO frequencies like
freq_IF=freq_LO-freq_RF or freq_IF=freq_LO+freq_RF...
In additional to this, P1dB Compression Point is not a proper metric for Mixers.IIP3 is generally used to characterize the non-linearity of the Mixers.

Or simply use Mixer Design Guide of ADS.There are many templates for Mixers.

6. ## Re: Single balanced mixer

Point of IF is that it is fixed because of the output IF filter. For P1db choose IF to the centre of your IF filter's frequency. If you design a sliding-IF receiver, than choose the min/max IF and simulate with both values.
The RF frequency should vary for P1db from the minimum to maximum RF values, step is arbitrary, but at least simulate with the lowest/highest RF and with the centre value.

7. ## Re: Single balanced mixer

Originally Posted by Kooky613
but i replace the ideal components and the simulation results are different for each frequency
In this situation I recommend to spend some time designing (and tuning) the LO, IF, and RF ports matching networks. This should be done for a wide range of frequencies.

8. ## Re: Single balanced mixer

vfone the s parameters simulations show less than -10 db at all the range of three ports but i use harmonic balance simulation for the gain and from 20 to 23.5 Ghz i see the gain flatness i had in the ideal schematic...but from 23.5 to 25 Ghz the gain shows a sharp drop and i can not find the reason

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9. ## Re: Single balanced mixer

Originally Posted by Kooky613
vfone the s parameters simulations show less than -10 db at all the range of three ports but i use harmonic balance simulation for the gain and from 20 to 23.5 Ghz i see the gain flatness i had in the ideal schematic...but from 23.5 to 25 Ghz the gain shows a sharp drop and i can not find the reason
S-parameters do NOT characterize the Mixers.

10. ## Re: Single balanced mixer

I use it only for matching

11. ## Re: Single balanced mixer

Impedance matching for mixer ports, it is a complex task.
Is not enough to provide good impedance match for fundamental of RF, LO, IF, or image frequency, but also should provide short or good load impedance for harmonics of their frequencies.
You have to spend some time reading the theory:
http://www.rfcafe.com/references/art...tems_part2.pdf

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