power limitations for m79hx mixer

[yefj]

Hello ,there is a component as shown below,in which it could be used as phased detector as shown in the data sheet below.
based on the data sheet , i put my inputs at LO and RF inputs and IF is my phase detector (DC) output.
on one hand they say that maximal input power is 21dBm
on the other table they say that we have an IP3 compression at 0dB.
I am confused.
What is the proper input power for this mixer used as a phased detector?

What is the the meaning of "mixed could be used as phase detector because IF port DC coupled to diode"?
for me coupling is sort of power dividing.What is the physical meaning of IF DC coupled to diode?

https://cdn.macom.com/datasheets/M79H_M79HC.pdf

 

[G4BCH]

on one hand they say that maximal input power is 21dBm

Yes.

on the other table they say that we have an IP3 compression at 0dB.

No. This is one of the conditions under which the IP3 was measured. 2 signals at nominal 13GHz at 0dBm each at the RF input.
1dB compression is +15dBm input with LO input power of 20dBm.
These levels should be OK for use as a phase detector. So long as you do not exceed the total maximum input power (that is RF + LO) the levels are not too critical. The greater the RF input the greater the DC IF output.

DC coupling means that the IF output is directly connected to the mixer diode there is no capacitor or transformer coupling. Look at the circuit diagram of a diode double balanced mixer, it should be obvious from that. DC coupling is a commonly used term.

 

[yefj]

Hello,i am trying to use this mixer shown bellow. I have tried to down convert from 10GHz to 3 GHz. So i put on RF 10Ghz LO 7GHZ both on input power of -10dBm. the result was that it didnt work. I think maybe my LO power if too low and the LO frquency is too large. There is a table shown bellow. How can i see from the data sheet what is the proper power for LO and proper LO frequency? Thanks.

 

[vfone]

In the datasheet is mentioned very clear: "LO DRIVE: +20 dBm (NOMINAL)"

 

[G4BCH]

This is a high level mixer, it needs at least +10dBm to work at all, and then its performance will be poor. All diode double balanced mixers need enough power to be able to fully turn on the diodes. In a low level mixer this is two diode junctions in series, in these high level mixers it can be 4 or 6 junctions, sometimes with series resistance as well.
There may be thermal problems with using a high level mixer as a phase detector., it depends on the accuracy you need. I have in the past used +23dBm LO mixers in an IQ detector and that was quite problematic to compensate over a wide temperature range.

 

[yefj]

so what did you do to handle the heat problem of the mixer?
Thanks.

 

[G4BCH]

Measure the drift over the operating temperature range and then feed an opposing temperature varying current into the mixers. We got to about +/-250uV over -45 to +85, but it took some time to get it right. Each unit had ot be individually compensated. This was in the days when high speed DSP was a few MSPS.