Quick question re. 1dB compression of an RF mixer

[wheels1888]

I am quite inexperienced with actually using mixers, so when I was bombarded with specifications by a data sheet I was a bit intimidated at first. I think I have learned what most of the metrics mean thanks to a great deal of resources available online. I just have one question.

The data sheet for the mixer I am going to use lists the 1 dB compression as "1 dB Compression (Output)". Most everywhere else I see it as defined with regards to the RF input. To convert back from this "output compression" (if I am understanding this correctly) do I need to simply subtract the conversion gain from the compression point?

If I am leaving out information please let me know. Also, if you would like to take a look at the data sheet, here it is: http://www.hittite.com/content/documents/data_sheet/hmc621lp4.pdf

 

[yungman]

I think so if I understand what you mean. Like if you have a gain of +10, if your input is 0.5V, your output read 5V. If you increase the input to 1V and you observe the output is only 9V. So you loss 10% of the signal. from my memory, 1dB compression is about loss of 10%. So 1V is your "input 1dB compression point". You can work back from the output to the input. Say if the output 1dB compression is at 0dBm, and if the conversion gain is 6dB, then your input 1dB compression point should be -6dBm.

That is from my memory, verify this. Numbers might be wrong, the idea should be correct.

 

[wheels1888]

I think so if I understand what you mean. Like if you have a gain of +10, if your input is 0.5V, your output read 5V. If you increase the input to 1V and you observe the output is only 9V. So you loss 10% of the signal. from my memory, 1dB compression is about loss of 10%. So 1V is your "input 1dB compression point". You can work back from the output to the input. Say if the output 1dB compression is at 0dBm, and if the conversion gain is 6dB, then your input 1dB compression point should be -6dBm.

That is from my memory, verify this. Numbers might be wrong, the idea should be correct.

Yes that is exactly my logic. Thanks for the input! So, in the case of the mixer I am using where,

1 dB compression (output) = 19 dBm
Conversion gain = 27 dB

Then,

1 dB compression (input) = 19 dBm - 27 dB = -8 dBm

Does this seem correct? The LO drive is designed to range from -3 to 3 dBm, so the difference between it and the 1 dB compression seem reasonable, at least from what I've read.

 

[yungman]

Wait, if the output compression point is 19dBm, conversion gain is 27dB, then the input 1db compression should be 19+1-27=-7dBm. Remember the output is 1dB compression, so ideally the output should be 20dBm if there is no compression. Now you got me confused!

I don't follow your LO part.

 

[wheels1888]

Oh, right! Sorry, you are definitely correct. I'm mixing up the output and input compressions... Ugh. I think why it was defined as such is because there are a few integrated amplifiers in the mixer.

Haha, and don't worry! From what I've read there is a "typical" value for the difference between LO drive and input compression. I was just using this difference to rationalize the value of input compression.

Thanks so much for all the help though!