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Design >> RF Design >> Mixer Output Impedance
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Message started by hrkhari on Feb 4^th, 2005, 9:32pm

Title: Mixer Output Impedance
Post by hrkhari on Feb 4^th, 2005, 9:32pm

Hai Guys:

Currently I am working on the design of DSB mixer, I would appreciate if you could kindly help me out in resolving some arising issues, as below:

1. What shall the output termination resistance range be applied to the output port?. I find that higher settings of resistance value highly improves the Conversion Gain.

2. What is the significance of obtaining the OIP3 and Output 1dB compression point compared to IIP3 and input 1dB compression point in an active circuit topology?.

Thanks in advance

Rgds

Title: Re: Mixer Output Impedance
Post by fab_jor on Feb 9^th, 2006, 10:58pm

I have the same questions and more: Output impedance has a capacitive part. So, can I drive a pure resistive load without problems ? And about the conversion gain ? It´s gets worse ?

regards

Title: Re: Mixer Output Impedance
Post by ACWWong on Feb 13^th, 2006, 3:07pm

1. the output termination resistance or load impedance should represent the input impedance of the following stage. Only by doing this does the conversion gain of the mixer mean anything once placed into a system.

2. the OIP3 will only equal the IIP3 (obviously differnec of the conversion gain included) if the output doesn't signal limit. Often, because of the gain and limited output headroom, one find the output clipping at much lower signal levels than one expect from the input stage (gm stage is classical gilbert) linearity alone.

wrt the output impedance capacitive part... this will limit the conversion gain bandwidth... ie the IF bandwidth for which you get the conversion gain will reduce with more load capacitance.