Question asked by TPiggin on Nov 21, 2013
Latest reply on Dec 5, 2013 by Qui

Hi Qui, I know I have asked about this topic before, but after recently reviewing it I'm not sure what I implemented was correct...

Referencing the document you wrote titled voltage gain vs power gain for demodulators July 10 2012 i have a few queries...

On P.2 under point C: you calculate the power delivered to the 450R load based on an I+-I- differential voltage measurement, but you use 500R in the calc. I realise you've done this because you've included the 2x25R internal resistors, but is this correct? Does the voltage gain of the device include the 25R resistors? I'm confused because you say the 450R comes from the 50R spectrum analyser load translated across the 9:1 transformer, but the spectrum analyser is not measuring the power dissipated in the 25R legs, only the power dissipated in the translated 450R load.

I'm thinking its possibly better for me to work in voltage as this is obviously what my ADC is measuring, which in that case means working out the voltage gain at my frequency and for a given load. We can then convert back from output voltage to demod input voltage and work out the power there as we know the input is 50R. Does this work? What is the calculation? I know from the datasheet that at 900MHz the voltage gain is 3dB for a 200R load, what if my frequency range is 1600-2200MHz? with a TBD load? e.g. could be 300, 400, 500 etc. we could increase the load if we need a higher voltage swing...

Sorry for all the questions

Thanks

Tom