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ac coupling and then dc biasing with resistor

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sharkies

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I'm trying to ac couple then dc bias with a resistor.
An example will be mixer a input where you ac couple the LNA output and then bias it with a resistor.
For some reason it's not working, I'm using C=100p, R=1G which are really big values...
Am I doing something wrong?
 

IanP

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R=1G is really big, try something more realistic, say, 1M ..
As far as the capacitance value is concerned, it depends on the frequency of the AC signal that you intend to pass through it ..
Without going into details, it’s impedance calculated for the lowest frequency(1/ωC) should be low, I’d say below 10ohms, but that depends on other components around it ..

Rgds,
IanP
 

sharkies

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I got it solved,,, I had two coupling caps connected together.. one from the output of the previous block, and one from the input of the following block. Sorry for my stupidity.
Still question though, what's the usual resistance value used for the biasing? 1M still seems really big. Also, should the bottom plate of the coupling cap be facing towards the input, or the other way around?
or does it matter?

Added after 15 minutes:

also, my entire signals are attenuated,
If I used large RC values this shouldn't be happening right?

Added after 29 minutes:

I'm guessing that there's an impedance matching problem? I'm ac coupling a divider output to an amplifier with LC load. How do I fix the input signal attenuation problem?
 

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