help ! how to calculate??????????

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
bogdan_borko

bogdan_borko

Member
Joined 2005
how to calculate output impedance of these amp stages?
 

Attachments

  • amp-stages.jpg
    amp-stages.jpg
    15.9 KB · Views: 186
I

ilimzn

Member
Joined 2005
Re: Re: help ! how to calculate??????????

Tube_Dude said:
Amp stage A - the output impedance is the value of R4 in parallel with R5
Amp stage B - 1/Gm ( Gm is the transconductance of the mosfet ) in parallel with R9 and R6.
Click to expand...

Actually, assuming R5 in amp A and R6 in amp B are the load, then what you have written is the total load the amp sees, not it's output impedance (this does not include the load). So, for amp A it would be R4, because a MOSFET is a voltage controlled current source, and current sources have very high impedance (ideally infinite), and in amp B it is 1/gm of the MOSFET at the chosen operating point in parallel with R9.
 
Tube_Dude

Tube_Dude

Member
Joined 2002
Re: Re: Re: help ! how to calculate??????????

ilimzn said:


Actually, assuming R5 in amp A and R6 in amp B are the load, then what you have written is the total load the amp sees, not it's output impedance (this does not include the load).
Click to expand...


Hi ilimzn

But if you assume that R5 and R6 are the DC current path for charging the capacitors C2/C4 and part of the design , the output impedance is calculated as I have said.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom