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Design >> Analog Design >> feedback topolgy
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Message started by aman gupta on Apr 11^th, 2013, 9:49am

Title: feedback topolgy
Post by aman gupta on Apr 11^th, 2013, 9:49am

What is the feedback topology in the given circuit ??
At the input i can see that input and feedback currents are mixing, but what quantity is being sampled at the output here.
Is it voltage because i am getting If = -Vo / Rf
or is it current because i am also getting Io= -If......... ??
pls help i am confused

Title: Re: feedback topolgy
Post by raja.cedt on Apr 11^th, 2013, 12:08pm

@ o/p voltage sampling and @ input current mixing. Feedback current depends on the o/p voltage rather o/p voltage as matter of fact i donno how to define o/p current.

Thanks,
Raj.

Title: Re: feedback topolgy
Post by Vladislav D on Apr 11^th, 2013, 1:20pm

Hi,
Nothing is mixing. If case of an ideal amplifier, source current equal exactly to feedback current. Since voltage at the inverting input is a virtual ground, it is equal to DC, whatever current your apply to it i.e input impedance is zero. Consequently, input for this configuration should be a current. Voltage does not make sense, since it would be similar to connecting voltage source to ground.

Output of the amplifier is the only way for current to flow. So output voltage is defined by Rf and input current. If you apply a current source to the output you will see that this does not affect the output voltage. Therefore the output impedance is zero, i.e there is a voltage at the output.

So, this is a current input- voltage output amplifier.

Title: Re: feedback topolgy
Post by aman gupta on Apr 12^th, 2013, 3:11am

tell me what kind of feedback is there in the new figure ?

Title: Re: feedback topolgy
Post by raja.cedt on Apr 12^th, 2013, 3:31am

voltage sampling at the o/p and voltage mixing at the i/p.
please have a look into razavi basic micro-electronics.

Thanks,
Raj.

Title: Re: feedback topolgy
Post by buddypoor on Apr 25^th, 2013, 6:34am

aman gupta wrote on Apr 12^th, 2013, 3:11am:

tell me what kind of feedback is there in the new figure ?

It is "current-controlled voltage feedback".
(A clear indication of the fact that the BJT is a voltage-controlled device).

Title: Re: feedback topolgy
Post by loose-electron on Apr 26^th, 2013, 10:23am

time to buy a few textbooks!