opamp input impedance

[p11]

why input impedance of non inverting amplifier is more than inverting amplifier ??

 

[KlausST]

Hi,

because in noninverting configuration the voltage on IN+ folows the input voltage without (much) current.

In inverting configuration the voltage on IN- is constant, therefore the input impedance is determined by the input resistor.

(This is for the complete circuit. but for sure both inputs of an OPAMP seen without external circuit are high impedance)

Hope this helps.

Klaus

 

[Borber]

What operational amplifier? You mean inverting and noninverting inputs.
Current feedback operational amplifiers has genericaly different input impedances(as you are questioning) as oposed to voltage feedback operational amplifiers which has equal input impedances.

 

[LvW]

why input impedance of non inverting amplifier is more than inverting amplifier ??

From the system point of view the answer is:

* Voltage feedback always increases the input impedance (example: non-inv. opamp),
* Current feedback always decreases the input impedance (example: inv. opamp).

 

[crutschow]

In the non-inverting amp configuration the input goes directly to the op amp (+) input which is normally very high impedance.

In the inverting amp configuration the input goes through the input resistor to the virtual ground point at the (-) input so the input impedance is equal the the input resistor value. That is almost always less than the (+) op amp input impedance.