Revision as of 11:28, 11 January 2010

Ideal Op Amp Characteristics

Infinite input impedance
Infinite open-loop gain for the differential signal
Zero gain for the common mode signal
- You can easily change an differential amplifier into a common-mode amplifier by grounding one of the inputs
Zero output impedance
Infinite bandwidth
- To allow for infinite gain regardless of the frequency?

No current flows into the + or - terminals
If negative feedback is present (and no positive feedback), then $V_{+}=V_{-}\,$
Write nodal equations at $V_{+}\,$ $V_{+}\,$ and $V_{-}\,$ $V_{-}\,$ , but not at $V_{o}\,$ $V_{o}\,$
- There is a voltage source inside the op amp. Writing a nodal equation at a voltage source adds an extra equation and an extra variable. You gain no ground.

@@ Line 9: / Line 9: @@
 =Op Amp Nodal Analysis=
-*No current flows into the + or - terminals
+*[[Chapter_1#Amplifier_Models | No current flows into the + or - terminals]]
 *If negative feedback is present (and no positive feedback), then <math>V_+ = V_-\,</math>
 *Write nodal equations at <math>V_+\,</math> and <math>V_-\,</math>, but not at <math>V_o\,</math>
+**There is a voltage source inside the op amp. Writing a nodal equation at a voltage source adds an extra equation and an extra variable. You gain no ground.