Ozzie’s Rule
"If an op-amp input has only a single impedance connected to it, this impedance can be replaced with a short without affecting circuit gains."
Ozzie’s rule identifies components that do not affect circuit gains. Before removing the components, make sure that they are not needed to meet balance constraints or for test isolation.
Reduction is not recommended for Bipolar Input Amplifiers with High Impedances.
The K9 Design Procedure adds input resistors and a feedback resistor. Ozzie’s Rule identifies resistors that can be removed. Consider the Buffer Amplifier shown below:
Buffer Amplifier
In this case the
input resistor. R1, and the feedback resistor, RF, can be replaced with shorts.
The reduced circuit is shown below.
Other circuits that can be reduced are:
- Inverting Amplifiers with one or more inputs.
- Single input non-inverting amplifiers
Use Ozzie’s Rule with caution. Removing a resistor will affect the testability and increase bias current error.