Operational Amplifier Fundamentals Unit 2 – The Inverting Amplifier
Exercise 1 – Inverting Amplifier DC Operation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to operate an inverting amplifier. You
will verify circuit operation by using a voltmeter.
EXERCISE DISCUSSION
- An inverting amplifier inverts and amplifies the input voltage.
- Output voltage is determined by: VO = -[VI x (RF/RIN)].
- The junction of RIN, RF, and the inverting terminal is the summing point of the circuit.
- The circuit input resistance equals the value of RIN since the summing junction is at virtual
ground. - A circuit is zero-base referenced because the noninverting terminal is connected to circuit
common. - Zero-based reference circuits change their output voltage polarity from plus-to-minus or
minus-to-plus as the input voltage passes through zero (circuit common). - Use Ohm’s law to determine the magnitude of electron flow through circuit parts.
- Current through the input resistor, which is connected to virtual ground at one end, is IRIN =
VI/RIN. - Feedback current (IRF) equals VRF/RF or VO/RF.
- Load current (IRL) equals VO/RL.
- When a positive input voltage is applied to the inverting input of an op amp, current flows
(electrons flow) out of the output terminal of the op amp. The value of the current is IRF +
IRL. - When a negative input voltage is applied to the inverting input of an op amp, current flows
(electrons flow) into the output terminal of the op amp. The value of the current is (IRF + IRL);
the minus sign indicates direction, not negative current.