Operational Amplifiers (Op-Amps)

Owned by Kevin Li
Last updated: 2022-06-18 by Jennifer Yun
3 min read

  • What is an opamp? How does it work? - comeback

    • Operational amplifier (Opamp) is an integrated circuit that can amplify weak input signals.

    • It is a voltage amplifying device.

    • It is used in signal conditioning, filtering, or to perform mathematical operations such as add, subtract, integration, and differentiation.

  • What does an op-amp look like? What are the two input terminals?

    • The op-amp has two input terminals and one output terminal.

    • One of the input terminals is called “inverting input” and is marked with a negative sign (-). The other input terminal is called “non-inverting input” and is marked with a positive sign (+).

  • What are the three rules of an ideal opamp?

    • There are three rules for an ideal opamp.

      • First, the open-loop gain must be infinite.

        The open-loop gain represents the gain of the opamp without positive or negative feedback. This helps the opamp to amplify the input signal better.

      • Also, the two input terminals don’t draw any current.

        This rule came from the characteristic of input impedance. The input impedance must be infinite, and since the impedance is voltage over current, the input current must be 0.

      • Lastly, with negative feedback, the potential difference between two input terminals should be zero.

        This stabilizes the opamp’s characteristics. Also, with negative feedback, the gain of the opamp can be controlled and calculated.

  • How does an open-loop op-amp behave? What type of circuit is it? Describe it

  • What is the difference between open-loop and closed-loop control? What about negative feedback and positive feedback control?

 

 

  • What does an inverting and non-inverting op-amp circuit look like? What are their voltage gains? - comeback

    • Non-inverting op-amp circuit: This is a circuit for amplifying and outputting input signals.

    • Inverting op-amp circuit: In this case, if the input voltage increases, then the output voltage decreases.

 

 

 

 

  • What is a difference amplifier? What is its voltage gain?

    • This circuit amplifies and outputs the voltage difference of two input voltages.

  • What is an instrumentation amplifier?

  • What are the differences between a difference amplifier and an instrumentation amplifier? When would you choose to use one over the other?

  • What is the DC gain of an ompamp?

  • What is common-mode and differential gain? What are their ideal values?

  • What is the gain-bandwidth product?

  • What determines slew rate and rise/fall time?

  • Pros/cons of fast/slow slew rates?

  • Why are BJTs more often used for amplifiers than MOSFETs?