2. Using an op-amp

An op-amp has a high gain as shown in Figure 2-1. The gain is dependent on frequency. The gain also varies from device to device and is affected by temperature and other environmental conditions. Therefore, op-amps are generally used with negative feedback. Depending on conditions, negative feedback turns into positive feedback, causing the feedback loop to oscillate abnormally.
Section 2 describes feedback oscillation, basic amplifier circuits using an op-amp, a virtual short-circuit required when considering an amplifier circuit.

1. Feedback (positive and negative feedback)
2. Open-loop gain and closed-loop gain
3. Oscillation
4. Basic amplifier circuits
5. Virtual short-circuit (virtual ground)