Although there are many types of amplifiers, different amplifiers are suitable for interfacing with different types of sensors, but most complex amplifiers are built by combining operational amplifiers.

In almost cases today, op amps are configured in different ways using a feedback network to “calculate” the input signal. There are 20 formulas used to calculate.

**Figure 1. Voltage Follower**

Note: Buffer High Impedance Signal and Low Impedance Load

**Figure 2. In-phase Op Amp**

Note: In-phase Signal Amplification

**Figure 3. Reversed-phase Op Amp**

Note: Amplify and Invert Input

**Figure 4. Voltage Subtractor, Differential Amplifier**

Note: Amplify the voltage difference and suppress the common - mode voltage

**Figure 5. Voltage Adder**

Note: Summation of Adding Voltage Values

**Figure 6. Low-pass Filter, Integrator**

Note: Limit Signal Bandwidth

**Figure 7. High-pass Filter, Differentiator**

Note: Eliminate DC, Amplify AC Signal

**Figure 8. Differential Amplifier**

Note: Drive Differential Signal to Analog-to-Digital Converter From A Differential or Single-ended Signal Source

**Figure 9. Instrumentation Amplifier**

Note: Amplify the Low Level Difference Signal and Suppress the Common Mode Signal

**Figure 10. Single State Op Amp Noise**

Note: RTO NOISE=NG×RTI NOISE

RTI=Converted to the Input

RTO=Converted to the Output

**Decibel Formula (equivalent impedance)**

**Johnson-Nyquist Noise Formula**

**Ohm's Law (DC circuit)**

**Figure 11. Closed-loop Frequency Response (voltage feedback amplifier)**

**Resistance Formulas**

**Reactance Formulas**

**Transformer (step-up or step-down ratio)**

**Impedance Formulas (in series)**

Note: RL in series

RC in series

LC in series

RLC in series

**Voltage and Impedance Formulas (parallel connection)**

## 3 comments

Add something, the op amp can be simply viewed as a high-gain direct-coupled voltage amplifying unit with one signal output port, a non-inverting input, and an inverting put, which belong to high-impedance inputs. So non-inverting amps, inverting amps, and differential amps can be made based on these amplifying units.

We should know the principle before calculations, the power supply mode of the op amp is divided into dual power supply and single power supply. For dual-supply op amps, the output can be varied across zero voltage and the output can be set to zero when the differential input voltage is zero. With a single-supply op amp, the output varies over a range of power and ground.

The output signal of the operational amplifier is proportional to the difference between the signal voltages of the two inputs. In the audio segment: output voltage = A0 (E1-E2), where A0 is the low-frequency open-loop gain , E1 is the input signal voltage of the non-inverting terminal, and E2 is the input signal voltage of the inverting terminal.