SLOA011B January   2018  – July 2021 LF347 , LF353 , LM348 , MC1458 , TL022 , TL061 , TL062 , TL071 , TL072 , UA741

 

  1. 1Introduction
    1. 1.1 Amplifier Basics
    2. 1.2 Ideal Op Amp Model
  2. 2Non-Inverting Amplifier
    1. 2.1 Closed Loop Concepts and Simplifications
  3. 3Inverting Amplifier
    1. 3.1 Closed Loop Concepts and Simplifications
  4. 4Simplified Op Amp Circuit Diagram
    1. 4.1 Input Stage
    2. 4.2 Second Stage
    3. 4.3 Output Stage
  5. 5Op Amp Specifications
    1. 5.1  Absolute Maximum Ratings and Recommended Operating Condition
    2. 5.2  Input Offset Voltage
    3. 5.3  Input Current
    4. 5.4  Input Common Mode Voltage Range
    5. 5.5  Differential Input Voltage Range
    6. 5.6  Maximum Output Voltage Swing
    7. 5.7  Large Signal Differential Voltage Amplification
    8. 5.8  Input Parasitic Elements
      1. 5.8.1 Input Capacitance
      2. 5.8.2 Input Resistance
    9. 5.9  Output Impedance
    10. 5.10 Common-Mode Rejection Ratio
    11. 5.11 Supply Voltage Rejection Ratio
    12. 5.12 Supply Current
    13. 5.13 Slew Rate at Unity Gain
    14. 5.14 Equivalent Input Noise
    15. 5.15 Total Harmonic Distortion Plus Noise
    16. 5.16 Unity-Gain Bandwidth and Phase Margin
    17. 5.17 Settling Time
  6. 6References
  7. 7Glossary
  8. 8Revision History

3 Inverting Amplifier

Figure 3-1 shows another useful basic op amp circuit, the inverting amplifier. The triangular gain block symbol is again used to represent an ideal op amp. The input terminal, + (Vp), is called the non-inverting input, whereas – (Vn) marks the inverting input. It is similar to the non-inverting circuit shown in Figure 2-1 except that now the signal is applied to the inverting terminal via R1 and the non-inverting terminal is grounded.

GUID-E1221B4F-7E20-4004-B4AD-A6EC146FB95A-low.gif Figure 3-1 Inverting Amplifier

To understand this circuit, we must derive a relationship between the input voltage, Vi and the output voltage, Vo.

Since Vp is tied to ground,

Equation 21. Vp = 0

Remembering that there is no current into the input, the voltage at Vn can be found using superposition. First let Vo = 0,

Equation 22. GUID-680E86C4-D5D4-4D8C-8D3A-D448924537C9-low.gif

Next let Vi = 0,

Equation 23. GUID-BCF4CC89-E9E1-4AA4-ADA3-36FB6795E16F-low.gif

Combining

Equation 24. GUID-3D7E5F7E-3E07-4A53-BBAA-F2C5BADF7F0F-low.gif

Remembering equation Equation 14, Vo = aVd = a(Vp - Vn), substituting and rearranging,

Equation 25. GUID-B880F66E-331D-488C-A52E-0C1BA03DB495-low.gif

where

Equation 26. GUID-B0C4054F-C3C0-4783-A0EF-C83DA2D0624A-low.gif

Again we have an amplifier circuit. Because b ≤ 1, the closed loop gain, A, is negative, and the polarity of Vo will be opposite to Vi. Therefore, this is an inverting amplifier.