Operational Amplifier Key Terms

This glossary collects op amp terms and specifications to provide a handy reference guide for designers. This article describes op amp parameters listed in the Electrical Characteristics table of an operational amplifier (op amp) data sheet.

1. Common-mode input resistance (RINCM) This parameter represents the ratio of the input common-mode voltage range to the change in bias current within this range when the operational amplifier operates in the linear region.

2. DC common mode rejection (CMRDC) This parameter is used to measure the ability of an operational amplifier to reject the same DC signal acting on both input terminals. CMRDC can be calculated using the common mode voltage range (CMVR) and the peak-to-peak value of the input offset voltage change corresponding to this range:

3. Common-mode AC rejection (CMRAC) CMRAC is a measure of the ability of an operational amplifier to reject the same AC signal applied to both inputs. It is a function of the differential open-loop gain divided by the common-mode open-loop gain. CMRAC is usually defined at a specific frequency and over the entire DC common-mode voltage range:

4. Gain Bandwidth Product (GBW) The gain bandwidth product AOL * ƒ is a constant that defines the region in the open-loop gain vs. frequency characteristic curve where it rolls off at -20dB/decade.

5. Input bias current (IB) This parameter refers to the average current flowing into the input terminal when the operational amplifier operates in the linear region.

6. Input bias current temperature drift (TCIB) This parameter represents the change in input bias current when the temperature changes. TCIB is usually expressed in pA/°C.

7. Input offset current (IOS) This parameter refers to the difference in current flowing into the two input terminals.

8. Input offset current temperature drift (TCIOS) This parameter represents the change in input offset current when the temperature changes. TCIOS is usually expressed in pA/°C.

9. Differential Input Resistance (RIN) This parameter represents the ratio of the change in input voltage to the corresponding change in input current. A change in voltage results in a change in current. When measured at one input, the other input is connected to a fixed common-mode voltage.

10. Output impedance (ZO) This parameter refers to the internal equivalent small signal impedance at the output end when the operational amplifier operates in the linear region.

11. Output Voltage Swing (VO) This parameter refers to the peak-to-peak value of the maximum voltage swing that can be achieved when the output signal is not clamped. VO is generally defined under a specific load resistance and power supply voltage.

12. Power consumption (Pd) refers to the static power consumed by a device at a given supply voltage. Pd is usually defined under no-load conditions.

13. Power Supply Rejection Ratio (PSRR) This parameter is used to measure the ability of an operational amplifier to keep its output unchanged when the power supply voltage changes. PSRR is usually expressed as the change in input offset voltage caused by a change in power supply voltage:

14. Slew rate (SR) This parameter refers to the maximum value of the ratio of the change in output voltage to the time required for this change. SR is usually expressed in V/μs, and sometimes also expressed as positive change and negative change respectively.

15. Supply Current (ICC, IDD) This parameter is the static current consumed by the device at a specified supply voltage. These parameters are usually defined under no-load conditions.

16. Unity-gain bandwidth (BW) This parameter refers to the maximum operating frequency of the operational amplifier when the open-loop gain is greater than 1.

17. Input offset voltage (VOS) This parameter indicates the voltage difference required to be applied to the input terminal to make the output voltage zero.

18. Input offset voltage temperature drift (TCVOS) This parameter refers to the change in input offset voltage caused by temperature changes and is usually expressed in μV/°C.

19. Input Capacitance (CIN) CIN represents the equivalent capacitance of any input terminal when the operational amplifier operates in the linear region (the other input terminal is grounded).

20. Input voltage range (VIN) This parameter refers to the range of input voltage allowed when the operational amplifier works normally (can obtain expected results). VIN is usually defined under the specified power supply voltage.

21. Input voltage noise density (eN) For operational amplifiers, input voltage noise can be regarded as a series noise voltage source connected to any input terminal. eN is usually expressed in nV / It is expressed in units of (nanovolts per root hertz) and is defined at a specified frequency.

22. Input Current Noise Density (iN) For an operational amplifier, input current noise can be considered as two noise current sources, connected to each input terminal and the common terminal, usually expressed in pA/ It is expressed in units and is defined at a specified frequency.