If you have experimented with op amp circuits at moderate gain and frequency, you probably have noted very good agreement between actual performance and ideal performance. As gain and/or frequency are increased, however, certain op amp limitations come into play that effect circuit performance.

In theory, with proper understanding of the internal structures and processes used to fabricate an op amp, we could calculate these effects. Thankfully this is not necessary, as manufacturers provide this information in data sheets. Proper interpretation of data sheet specifications is required when selecting an op amp for an application.

## Operational Amplifier Glossary

**Average temperature coefficient of input offset current**

The ratio of the change in input offset current to the change in free-air temperature. This is an average value for the specified temperature range. Usually measured in μV/°C.

**Average temperature coefficient of input offset voltage **

The ratio of the change in input offset voltage to the change in free-air temperature. This is an average value for the specified temperature range. Usually measured in μV/°C.

**Phase margin**

The absolute value of the open-loop phase shift between the output and the inverting input at the frequency at which the modulus of the open-loop amplification is unity.

**A****m**** Gain margin**

The reciprocal of the open-loop voltage amplification at the lowest frequency at which the open-loop phase shift is such that the output is in phase with the inverting input.

**A****V**** Large-signal voltage amplification**

The ratio of the peak-to-peak output voltage swing to the change in input voltage required to drive the output.

**A****VD ****Differential voltage amplification**

The ratio of the change in the output to the change in

**Input offset current**

The difference between the currents into the two input terminals with the output at the specified level.

**I****n**** Equivalent input noise current**

The current of an ideal current source (having internal impedance equal to infinity) in parallel with the input terminals of the device that represents the part of the internally generated noise that can properly be represented by a current source.

**I****OL****Low-level output current**

The current into an output with input conditions applied that according to the product specification will establish a low level at the output.

**Short-circuit output current**

The maximum output current available from the amplifier with the output shorted to ground, to either supply, or to a specified point.

**Supply voltage sensitivity**

The absolute value of the ratio of the change in input offset voltage to the change in supply voltages. Notes: 1. Unless otherwise noted, both supply voltages are varied symmetrically. 2. This is the reciprocal of supply rejection ratio.

**Supply voltage rejection ratio**

The absolute value of the ratio of the change in supply voltages to the change in input offset voltage. Notes: 1. Unless otherwise noted, both supply voltages are varied symmetrically. 2. This is the reciprocal of supply sensitivity.

**P****D ****Total power dissipation**

The total dc power supplied to the device less any power delivered from the device to a load. Note: At no load: PD = VCC+ • I

**Input resistance **

The resistance between the input terminals with either input grounded.

**Differential input resistance**

The small-signal resistance between two ungrounded input terminals.

**Output resistance**

The resistance between an output terminal and ground.

**Slew rate**

The average time rate of change of the closed-loop amplifier output voltage for a step-signal input.

**Rise time**

The time required for an output voltage step to change from 10% to 90% of its final value.

**Total response time**

The time between a step-function change of the input signal and the instant at which the magnitude of the output signal reaches, for the last time, a specified level range (±e)containing the final output signal level.

**Input voltage range**

The range of voltage that if exceeded at either input may cause the operational amplifier to cease functioning properly.

**Input offset voltage**

The dc voltage that must be applied between the input terminals to force the quiescent dc output voltage to zero or other level, if specified.

** ****Common-mode input voltage**

The average of the two input voltages.

** ****Common-mode input voltage range**

The range of common-mode input voltage that if exceeded may cause the operational amplifier to cease functioning properly.

** ****Equivalent input noise voltage**

The voltage of an ideal voltage source (having internal impedance equal to zero) in series with the input terminals of the device that represents the part of the internally generated noise that can properly be represented by a voltage source.

** V****01****/V****02**** Crosstalk Attenuation**

The ratio of the change in output voltage of a driven channel to the resulting change in output voltage of another channel.

** V****OH**** High-level output voltage**

The voltage at an output with input conditions applied that according to the product specifications will establish a high level at the output.

** V****OL**** Low-level output voltage**

The voltage at an output with input conditions applied that according to the product specifications will establish a low level at the output.

** V****ID**** Differential input voltage**

The voltage at the non-inverting input with respect to the inverting input.

** V****OM**** Maximum peak output voltage swing**

The maximum positive or negative voltage that can be obtained without waveform clipping when quiescent dc output voltage is zero.

** V****O(PP)**** Maximum peak-topeak output voltage swing**

The maximum peak-to-peak voltage that can be obtained without waveform clipping when quiescent dc output voltage is zero.

** Z****ic**** Common-mode input impedance**

The parallel sum of the small-signal impedance between each input terminal and ground.

** z****o**** Output impedance**

The small-signal impedance between the output terminal and ground.

** Overshoot factor **

The ratio of the largest deviation of the output signal value from its final steady-state value after a step-function change of the input signal to the absolute value of the difference between the steady-state output signal values before and after the step-function change of the input signal.

** THD + N**** ‡****Total harmonic distortion plus noise**

The ratio of the RMS noise voltage and RMS harmonic voltage of the fundamental signal to the total RMS voltage at the

output.

** GBW**** ‡ ****Gain bandwidth product**

The product of the open-loop voltage amplification and the frequency at which it is measured.

** ‡ ****Average long-term drift coefficient of input offset voltage**

The ratio of the change in input offset voltage to the change time. This is an average value for the specified time period. Usually measured in μV/month.