Specifications
| Specification | Why it matters |
|---|---|
| Supply-voltage range | Must suit available power rails. |
| Input common-mode range | Defines valid input voltage territory. |
| Output swing | Defines available output voltage under load. |
| Input offset voltage | Creates DC gain error. |
| Offset drift | Shows change with temperature. |
| Input bias current | Creates error through source resistance. |
| Voltage/current noise | Sets low-level signal limits. |
| Gain-bandwidth product | Limits small-signal closed-loop bandwidth. |
| Slew rate | Limits large-signal speed. |
| CMRR | Rejection of voltage common to both inputs. |
| PSRR | Rejection of supply changes. |
| Output current | Limits load drive. |
| Quiescent current | Important in battery equipment. |
| Unity-gain stability | Determines whether gain-one operation is intended. |
Gain-bandwidth
Bandwidth ≈ GBW / noise gain
A 1 MHz op-amp used at noise gain 10 may have small-signal bandwidth on the order of 100 kHz.
Full-power bandwidth
fmax ≈ SR/(2πVPEAK)
Noise
Offset is a relatively steady error; noise is random variation. Precision DC work may prioritize offset and drift, while audio and sensor work may prioritize noise density and bandwidth.
Tradeoffs
There is no universal best op-amp. Low power, low noise, high speed, low offset, high voltage, and strong output drive often pull the design in different directions.