OPA637AP - 80MHz Precision Difet Op Amp DIP-8 | Texas Instruments

The Texas Instruments OPA637AP is a precision high-speed Difet (dielectrically isolated FET) operational amplifier delivering 80 MHz unity-gain bandwidth and 135 V/us slew rate, supplied in an 8-pin PDIP package and operating from dual supplies of +/-4.5V to +/-18V.

A high-speed operational amplifier is a voltage-feedback amplifier designed to combine wide bandwidth with DC precision, sitting within the hierarchy: op-amp -> precision amplifier -> analog signal conditioning IC -> semiconductor. Where general-purpose amplifiers trade speed for accuracy, precision high-speed parts like the OPA637 preserve both, enabling high-dynamic-range analog signal chains.

Key features of the OPA637AP include a very low maximum offset voltage of 100 uV, a maximum offset drift of 0.8 uV/C, and a maximum input bias current of only 5 pA thanks to the Difet (dielectrically isolated FET) input process. The amplifier settles fast to 0.01% accuracy and is unity-gain bandwidth specified at 80 MHz. Unlike its sibling OPA627, which is unity-gain stable, the OPA637 is stable only at closed-loop gains of 5 or greater - the compensation scheme de-compensates the amplifier to achieve its higher bandwidth, which is why the 80 MHz figure exceeds the OPA627's.

The Difet process uses dielectric isolation rather than junction isolation, sharply reducing input capacitance and leakage. This yields the picoampere-class bias current and low noise typically associated with JFET-input precision amplifiers while preserving the high slew rate needed for fast pulse and wideband AC signals.

Typical applications include wideband data-acquisition front ends, fast pulse amplification in test and measurement instruments, photodiode transimpedance stages with high closed-loop gain, and active filters in precision instrumentation.

A key design consideration: because the OPA637 requires a minimum closed-loop gain of 5 for stability, do not substitute it for the unity-gain-stable OPA627 in follower configurations. Verify noise-gain margins and use good high-frequency PCB layout with short feedback paths.

This page synthesizes distributor pricing, drop-in alternatives, pinout data, and practical design notes not found in the manufacturer datasheet.