The AD549 is a monolithic electrometer operational amplifier with very low input bias current. Input offset voltage and input offset voltage drift are laser trimmed for precision performance. The AD549's ultralow input current is achieved with "Topgate" JFET technology, a process development exclusive to Analog Devices. This technology allows the fabrication of extremely low input current JFETs compatible with a standard junctionisolated bipolar process. The 1015 common-mode impedance, a result of the bootstrapped input stage, insures that the input current is essentially independent of common-mode voltage. The AD549 is suited for applications requiring very low input current and low input offset voltage. It excels as a preamp for a wide variety of current output transducers such as photodiodes, photomultiplier tubes, or oxygen sensors. The AD549 can also be used as a precision integrator or low droop sample and hold. The AD549 is pin compatible with standard FET and electrometer op amps, allowing designers to upgrade the performance of present systems at little additional cost. The AD549 is available in a TO-99 hermetic package. The case is connected to Pin 8 so that the metal case can be independently connected to a point at the same potential as the input terminals, minimizing stray leakage to the case. *Protected by Patent No. 4,639,683.