The OPA121 is a precision monolithic dielectricallyisolated FET (Difet ) operational amplifier. Outstanding performance characteristics are now available for low-cost applications. Noise, bias current, voltage offset, drift, open-loop gain, common-mode rejection, and power supply rejection are superior to BIFET amplifiers. Very low bias current is obtained by dielectric isolation with on-chip guarding. Laser-trimming of thin-film resistors gives very low offset and drift. Extremely low noise is achieved with new circuit design techniques (patented). A new cascode design allows high precision input specifications and reduced susceptibility to flicker noise. Standard 741 pin configuration allows upgrading of existing designs to higher performance levels.