The OPA128 is an ultra-low bias current monolithic operational amplifier. Using advanced geometry dielectrically-isolated FET (Difet) inputs, this monolithic amplifier achieves a performance level exceeding even the best hybrid electrometer amplifiers. Laser-trimmed thin-film resistors give outstanding voltage offset and drift performance. A noise-free cascode and low-noise processing give the OPA128 excellent low-level signal handling capabilities. Flicker noise is very low. The OPA128 is an improved pin-for-pin replacement for the AD515.