Some bipolar op amps provide lower voltage noise performance, but both voltage noise and bias current noise contribute to the total noise of a system. The OPA6x7 provide both low voltage noise and low current noise. These features provide excellent noise performance over a wide range of sources, including a reactive-source impedance. The excellent noise performance can be seen in the performance curve showing the noise of a source resistor combined with the noise of an OPA627. Greater than a 2kΩ source resistance, the op amp contributes little additional noise. Less than 1kΩ, op-amp noise dominates over the resistor noise, but compares favorably with precision bipolar op amps.