A direct current amplifier is described that has automatic zero adjust
ment and is suitable for signal sources with a voltage signal of less
than 1 muV. The amplifier has a gain of 100, a bias-voltage temperatur
e drift of 0.1 muV/degrees-C, a noise voltage (double the amplitude an
d reduced to the input) of less than 1 muV, and an input-voltage diffe
rence time drift after half an hour warming of under 0.5 muV/h.