A linear NMOS depletion resistor and its application in an integrated amplifier

A linear resistor has been realized by using NMOS depletion transistors operated in the triode region. While such a resistor is mainly intended for single-ended and first quadrant mode of conduction, where it achieves a nonlinearity of .03% full scale in the 0-10 V voltage range, it can also be used as a floating element and operated in the first as well as third quadrant mode of conduction (i.e. with V and I both either positive or negative) with some degradation in linearity and voltage range. A linear noninverting amplifier with an accurately controlled gain of 16 has been realized by using a high open-loop gain (90 dB) operational amplifier and dimensioning the simulated resistors to set the closed-loop gain.