OPTIMAL CURRENT FOR MINIMUM THERMAL NOISE OPERATION OF SUBMICROMETER MOS-TRANSISTORS

The wide band noise voltage (equivalent thermal noise voltage at the g ate) of a submicron MOSFET, working in saturation, exhibits a minimum value at a certain drain current. This is supported by measurements an d theoretical analysis based on a suitable thermal noise model, This m acroscopic noise model attributes the thermal noise of the drain curre nt to the superposition of two noise sources originating from two sepa rate regions of the transistor's channel (a gradual channel approximat ion region and a saturation region). The existence of a minimum of the noise spectral density at an optimum drain current (I-opt), is well p roved by measurements and is contradictory to the predictions of the c urrent simulation program with integrated circuit emphasis (SPICE) mod els, An empirical way for evaluating analytically I-opt is given, The fact of the existence of a noise minimum for a submicron MOSFET, bring s a phenomenological equivalence to the bipolar transistor and GaAs ME SFET when they are employed at the first stage of an amplifier.