Floating gate analog voltage level shift circuit and method for producing a voltage reference that operates on a low supply voltage

Abstract

A floating gate voltage level shift circuit is disclosed for generating a voltage reference which can operate on a low supply voltage Vcc by providing a circuit that enables the floating gate to be set accurately to a positive voltage during a SET operation and subsequently shifted down to a lower voltage for a READ operation. The floating gate voltage level shift circuit comprises a differential amplifier with two floating gates, a first floating gate and a second floating gate where the second floating gate is capacitively coupled to either a READ voltage or a Vshift voltage. The floating gate voltage level shift circuit operates in two primary modes, a SET operation and a READ operation. During the SET operation, the C1p capacitor of the second floating gate is connected to a Vshift voltage, rather than ground, while accurately setting the floating gate a positive voltage. The output of the differential amplifier typically swings a volt or more above and below the voltage of the second floating gate while settling to a desired voltage. During the READ operation, the C1p capacitor of the second floating gate is connected to ground, thereby causing the floating gate to shift down to a lower voltage which enables the voltage reference to work on low supply voltage.