A very high precision 500-nA CMOS floating-gate analog voltage reference

A floating gate with stored charge technique has been used to implement a precision voltage reference achieving a temperature coefficient (TC) <1 ppm/°C in CMOS technology. A Fowler-Nordheim tunnel device used as a switch and a poly-poly capacitor form the basis in this reference. Differential dual floating gate architecture helps in achieving extremely low temperature coefficients, and improving power supply rejection. The reference is factory programmed to any value without any trim circuits to within 200 μV of its specified value. The floating-gate analog voltage reference (FGAREF) shows a long-term drift of less than 10 ppm/√1000 h. This circuit is ideal for portable and handheld applications with a total current of only 500 nA. This is done by biasing the buffer amplifier in the subthreshold region of operation. It is fabricated using a 25-V 1.5-μm E²PROM CMOS technology.