Rail-to-rail, linear hot-electron injection programming of floating-gate voltage bias generators at 13-bit resolution

Hot-electron injection is widely used for accurate programming of on-chip floating-gate voltage and current references. The conventional programming approach involves adapting the duration and magnitude of the injection pulses based on a predictive model which is estimated by using measured data. However, varying the pulse-widths or amplitudes introduces nonlinearity in the injection process which complicates the modeling, calibration and programming procedure. In this paper, we propose a linear hot-electron injection technique which significantly simplifies the programming procedure, and can achieve programming accuracy greater than 13-b which is limited by the thermal noise from the injection process. The procedure employs an active feedback circuit which ensures that all the nonlinear factors affecting the hot-electron injection process are held constant, thus achieving a stable and controllable injection rate. Measured results using an array of floating-gate voltage reference prototyped in a 0.5-μm standard CMOS process demonstrate that the injection rates can be controlled from 0.1 to 4.1 V for the programmable voltage range. Using 50-ms injection pulses, we show that the average injection rate can be adapted from 6.9 to 250 μV/cycle.