A floating-gate comparator with automatic offset adaptation for 10-bit data conversion

We present a novel voltage comparator that uses nonvolatile floating-gate charge storage for either offset nulling or automatic programming of a desired offset. We exploit the negative feedback mechanism of pFET hot-electron injection to achieve fully automatic offset cancellation. The adaptation guarantees an input offset less than the input-referred noise level regardless of initial device offset for a typical 8.3% observed injection mismatch. In addition, we demonstrate the ability to accurately program a desired offset. The design has been fabricated in a commercially available 0.35-μm process. Experimental results confirm the ability to reduce the variance of the initial offset by two orders of magnitude and to accurately program a desired offset with maximum observed deviation 728 μV and typical deviation 109 μV. The mean offset is reduced by a factor of 416 relative to fabricated chips directly from the foundry and by a factor of 202 relative to UV-irradiated chips. Adaptation is fast, with settling time typically under 50 ms and scaling inversely with the exponential of the injection voltage. We achieve controlled injection to accurately program the input offset to voltages uniformly distributed from - 1 to 1 V. The comparator exhibits a 5 ns propagation delay and consumes 270 μW.