A 126 μ W Readout Circuit in 65 nm CMOS with Successive Approximation-Based Thresholding for Domain Wall Magnet-Based Random Number Generator

We present a novel readout circuit for a ferromagnetic Hall cross-bar based random number generator. The random orientation of magnetic domains are result of anomalous Hall-effect. These ferromagnetic Hall cross-bar structures can be integrated with the read out circuit to form a plug and play random number generator. The system can resolve up to 15–20 µ V Hall-voltages from Hall probe. Application of current densities around 10¹²A/m² through the Ferromagnetic Hall cross-bar produces random Hall-voltage on the output terminals. To amplify the weak Hall-voltages (10–100 µ V) in the presence of DC offsets, a modulation scheme is used to up-convert the signal and a band-pass amplifier is used to amplify the modulated signal. The bandpass amplifier circuit, motivated by neural recording amplifier is designed in 65nm CMOS and consumes 126 µ W of power from a 1.2 V supply. Further, we present a successive approximation algorithm and its embedded implementation to set the desired threshold for digitizing the amplified Hall-voltage in presence of signal drift. Experimental results show that the resulting system can tolerate drifts in voltage up to 440 µ V.