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 µV Hall-voltages from Hall probe. Application of current densities around 10 12 A/m 2 through the Ferromagnetic Hall cross-bar produces random Hall-voltage on the output terminals. To amplify the weak Hall-voltages (10-100 µV) 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 band-pass amplifier circuit, motivated by neural recording amplifier is designed in 65nm CMOS and consumes 126 µW 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 µV.
I. INTRODUCTIONRandom bit streams find application in generating keys in cryptography and initialization of parameters in a encrypted communication protocols. Random number generators are useful in realising Physically Unclonable Function (PUF) in microprocessors [1], [2]. These streams are also useful in stochastic simulations, gaming and events where random sampling is required. Random number generators can be divided into two classes based on their source, namely true random number generator (TRNG) and pseudo random number generator (PRNG). TRNG generates randomness from inherent stochastic physical feature of the source. On the other hand PRNG generates lengthy stream of digital bits which are difficult to predict. Most on-chip TRNG of present day use techniques like sampling of thermal noise [3] or exploiting meta stability of latching circuits [4]. Recently, magnetic random number generators (MRNG) have been proposed which *Corresponding Author is Arindam Basu. Equal contribution of Govind and Joydeep.