US Patent 7613756 Random number generation apparatus and method

An apparatus and a method are provided for generating a random number, wherein the randomness of the random number is derived from thermal noise present across a pair of resistors. Each of the pair of resistors is defined to receive a respective input voltage and add a respective noise component to the input voltage. The output from each resistor in the pair of resistors is amplified to generate a noisy analog voltage that includes a representation of the random noise components added by the pair of resistors. The randomly varying noisy analog voltage is used to control a voltage controlled oscillator (VCO). The VCO generates a random digital signal based on the randomly varying noisy analog voltage. The random digital signal generated by the VCO is used to set a number of bits for defining a random number.