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A SPAD-based random number generator pixel based on the arrival time of photons

Xu H, Massari N, Gasparini L, Meneghetti A, Tomasi A

Published Jan 1, 2019• 0 citations
OpenAlex

Abstract

A quantum random generator based on photon detection is here presented. The system consists of a photon source, typically a commercial LED, coupled with a detector with single photon detection capability. The detector is composed of a Single-Photon Avalanche Diode (SPAD) and a time stamp circuit, which samples the arrival time of impinging photons within a predefined temporal window. The proposed implementation optimizes the area, allowing embedding all circuitry into a single pixel, and increases the efficiency of random bit extraction. Moreover, the adopted fast pre-charge mode of the SPAD quenching circuit reduces the afterpulsing probability, and hence possible undesirable correlation in the resulting random bit sequence. Thanks to the implemented random bit extraction, experimental results show that the pixel has a flat behavior for a significant range of light intensity, which makes the pixel robust against variations of external PVT parameters. The maximum achievable bit rate has been measured equal to 1 Mbps, while random sequences are shown to pass NIST tests without any post-processing.

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A quantum random generator based on photon detection is here presented. The system consists of a photon source, typically a commercial LED, coupled with a detector with single photon detection capability. The detector is composed of a Single-Photon Avalanche Diode (SPAD) and a time stamp circuit, which samples the arrival time of impinging photons within a predefined temporal window. The proposed implementation optimizes the area, allowing embedding all circuitry into a single pixel, and increases the efficiency of random bit extraction. Moreover, the adopted fast pre-charge mode of the SPAD quenching circuit reduces the afterpulsing probability, and hence possible undesirable correlation in the resulting random bit sequence. Thanks to the implemented random bit extraction, experimental results show that the pixel has a flat behavior for a significant range of light intensity, which makes the pixel robust against variations of external PVT parameters. The maximum achievable bit rate has been measured equal to 1 Mbps, while random sequences are shown to pass NIST tests without any post-processing.
A quantum random generator based on photon detection is here presented. The system consists of a source of photons, typically a commercial LED, coupled with a detector with single photon detection capability. The detector in this case is represented by a single pixel consisting of a SPAD and a time stamp circuit, which samples the arrival time of impinging photons within a predefined temporal window. The proposed implementation increases the efficiency of random bit extraction and reduces the afterpulsing probability, which can introduce undesirable correlation to the measurement. Preliminary results are reported, showing that the pixel has a flat behavior for a relevant range of intensity of the light, which makes the pixel robust against variations of external PVT parameters
Experimental demonstration of a quantum random number generator based on one single-photon avalanche diode (SPAD) detector, a T / ( T − t ) pulse-shaped laser, and an field-programmable gate array (FPGA) acquisition module is presented. An integrated laser driver drives an external laser diode at 670 nm wavelength, whereas the SPAD with a photon detection probability of 18.5% is integrated together with an active quenching-resetting circuit. The SPAD detector generates counts for the interarrival time (IAT) measurement system implemented in an FPGA, where the change of the IATs between consecutive pulses is used to derive a random bit stream. It is shown how the application of a pulse-shaped laser driver can increase the performance of the system as compared to the continuous-wave operation of the laser diode to achieve the maximum generation rate of 5 Mbps while using a single SPAD. The generated numbers pass all randomness tests of the National Institute of Standards and Technology (NIST), Dieharder, and ENT test (pseudorandom number sequence test) suits.
A robust true random number generator (TRNG), able to assure high quality output at different working conditions, is an attractive solution in secure communication application, because it increases resilience against possible external attacks. Among different TRNGs, quantum RNGs (QRNG) represent a good candidate for such systems, because of their compactness, low cost and performance [1–6]. They typically consist of a source of photons, such as an attenuated LED, coupled to a detector with single photon capability (SPAD). Many works in the literature have used a single detector [1–4] for random bit extraction. These devices are characterized by a limited bit rate [1], which can be increased by exploiting the arrival time of photons at the cost of circuit and system complexity [2–4]. Recent works [5–6] proposed to implement an array of detectors based on SPAD working in parallel thus extending the speed of QRNG up to 5 Gb/s [5]. Despite the high bit rate, the main drawback of [5] is the strong dependence of each pixel bias on the impinging light intensity which forces the system to work only for a narrow range of photon flux that poses several constraints on the design of the final QRNG system, e.g. the need of a feedback control loop to maintain a constant flux of photons, and of a uniform distribution of light over the entire sensor. Moreover, it is impractical to implement algorithms for bit extraction to all detectors of the array because of different responses and mismatches among SPADs.
A compact quantum random number generator based on the measurement of the arrival time of photons is presented in this paper. The new system consists of a silicon nanocrystals light emitting device coupled with a SPAD-based detector, integrated in a 3D chip packaging. The miniaturization of the device allows a remarkable reduction of the system size with respect the state of the art. The detector consists of an array of 16 pixels connected to a cluster of 4 reconfigurable TDCs with 12 bit resolution each for photon time stamping. Maximum system bit rate, limited by the emission efficiency of the source, is 0.4 Mbps.
A compact quantum random number generator based on an array of Single Photon Avalanche Diode (SP AD) is presented here. As the main feature, the proposed chip has the capability to generate random numbers without the use of an external source of light. In the present approach, SP AD devices are used as emitters and as detectors. An embedded logic allows distinguishing dark events from events coming from the photon emission. The extracted random bit sequence shows a quite uniform distribution and after being post-processed by means of an integrated circuit, used to maximize the entropy of the system, is able to pass the AIS31 test. The average bit rate is 400 kbps.
A 16×1616\times 1616×16 Pixel Post-Processing Free Quantum Random Number Generator Based on SPADs
In this brief, we present a 16 × 16-pixel quantum random number generator (QRNG) based on Single-Photon Avalanche Diodes, implemented in CMOS 150-nm technology. Each pixel consists of two detectors, featuring 17.2 μm ×7.7 μm size, and an arbiter, based on a phase comparator, enhancing the working range of the generator. The QRNG has achieved a random bit efficiency of 90% at a given observation window of 200 ns. The maximum speed is up to 18.2 Mbps for the whole array due to limited readout capability. The measurement result shows the random numbers can pass the standard randomness test without any post-processing.