Photon Detection Characteristics and Error Performance of SPAD Array Optical Receivers

In this paper a novel photon counting receiver for optical communication applications is proposed. The proposed receiver is a single photon avalanche diode (SPAD) array which can provide a significantly improved detection sensitivity compared to conventional photodiodes. First, the detection statistics and main characteristics of a single SPAD receiver is presented, and the effects of the SPAD dead time, which is introduced by the quenching process, on the counting probability and effective count rate are studied. The approach is then extended to account for SPAD arrays. Using a Gaussian approximation, the counting distribution of a large size SPAD array is derived and effective count rate of arrays with different sizes is evaluated and compared. It is found that even in SPAD arrays, dead time still has a significant role in the maximum achievable count rate, and the fill factor of the array greatly affects the performance and count rate and has to be carefully dealt with. The impact of SPAD background counts and fill factor on the error performance of an on-off keying (OOK) modulation optical communication system is also investigated. It is shown that the bit error rate (BER) depends critically on back ground counts and improves with increasing fill factor

Noise Analysis in VLC Optical Link based Discrette OP-AMP Trans-impedance Amplifier (TIA)

To design Visible Light Communication (VLC) system, there are several requirements that needs to be met. One of the requirements is an active component selection (e.g. Op Amp). As an ideal communication system, VLC system has to be able to provides wide bandwidth access with minimum noise. The Transimpedance amplifiers (TIAs) is one of main components in optical system which is placed in the first stage of receiver system. It is used to convert the current output from photodiode to voltage. We have designed a 1 MHz fGBW TIA with low noise (in μVrms range). This paper aims to explain the design and implementation of TIA circuit with photovoltaic topology which cover empirical calculations and simulation of TIA’s bandwidth and its noise sources, i.e. resistor feedback noise, current noise, voltage noise and total noise based on RSS. The OP-AMP is chosen from Texas Instruments product, OPA 380, and photodiode is chosen from OSRAM, SFH213, then simulated by TINA-TI SPICE® software. The noise in TIA circuit is analyzed clearly. The developed kit is ready to be implemented in VLC system

The Bit Error Performance and Information Transfer Rate of SPAD Array Optical Receivers

In this paper the photon counting characteristics, the information rate and the bit error performance of single-photon avalanche diode (SPAD) arrays are investigated. It is shown that for sufficiently large arrays, the photocount distribution is well approximated by a Gaussian distribution with dead-time-dependent mean and variance. Because of dead time, the SPAD array channel is subject to counting losses, part of which are due to inter-slot interference (ISI) distortions. Consequently, this channel has memory. The information rate of this channel is assessed. Two auxiliary discrete memoryless channels (DMCs) are proposed which provide upper and lower bounds on the SPAD array information rate. It is shown that in sufficiently large arrays, ISI is negligible and the bounds are tight. Under such conditions, the SPAD array channel is precisely modelled as a memoryless channel. A discrete-time Gaussian channel with input-dependent mean and variance is adopted and the properties of the capacity-achieving input distributions are studied. Using a numerical algorithm, the information rate and the capacity-achieving input distributions, subject to peak and average power constraints are obtained. Furthermore, the bit error performance of a SPAD-based system with on-off keying (OOK) is evaluated for various array sizes, dead times and background count levels