Single-photon detectors play a key role in many research fields such as biology, chemistry, medicine, and space technology, and in recent years, single-photon avalanche diodes (SPADs) have become a valid alternative to photo multiplier tubes (PMTs). Moreover, scientific research has recently focused on single-photon detector arrays, pushed by a growing demand for multichannel systems. In this scenario, we developed a compact 32-channel system for time-resolved single-photon counting applications. The system is divided into two independent modules: a photon detection head including a 32 Â 1 SPAD array built in custom technology, featuring high time resolution, high photon detection efficiency (44% at 550 nm), and low dark count rate (mean value G 400 cps at À10 C) at 6-V excess bias voltage and a 32-channel acquisition system able to perform timecorrelated single-photon counting (TCSPC) measurements. The TCSPC module includes eight four-channel time-to-amplitude converter (TAC) arrays, built-in 0.35-m Si-Ge BiCMOS technology, characterized by low differential non-linearity (rms value lower than 0.15% of the time bin width) and variable full-scale range. The system response function of this TCSPC instrumentation achieves a mean time resolution of 63 ps FWHM , considering a mean count rate of 1 Mcps.
Nowadays, an increasing number of applications require high-performance analytical instruments capable to detect the temporal trend of weak and fast light signals with picosecond time resolution. The Time-Correlated Single-Photon Counting (TCSPC) technique is currently one of the preferable solutions when such critical optical signals have to be analyzed and it is fully exploited in biomedical and chemical research fields, as well as in security and space applications. Recent progress in the field of single-photon detector arrays is pushing research towards the development of high performance multichannel TCSPC systems, opening the way to modern time-resolved multi-dimensional optical analysis. In this paper we describe a new 8-channel high-performance TCSPC acquisition system, designed to be compact and versatile, to be used in modern TCSPC measurement setups. We designed a novel integrated circuit including a multichannel Time-to-Amplitude Converter with variable full-scale range, a D∕A converter, and a parallel adder stage. The latter is used to adapt each converter output to the input dynamic range of a commercial 8-channel Analog-to-Digital Converter, while the integrated DAC implements the dithering technique with as small as possible area occupation. The use of this monolithic circuit made the design of a scalable system of very small dimensions (95 × 40 mm) and low power consumption (6 W) possible. Data acquired from the TCSPC measurement are digitally processed and stored inside an FPGA (Field-Programmable Gate Array), while a USB transceiver allows real-time transmission of up to eight TCSPC histograms to a remote PC. Eventually, the experimental results demonstrate that the acquisition system performs TCSPC measurements with high conversion rate (up to 5 MHz/channel), extremely low differential nonlinearity (<0.04 peak-to-peak of the time bin width), high time resolution (down to 20 ps Full-Width Half-Maximum), and very low crosstalk between channels.
Modern time-correlated single-photon counting (TCSPC) systems can achieve very high performance, but advanced applications also demand the implementation of multichannel acquisition chains. To fit the specifics of TCSPC applications we developed a complete single-channel measurement system, composed by three main parts: a single-photon detection module, a TCSPC acquisition board and a power management unit. The system is based on a single-photon avalanche diode (SPAD) and on a fully integrated time-to-amplitude converter (TAC). We designed the module to be very compact, in order to be enclosed in a small case (110 × 50 × 40 mm). The system features high temporal resolution (71 ps), low differential nonlinearity (0.05 LSB), high counting rate (4 MHz) and low power. Moreover a four-channel TAC has already been manufactured and tested; the very low crosstalk between channels, together with low power and low area make the converter suitable for large scale multi-channel acquisition chains, allowing the implementation of architectures for multidimensional TCSPC measurements
Modern Time-Correlated Single-Photon Counting applications require to detect spectral and temporal fluorescence data simultaneously and from different areas of the analyzed sample. These rising quests have led the development of multichannel systems able to perform high count rate and high performance analysis. In this work we describe a new 32-channel TCSPC system designed to be used in modern setups. The presented module consists of four independent 8-channel TCSPC boards, each of them including two 4-channel Time-Amplitude Converter arrays. These TAC arrays are built-in 0.35 μm Si-Ge BiCMOS technology and are characterized by low crosstalk, high resolution, high conversion rate and variable full-scale range. The 8-channel TCSPC board implements an 8-channel ADC to sample the TAC outputs, an FPGA to record and organize the measurement results and a USB 2.0 interface to enable real-time data transmission to and from an external PC. Experimental results demonstrate that the acquisition system ensures high performance TCSPC measurements, in particular: high conversion rate (5 MHz), good time resolution (down to 30 psFWHM with the full scale range set to 11 ns) and low differential non-linearity (rms value lower than 0.15% of the time bin width). We design the module to be very compact and, thanks to the reduced dimensions of the 8-channel TCSPC board (95×40 mm), the whole system can be enclosed in a small aluminum case (160×125×30 mm)
This paper describes an eight-channel differential pulse generator based on a fast differential bipolar transistor output stage. It has been designed specifically to test new multichannel time-correlated single-photon counting (TCSPC) instruments, while maintaining a wide range of regulation possibilities in terms of frequency, amplitude, delay, and duty cycle. The input signal for each channel can be provided either by an on-board programmable frequency synthesizer or by an external reference shared by all channels. The chosen input is delivered to a delayer loop controlled by a field programmable gate array (FPGA), which provides the desired delay, minimizing the jitter contribution. The delayed signal is fed to an analog differential stage that provides the fast output, whose amplitude and offset are adjusted by a digital-to-analog converter, controlled by the FPGA. The experimental results on the instrument show an output slew rate of 1600 V/$mu text{s}$ over the complete full-scale range, which is between -2 and 6 V. The feedback delayer regulates the delay between 0 ns and 30 $mu text{s}$ whereas the high time is adjustable from a minimum of 10 ns to a maximum of 30 $mu text{s}$ . Finally, the frequency range is from 2 kHz to 50 MHz. All these adjustable parameters are managed by a microcontroller that works as an interface between the FPGAs and dedicated PC software. The implemented structure allows the system to achieve a time resolution down to 6 ps across all channels, making this instrument perfect for testing high time resolution TCSPC systems
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