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DE-102024133065-A1 - Signal processing circuit for a photon detector and related signal processing method

DE102024133065A1DE 102024133065 A1DE102024133065 A1DE 102024133065A1DE-102024133065-A1

Abstract

The invention relates to a method for processing a time sequence of current pulses triggered at a photon detector 1 by a respective photon striking a sensor surface of the photon detector 1 and determining a detection signal D in a signal processing circuit, comprising the steps: - Converting a time sequence of analog current pulses, each triggered by a single photon in the photon detector 1, into two inverse analog voltage pulse sequences in a preamplifier (preamp). - Removing a respective DC offset component from the two mutually inverse voltage pulse sequences; - to set a trigger threshold, shifting the voltage potential of one of the two mutually inverse voltage pulse sequences with removed DC offset component by a predetermined, in particular adjustable, threshold voltage; - Comparing the pre-processed analog voltage pulse trains of the preamplifier output with a first comparator 3 and outputting a digital signal depending on the result of the comparison. The invention further relates to a signal processing circuit for carrying out such a method.

Inventors

  • Jens Raacke

Assignees

  • duotec GmbH

Dates

Publication Date
20260513
Application Date
20241112

Claims (16)

  1. A method for processing a time sequence of current pulses triggered at a photon detector, in particular a single-photon diode (1), by a photon incident on a sensor area of the photon detector (1), and determining a detection signal (D) in a signal processing circuit, wherein the detection signal (D) comprises a specification or sequence of times of detection events, wherein a detection event corresponds to the detection of a single photon, characterized by the steps: - Converting a time sequence of analog current pulses or corresponding analog voltage pulses triggered at a single photon in the photon detector (1) in a preamplifier, in particular a transducer. Simpedance amplifier (TIA) with differential output into two inverse analog voltage pulse trains (T1, T2), - removal of a respective DC offset component from the two mutually inverse voltage pulse trains (T1, T2) of the differential output of the preamp; - to set a trigger threshold, shifting the voltage potential of one of the two mutually inverse voltage pulse trains with removed DC offset component by a predetermined, in particular adjustable, threshold voltage; - Comparing the pre-processed analog voltage pulse trains of the output of the preamplifier (2) with a first comparator (3) and outputting a digital signal depending on the result of the comparison, in particular such that the output of the comparator (3) is set to a first potential if the first pre-processed voltage pulse signal of the output of the preamp is greater than the second pre-processed voltage pulse signal of the output of the preamp and the output of the comparator (3) is set to a second potential if the first pre-processed voltage pulse signal of the output of the preamp is greater than the second pre-processed voltage pulse signal of the output of the preamp, and preferably - performing a digital signal conditioning (9) of the digital signal (X2) output by the comparator (3) to generate a digital signal (Y) conditioned for further processing in digital circuits.
  2. Procedure according to Claim 1 , characterized in that the respective DC offset component of both inverse voltage pulse sequences (T1, T2) is removed by means of a respective coupling capacitor.
  3. Procedure according to Claim 1 or 2 , characterized in that the respective DC offset component of both inverse voltage pulse sequences of the preamp output is removed by means of a respective high-pass filter (R2, C2; R3, C3) and at the same time both voltage pulse sequences are shortened in time.
  4. Procedure according to one of the Claims 1 , 2 or 3 , characterized in that the shifting of the voltage potential of one of the two voltage pulse sequences with removed DC offset component by an adjustable threshold voltage is carried out by means of DC biasing.
  5. Procedure according to one of the Claims 1 until 4 , characterized in that the adjustable threshold voltage is provided by a microcontroller-controlled digital/analog converter (4).
  6. Procedure according to one of the Claims 1 until 5 , characterized in that a positive potential shift is applied to the negative output signal of the preamplifier (2).
  7. Procedure according to one of the Claims 1 until 6 , characterized in that in a calibration step for setting a trigger threshold with the photon detector (1) darkened, the threshold voltage is successively increased from a low value, in particular a voltage value of 0 V, to reduce photon false detections until a predetermined number of false detections per predetermined time is undercut and the trigger threshold is determined as a function of the target threshold voltage thus determined, or the determined target threshold voltage is set as the trigger threshold.
  8. Procedure according to one of the Claims 1 until 6 , characterized in that in a calibration step for setting a trigger threshold, a (time) sequence of current pulses is triggered by allowing a predetermined (time) sequence of test photons to strike the sensor surface of the photon detector (1) and the trigger threshold is set such that the detection signal (D) generated by the signal processing circuit has a detection error rate that is below a predetermined detection error rate threshold.
  9. Procedure according to one of the Claims 1 until 8 , characterized in that the digital signal conditioning of the digital signal (X2) output by the comparator (3) to generate a digital signal conditioned for further processing in digital circuits is carried out by means of a monostable flip-flop comprising a further comparator (8), wherein the further comparator (8) is arranged on the output side of the first comparator (3) and outputs the detection signal (D) at a differential output.
  10. Procedure according to Claim 9 , characterized in that the digital output signal (X2) of the first comparator (3) is applied to the comparator (8) of the monostable multivibrator via a voltage divider (6) and a capacitive coupling.
  11. Procedure according to one of the Claims 1 until 10 , characterized in that at least the photon detector (1) and the preamplifier (2) are actively cooled.
  12. Method in which detection signals (D) from at least four identical circuit arrangements, each for carrying out one of the above-mentioned procedures according to one of the Claims 1 - 11 are trained to be time-synchronized for the coordination of an encryption key for the encryption of data during a data transmission with a geographically remote communication point.
  13. Signal processing circuit for processing a time sequence of current pulses triggered at each photon detector, in particular at a single-photon diode (1), e.g., at an avalanche single-photon diode, by a respective photon striking a sensor area of the photon detector (1), and determining a detection signal (D) which, as information, comprises a sequence of time points of detection events, wherein a detection event corresponds to the detection of a single photon, comprising at least: - a preamplifier (2) with an input connectable to a photon detector (1) and a differential output, which receives on its input a sequence of current pulses or associated voltage pulses triggered at each photon detector (1) by a respective photon striking a sensor area of the photon detector (1) and converts them into two inverse, analog voltage pulse sequences (T1, T2) at its differential output, - for each a coupling capacitor or a high-pass filter connected to the differential output of the preamplifier (2) to remove a respective DC offset component of the two mutually inverse voltage pulse trains; - a DC biasing circuit for shifting the voltage potential of one of the two inverse voltage pulse trains with a removed DC offset component, in particular a microcontroller-controlled digital-to-analog converter circuit, which is coupled to the output of one of the two inverse voltage pulse trains; - a first comparator (3) which receives the pre-processed analog voltage pulse sequences from the output of the preamplifier (2) and outputs a digital signal sequence (X2) at an output, wherein the comparator (3) is configured and designed to set its output to a first digital potential when the first pre-processed voltage pulse signal is greater than the second pre-processed voltage pulse signal, and the output of the comparator (3) is set to a second digital potential when the first pre-processed voltage pulse signal is less than or equal to the second pre-processed voltage pulse signal, and preferably - a digital signal conditioning device (9) connected downstream of the first comparator (3) for providing the detection signal (Y, D), wherein the digital signal conditioning device (9) is arranged and designed to extend the digital signal output by the first comparator (3) in time.
  14. Signal processing circuit according to Claim 13 , characterized in that the digital signal conditioning device (9) has a monostable flip-flop (9) comprising a further comparator (8), wherein the further comparator (8) is arranged on the output side of the first comparator (3) and outputs the detection signal (D) at a differential output.
  15. Signal processing circuit according to Claim 13 or 14 , characterized in that the digital output signal (X2) of the first comparator (3) is applied to the comparator (8) of the monostable multivibrator via a voltage divider (6) and a capacitive coupling, wherein a capacitor (C5) of the capacitive coupling is connected to the output of the first comparator (3) and a center tap of the particularly high-impedance voltage divider (6).
  16. Detector device comprising a photon detector (1) and a signal processing circuit according to the invention connected thereto according to one of the Claims 13 until 15 , wherein the photon detector (1) provides an input signal (S) for the signal processing circuit.

Description

The invention relates to a method for processing a sequence of current pulses triggered at a photon detector by a photon striking a sensor area of the photon detector, and for determining a detection signal in a signal processing circuit, wherein the detection signal comprises a specification or sequence of times of detection events, a detection event corresponding to the detection of a single photon. The invention further relates to a signal processing circuit for carrying out such a method. Detecting extremely low light intensities, particularly single photons, presents a significant challenge in many fields, such as analytical applications in the life sciences (e.g., fluorescence and luminescence measurements), single-molecule spectroscopy, confocal microscopy, industrial applications like particle size determination, metrology, astronomical applications like LIDAR (Light Detection and Ranging), and quantum applications like quantum optics and quantum cryptography. A key problem in such applications is processing the current signals emitted by a photon detector in such a way as to suppress thermally induced dark count rates and differentiate photons arriving sequentially at the detector. Furthermore, minimizing dead time in signal processing is crucial. This dead time is typically caused by the need for very high amplification to detect single photons and by the necessary signal processing in the downstream electronics. Therefore, the present invention is based on the objective of providing a method for signal processing of a time sequence of current pulses triggered at a photon detector, with which the above-mentioned requirements can be met cost-effectively. This problem is solved by the present invention by a method for processing a time sequence of current pulses triggered at a photon detector by a photon striking a sensor area of the photon detector, and for determining a detection signal in a signal processing circuit, wherein the detection signal comprises a specification or sequence of times of detection events and wherein a detection event corresponds to the detection of a single photon. The method according to the invention comprises the following steps: - Converting a time sequence of analog current pulses or corresponding analog voltage pulses, each triggered by a single photon in the photon detector, in a preamplifier, in particular a transimpedance amplifier (TIA) with differential output, into two inverse analog voltage pulse sequences; - Removing a respective DC offset component from the two mutually inverse voltage pulse trains of the differential output of the preamp; - to set a trigger threshold, shifting the voltage potential of one of the two mutually inverse voltage pulse sequences with removed DC offset component by a predetermined, in particular adjustable, threshold voltage; - Comparing the pre-processed analog voltage pulse trains of the preamplifier output with a first comparator and outputting a digital signal or digital signal sequence depending on the result of the comparison, and - preferably, performing conditioning, in particular extending the time of the digital signal output by the first comparator to generate a digital signal or digital signal sequence conditioned for further processing in digital circuits. With the signal processing method according to the invention, it is now possible to derive a voltage pulse or voltage pulse train from the detection of a temporal sequence of individual photons, despite a very weak current pulse in the range of a few tens of µA and an output pulse duration in the range of approximately 50 ns triggered by a single photon at a photon detector. This is achieved with increased slope and reduction of the decaying, falling edge of the signal by means of high-pass filtering, thus enabling differentiation of individual photon detections within the generated digital detection signal. Furthermore, by setting the lowest possible trigger threshold, just above the noise floor, false detection signals can be avoided with a high degree of probability. Advantageously, the photon detector, in particular a single-photon diode with a bias voltage VBias, in particular a reverse bias voltage VBias, can be used to determine of the operating point of the photon detector. Advantageously, so-called single-photon avalanche diodes (SPADs) can be used as the signal source, i.e., as the photon detector. These diodes exhibit a high gain of approximately 10⁸ , since a single electron-hole pair generated by a photon can produce a large number of charge carriers due to acceleration in the multiplication region. Thus, an electron-hole pair generated in the semiconductor material of the diode by a single photon can, due to the described gain, generate a charge carrier avalanche, enabling the detection of the single photon. To prevent the diode from remaining conductive for too long due to the large number of generated charge carriers, and therefore exhibiting a long