SQUID Pulse Shaping Circuit for High-Rate SNSPD Readout
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Solution Overview
Problem
Conventional signal processing circuits for superconducting nanostrip single-photon detectors (SNSPDs) face challenges in reading out multiple signals simultaneously due to overlapping waveforms, leading to lost temporal information and reduced readout rates, especially when operating in low-temperature environments.
Innovation Solution
A signal processing circuit with a delay circuit and magnetic field cancellation mechanism is employed, where a pulse signal is delayed and magnetic fields are oriented oppositely to shape the voltage signal, allowing for reduced dead time and preservation of temporal information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple SNSPD signals are read out simultaneously using conventional circuits, then the readout rate increases, but the waveforms overlap causing loss of temporal information
Solution Approach 1:
The patent segments the pulse signal processing into two distinct temporal components: the rising edge (containing temporal information) and the falling edge (to be canceled). By using separate magnetic field receivers (first and second receivers) that selectively process these different segments of the pulse waveform, the circuit preserves the temporal information from the rise time while eliminating the overlapping dead time from the fall time through magnetic field cancellation.
2Loss of time
If the fall time of the pulse signal is reduced to increase readout rate, then the dead time decreases, but the temporal information in the rising edge may be compromised
Solution Approach 1:
The patent applies local quality by treating the rising edge and falling edge of the pulse signal differently. The first magnetic field receiver is optimized to capture the rising edge with high fidelity for temporal information, while the second receiver processes the falling edge for cancellation purposes. This localized differential processing allows the circuit to maintain high temporal resolution in the critical rise time region while minimizing dead time through aggressive fall time cancellation.
3Measurement precision
If a delay circuit is added to shape the voltage signal waveform, then the pulse width is controlled and temporal information is preserved, but the device complexity increases
Solution Approach 1:
The patent merges the delay circuit functionality directly into the transmission line structure itself, rather than adding it as a separate discrete component. The transmission line is designed with inherent delay characteristics that provide the necessary pulse shaping. Additionally, the magnetic field cancellation mechanism combines multiple functions (signal reception, delay, and waveform shaping) into an integrated approach, reducing overall circuit complexity while achieving precise pulse width control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed circuit effectively processes voltage signals with reduced dead time and maintains temporal information, enabling higher readout rates and scalability without increased power consumption.
Implementation Method 1
a SQUID including first and second magnetic field receivers that are magnetically coupled to the first transmission line in response to transmission of the pulse signal through the first transmission line
Implementation Method 2
a first delay circuit disposed in the first transmission line to delay the pulse signal, the first delay circuit being located between a part of the first transmission line that is magnetically coupled to the first magnetic field receiver and a part of the first transmission line that is magnetically coupled to the second magnetic field receiver
Implementation Method 3
a magnetic field input to the first magnetic field receiver and a magnetic field input to the second magnetic field receiver are oriented in opposite directions such that a voltage signal transmitted through the second transmission line has a pulse width equal to the delay time
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
A signal processing circuit includes: a first transmission line through which a pulse signal is transmitted; a SQUID including first and second magnetic field receivers that are magnetically coupled to the first transmission line in response to transmission of the pulse signal through the first transmission line; a second transmission line connected to a current source and the SQUID; and a delay circuit disposed in the first transmission line to delay the pulse signal, the delay circuit being located between a part of the first transmission line that is magnetically coupled to the first magnetic field receiver and a part of the first transmission line that is magnetically coupled to the second magnetic field receiver. The delay time set for the pulse signal by the delay circuit is shorter than the sum of the rise time and the fall time of the pulse signal. A magnetic field input to the first magnetic field receiver and a magnetic field input to the second magnetic field receiver are oriented in opposite directions such that a voltage signal transmitted through the second transmission line has a pulse width equal to the delay time.