Superconducting Nanowire Single-Photon Detectors (SNSPDs) are characterized by high detection efficiency, high counting rates, low dark count rates, and minimal timing jitter, making them indispensable in fields such as quantum information science, free-space optical communication, and fundamental physics. Conventional SNSPD architectures, however, require the superconducting nanowires to be biased with a constant current and necessitate continuously operating readout circuits to capture the output signals. This leads to efficiency issues under prolonged low-load conditions and poses significant challenges for the development of multi-pixel SNSPD arrays. This thesis begins by examining conventional SNSPD designs, critically analyzing the shortcomings of previous active quenching methods, and proposing improvements to the digital sub-circuit. The introduction of a differential amplifier in place of the original single-ended main amplifier successfully addresses output offset issues, pushing the count rate beyond 50MHz. Moreover, this work introduces a novel persistent current SNSPD that leverages the memory characteristic of persistent currents in a superconducting loop, enabling photon detection without the continuous drive from interface circuits, and allowing for unified readout. A design methodology for SNSPD loops is proposed based on various simulation techniques and the physical and electrical characteristics of SNSPDs. This methodology was applied to design multiple samples tailored to different loop coupling scenarios. Additionally, the thesis outlines the biasing and readout logic for the persistent current SNSPD, ensuring independent photon detection without external circuit interference. In the demonstration system, the energy consumption per detection event was measured at 7pJ, with the average power consumption dependent on the frequency of rebias operations.