In this study, a novel type of Fourier transform radio spectrometer (termed as all-digital radio spectrometer; ADRS) has been developed in which all functionalities comprising a radio spectrometer including a sampler and Fourier computing unit were implemented as a soft-core on a field-programmable gate array (FPGA). A delay-line-based ramp-compare analog-to-digital converter (ADC), which was completely digital, was used, and two primary elements of the ADC, an analog-to-time converter (ATC) and a time-to-digital converter (TDC), were implemented on the FPGA. The sampling rate of the ADRS f and the quantization bit rate n are limited by the relation τ = 1/(2nf), where τ is the latency of the delay element of the delay-line. Given that the typical latency of the delay element implemented on FPGAs is ∼10 ps, the adoption of a low-quantization bit rate, which satisfies the requirements for radio astronomy, facilitates the realization of a high sampling rate up to ∼100 GSa s−1. In addition, as the proposed ADRS does not require a discrete ADC and can be implemented on mass-produced evaluation boards, its fabrication cost is much lower than that of conventional spectrometers. The ADRS prototype was fabricated with values of f = 600 MSa s−1 and n = 6.6 using a PYNQ-Z1 evaluation board, with a τ of 16.7 ps. The performance of the prototype, including its linearity and stability, was measured, and a test observation was conducted using the Osaka Prefecture University 1.85−m mm–submm telescope; this confirmed the potential application of the prototype in authentic radio observations. With a cost performance 10 times better (∼800 USD GHz−1) than conventional radio spectrometers, the prototype facilitates cost-effective coverage of intermediate frequency bandwidths of ∼100 GHz in modern receiver systems.

中文翻译：

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低成本快速傅里叶变换光谱仪的观察演示，该光谱仪具有在 FPGA 上实现的基于延迟线的斜坡比较 ADC

在这项研究中，开发了一种新型的傅里叶变换射电光谱仪（称为全数字射电光谱仪；ADRS），其中包括一个射电光谱仪（包括采样器和傅里叶计算单元）的所有功能都作为软核实现现场可编程门阵列（FPGA）。使用了一个基于延迟线的斜坡比较模数转换器 (ADC)，它是完全数字的，ADC 的两个主要元件，一个模数转换器 (ATC) 和一个时间到-数字转换器 (TDC)，在 FPGA 上实现。ADRS f 的采样率和量化比特率 n 受关系 τ = 1/(2nf) 的限制，其中 τ 是延迟线的延迟元件的延迟。鉴于在 FPGA 上实现的延迟元件的典型延迟约为 10 ps，采用满足射电天文要求的低量化比特率有助于实现高达~100 GSa s-1的高采样率。此外，由于所提出的 ADRS 不需要分立 ADC，并且可以在量产的评估板上实现，因此其制造成本远低于传统光谱仪。ADRS 原型使用​​ PYNQ-Z1 评估板制造，f = 600 MSa s-1 和 n = 6.6，τ 为 16.7 ps。测量了原型的性能，包括其线性度和稳定性，并使用大阪府立大学 1.85-m mm-submm 望远镜进行了测试观察；这证实了原型在真实无线电观测中的潜在应用。