Ultrahigh-speed bandpass delta-sigma modulators using resonant-tunneling devices

利用共振隧穿二极管（RTD）和高电子迁移率晶体管（HEMT），设计了多GHz连续时间多比特Δ-Σ调制器。首先设计了基本的电路模块，如量化器和Gm-C滤波器。本2位量化器由四个传统的单端的，以获得准差分工作模式。滤波器采用全差分HEMT运算放大器。低通和带通delta-sigma调制器，然后通过组合这些电路模块构建。采用InP基RTD/HEMT工艺进行了晶体管级电路仿真。设计了一个低通调制器，其分辨率为9位，输入带宽为100 MHz，时钟频率fc为13 GHz。对于带通调制器，在带宽为30 MHz，频率为4GHz时，获得了7位的分辨率.由于设计方法已被阐明，包括RTD器件模型用于电路模拟，进一步提高性能是可能的，在未来通过优化电路参数。我们的研究清楚地表明了RTD/HEMT为基础的多GHz的delta-sigma调制器的高潜力。

By using resonant-tunneling diodes (RTDs) and high-electron-mobility transistors (HEMTs), multi-GHz continuous-time multi-bit delta-sigma modulators have been designed. Fundamental circuit blocks, such as quantizers and Gm-C filters, were designed first. The present 2-bit quantizer consisted of four conventional single-ended ones to obtain a quasi-differential operation mode. The filters employed fully differential HEMT operational amplifiers. The lowpass and bandpass delta-sigma modulators were then constructed by combining these circuit blocks. Transistor-level circuit simulation was carried out by assuming InP-based RTD/HEMT technology. A lowpass modulator was successfully designed with a 9-bit resolution and a100-MHz input bandwidth BW at a clock frequency f_c of 13 GHz. Regarding a bandpass modulator, a 7-bit resolution was obtained for BW=30 MHz and f_c=4 GHz. Since the design method have been clarified including an RTD device model used in the circuit simulation, further improvement in performance is possible by optimizing circuit parameters in the future. Our study clearly demonstrated a high potential of RTD/HEMT-based multi-GHz delta-sigma modulators.