可调增益均衡性宽带MMIC低噪声放大器设计

文章提出了一种新颖的具有可调增益均衡特性的宽带全单片低噪声放大器电路设计方法,它将用于微波功率模块(MPM)的固态功率放大器(SSPA)链前端中的两项功能独立的电路(多级单片宽带低噪声放大器LNA和单片宽带频率均衡放大器FEA)组合设计在一块单片电路芯片中。其中LNA部分采用高效率高增益宽带级联型分布放大器取代常规的行波式分布放大器,使得放大器级数显著减少;频率均衡放大器提出用一种利用FET作可调元件的嵌入式低损无源网络来取代,使得放大器的增益特性在频带中部下凹可调,补偿了行波管“山丘状”功率增益特性。在此基础上完成设计的 MMIC LNA,仅使用3个0．25μm×120μm pHEMT,在6GHz～18GHz频带内,小信号增益14．3 ±0．8 dB,输入、输出反射损耗<-10 dB,NF<5 dB;嵌入可调增益均衡网络后,在其他性能参数基本保持不变的前提下,频带中部引入的电调衰减范围超过6．5 dB,完全满足MPM要求。

Design of a Novel Monolithic Multi-Octave-Frequency-band Low Noise Amplifier with Adjustable Gain-equalizing Characteristic

The design approaches of a novel multi-octave-frequency-band low-noise amplifier with an adjustable gain equalizing characteristic have been developed in this paper. The amplifier combines two different circuits ( multi-stage monolithic wide-band low-noise amplifier and monolithic wide-band frequency-equalizing amplifier ), which consist of the front-end of the solid-state power amplifiers ( SSPA ) for microwave-power-module (MPM ) use, into a single MMIC chip. The cascaded single-stage distributed amplifier ( CSSDA ) with much better performances in gain and efficiency has replaced the conventional traveling-wave distributed amplifier in designing which results in greatly reducing amplifier stages of LNA. A low-loss passive network, in which a FET was adopted as an adjustable element, was embedded in the amplifier. This simple embedded network makes the circuit's gain-band characteristic curve 'concave' and adjustable which compensates for the "hill-like" gain response of Traveling-Wave Tube. Based on the analysis, the designed MMIC 2-stage low-noise amplifier uses only 3 0.25 μm×120 μm pHEMTs and has the performance: in the frequency-range of 6 GHz-18GHz, small-signal gain of 14.3±0.8 dB, input and output return loss<-10 dB, and NF<5 dB. When the adjustable gain-equalizing network was embedded, the amplifier gain at middle frequency-band can be attenuated more than 6.5 dB with other performance approximately invariable, which fully satisfied the demand of MPM.