中图分类号： TN710.2
文献标识码： A
DOI：10.16157/j.issn.0258-7998.200240
中文引用格式： 张宏强，王勇，刘乃安. 晶体三极管开关混频电路研究[J].电子技术应用，2020，46(9)：127-131，136.
英文引用格式： Zhang Hongqiang，Wang Yong，Liu Naian. Research on BJT switch mixing circuit[J]. Application of Electronic Technique，2020，46(9)：127-131，136.

Research on BJT switch mixing circuit

Abstract： In allusion to the problem that traditional multiplier mixing method is affected by local oscillator and there exists interferences and distortions, which greatly affects the performance of receiver, a bipolar junction transistor(BJT) switch mixing method is proposed. The mathematical formula of switch mixing is deduced in detail, and two mathematical models, I-type and II-type switch mixing models are proposed by using Fourier series expansion of square wave. Based on NPN BJT switch, a mixing circuit is designed, and simulation is carried out on Multisim software environment. AM signal is used as an example to mix on BJT switch. Acceleration capacitor is added to eliminate negative peak cutting distortion and intermediate frequency signal is filtered out. The results of simulation are ideal. It is proved theoretically and practically that BJT switch mixing method prevents the interference of local oscillator signal, which can enhance receiver performance.

Key words : bipolar junction transistor；mixing；local oscillator signal；Fourier series；acceleration capacitor