【摘要】 针对传统的乘法器混频方式受本振信号影响,且存在很多干扰和失真,很大程度影响接收机的性能,采用晶体三极管开关混频方法解决这一问题。详细推导了开关混频的数学公式,通过对方波信号进行傅里叶级数展开,提出了I型、II型开关混频的数学模型,并针对NPN三极管开关电路提出设计方案。在Multisim软件环境中实施了仿真验证,以AM信号为例进行三极管开关混频,引入加速电容消除了电路的负峰切削失真,并滤出中频信号,仿真结果较为理想。理论和实践表明,基于晶体三极管开关的混频方式避免了本振信号的干扰,可提高接收机性能。更多还原

【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 de-signed, 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.更多还原