Three-stage programmable amplifying circuit is applied in the signal demodulation circuit of a smart microwave switch, the gain of each amplifying circuit is controlled by MCP4351 which is a multiple SPI digital potentiometer. The measurement circuit measured and got an output voltage of a potentiometer for adjusting sensitivity. According to constraint conditions, the system distributed the total gain corresponding to the voltage with no signal distortion, and formed gain distribution table. In the process, the second and the third gain were distributed by the linear assignment method, and the first gain was calculated through constraint conditions. In the demodulation operation, the CPU MSP430F149 gained the adjusted values of the digital potentiometer gain by checking allocation table, and adjusted resistance of the potentiometer according to values so as to realize the automatic control of the gain. This method does not need lots of complex gain calculation process by microcontroller, and saves the operation time and program storage space.%在智能微波开关信号解调电路中采用了三级程控放大电路,各级放大电路的增益由多路SPI数字电位器MCP4351控制.测量电路对灵敏度调节电位器输出电压进行测量,在保证各级输出不失真的情况下,根据约束条件分配测量结果所对应的总增益,并形成增益分配表.其中,第二、三级增益按照线性法分配,第一级增益按照约束方程计算得出.解调时,系统控制核心MSP430F149查增益分配表得到数字电位器的调整值,并按照调整值调节电位器的阻值,实现增益的自动控制.该方法不需要单片机进行大量复杂的增益计算过程,节省运行时间和程序存储空间.
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