逻辑门混频器的特性分析与选择

Choosing Suitable Logic Gate Mixer for Measuring Frequency Difference

在基于频率输出的传感器测量电路设计中,存在如何测量由测量参数引起的小频率增量问题,将被测信号和参考信号进行混频并进行滤波可以解决这个问题。将仅频率变化的两准数字信号施加于逻辑门进行混频,对混频器输出的特性进行了理论分析和实验验证,结果表明:异或门和同或门用作差频测量的混频器时,其输出效果明显好于其他基本逻辑门;当信号为占空比50%的方波时,异或门和同或门的输出中不含输入信号的频率,滤波电路相对简单。

In the design of measuring circuits based on frequency transducers,it is necessary to measure small frequency increments caused by the change of the measured parameter.The mixer receives inputs from the reference oscillator and the monitor oscillator,and a low pass filter produces an output with the difference of the two input frequencies.Two quasi-digital signals are connected to the inputs of the logic gate mixers and the output characteristics of the mixers are studied in theories and experiments.Results show that XOR and XNOR logic gate mixers have better performances for measuring difference frequency than other logic gate mixers.The duty cycle of input signals has an influence on the output performance of mixers and there is a simple low-pass filter circuit at 50% duty cycle.