用于太赫兹时域光谱系统的锁定放大电路

Lock-in amplifier for THz-TDS system

针对目前商用锁定放大器在太赫兹光谱测量中存在的功能冗余、体积庞大、价格昂贵等问题,设计了一种精简的锁定放大电路。该电路采用基于ARM Cortex-M3内核的STM32微控制器产生相对相位可编程控制的斩波信号和参考信号,结合平衡调制/解调器AD630实现锁定放大功能。基于诺顿等效定理提出了一种电流输入型锁定放大器测试系统,实现电流输入型锁定放大器的性能评估。经测试,设计的锁定放大电路最大相对误差仅0.56%,动态范围达到84.2 dB。测试结果表明,该锁定放大电路满足太赫兹时域光谱系统中的应用需求。该锁定放大电路尺寸仅85×85 mm^(2),可通过串口指令编程控制参考信号相位、锁定放大增益和积分时间,并完成数据采集,便于系统集成应用。

In present terahertz spectrum measurement,the commercial lock-in amplifier for signal detection has disadvantages such as function redundancy,bulky size and high price.A simplified lock-in amplifier circuit was designed in view of these disadvantages.The circuit uses a STM32 controller based on ARM Cortex-M3 generating chopper signal and reference signal with programmable relative phase,driving a balanced modulator/demodulator to realize lock-in amplification.A test system for current mode lock-in amplifiers was proposed based on the Norton’s theorem to evaluate the performance of the designed lock-in amplifier.Test results show that the maximum relative error of designed lock-in amplifier is only 0.56%,and the dynamic range reaches up to 84.2 dB,which means that the designed circuit meets the requirement in THz-TDS system.The size of the designed lock-in amplifier circuit is only 85×85 mm^(2).Through a RS232 port,the reference signal phase,system gain and time constant can be programmed and the data acquisition can also be completed,which is convenient for integration and application for THz-TDS system.