Design of an Adaptive Lock-in Amplifier for the Terahertz System

In order to extract the weak terahertz signal in the terahertz time-domain spectroscopy (THz-TDS), and to solve the problem of single amplification of the existing lock-in amplifier or manual adjustment of the amplification, a lock-in amplifier with self-adaptive adjustment function for phase and amplification is designed. Compared with the traditional lock-in amplifier, it reduces the use of electronic components such as phase shifters, modulators and summators, and reduces the development cost of the circuit. The phase shifting module and the amplification factor of the amplifying circuit are controlled by the MCU control unit and the magnitude of the received feedback signal respectively. The dynamic range of the terahertz time-domain spectroscopy system using phase and amplification adaptive lock-in amplifiers indoors can reach 70dB. The test results show that the designed lock-in amplifier can effectively improve the dynamic range of the terahertz system, and is more convenient for real-life applications. (paper)