Study On Key Technique Of Digital Lock-in Amplifier

The Detection of the milli-volt signal is often required in scientific research and engineering practice. Many weak signals which can not be detected with the conventional method, such as micro-vibration, weak voltage, weak current and small change of temperature, can be detected through the lock-in amplifier. So the lock-in amplifier is one of important methods for weak signal detection, which has been widely applied in the field of physics, chemistry, biomedicine, remote sensing, material science, etc.In this thesis, the author studied the existing lock-in amplifier in depth and presented a novel design of lock-in amplifier. The main work of this paper is shown as follows:1. A novel digital the lock-in amplifier based on DSP (TMS320CV5416) is designed. The complicated programmable logic device (EPM7064) is used to manipulate the external logic and system time sequence, which improves the stability and real-time ability of the system.2. The high-speed acquisition circuit is designed according to the popular circuit structure, which connects the A/D chip with DSP together to get high acquisition rate through FIFO. Otherwise, a high-speed data acquisition circuit is designed with the parallel interface of computers and the HPI interface of DSP which forms a high-speed tunnel between the host computer and DSP, so that the system can deal with high-speed communication.3. The software for DSP and PC is designed to work with the hardware system, which accomplishes the control of hardware circuit, communication between DSP and PC and calculation of the acquired data.The signal from signal generator (ESCORT EGC-3230) is measured on the platform. According to the spectrum of the data and the result of orthogonal digital demodulation, relative error and repeatability error of the acquired data are obtained. The experimental tests compared with oscillograph show that the system meets the design demand.