Integrated lock-in amplifier



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Texas Tech University


The sensitivity of a lock-in amplifier makes it an exceptionally useful instrument for extracting signals from noise, even when the noise and signal frequencies are close together. Lock-in amplifiers are widely used in situations involving low signal-to-noise ratios. These situations frequently arise when making accurate measurements, such as displacement, temperature, stress-strain and many others.

Lock-in amplifiers are widely and usefully applied in all fields of scientific research to obtain of signals from noise. However, most lock-in amplifiers are build as an instrument or a board instead of single chip. The price of either an instrument or a circuit board is expensive. For a wide-band lock-in amplifier instrument, the price is around $4,000 or up. Furthermore, for the purposes of reducing the size of products and the extra noise caused by signal transmission, the development of integrated lock-in amplifiers becomes essential.

In this thesis, an analog lock-in amplifier is developed. This lock-in amplifier consists of an instrumentation amplifier, OP amplifier, active resistor, switch capacitor filter, phase shifter, and multiplier. The fundamental theory of the lock-in amplifier will be discussed in Chapter 2. Also in that chapter, the principles of the "phase sensitive detector, the modulator, and the demodulator will be introduced, as well as the lock-in amplifier. The circuit design of each part of the lock-in amplifier will be presented in detail in Chapter 3. All the results of this lock-in amplifier design will be shown in Chapter 4. Finally in Chapter 5, conclusions about this design are drawn, and some recommendations are given for further research.