Lock-in amplifiers are used to detect and measure very small AC signals down to the range of nVs. Accurate measurements may be made even when the small signals are buried by noise sources thousands of times larger. With the digital signal processing (DSP) technology involved in modern instrumentation, a lock-in amplifier is more versatile than sensing and recover small signals. Combining the virtual instrumentation technology, we reorganize the functional blocks of a programmable lock-in amplifier and build it as a virtual spectrum analyzer, virtual impedance meter, virtual network analyzer, virtual semiconductor parameter analyzer, signal generator, etc. A 4 layer model is used to implement these virtual instruments. The same virtual instrument can also be implemented on a general purpose FPGA developing board.