A Low-Cost, Portable Alternative for a Digital Lock-In Amplifier Using TMS320C5535 DSP

A Lock-In Amplifier (LIA) is used to remove noise from an input signal by the use of a reference signal. Generally the sampling rate of LIAs is much higher than the required frequency in typical applications. Moreover the hardware configuration of LIAs is much better than the requirement. The signals are processed using high-end signal processors which increase the cost of LIA. This paper aims to develop an inexpensive and portable alternative for the digital lock-in amplifier. This will enable application of LIAs in remote locations and in distributed systems which require multiple signal processors simultaneously. Similar implementation exists on microcontrollers and embedded processors. This paper utilizes a Texas Instruments (TI) TMS320 series Digital Signal Processor (DSP) which is a low-power signal processor. The lock-in amplifier is implemented on a TMS320C5535 eZDSP board. Unlike other LIAs the reference signal is generated in the DSP, hence obviating the requirement for an external reference input. The output is obtained through UART interface and observed on a computer. It is tested with a noisy sinusoidal signal given as input and the output signal is plotted and verified.