Lock-in amplifiers measure the amplitude and phase of signals obscured by noise. A lock-in amp allows users to isolate oscillating AC signals, even if the signal is up to a million times smaller than present noise components, and then amplify the signal. Common uses include recovering signals lost in noise and capturing high-resolution measurements of clean signals. Lock-in amps are also ideal test systems for a variety of other applications—measuring noise itself, determining a signal’s phase shift, or even taking the place of a range of measurement devices. In scientific applications, for example, they serve as AC voltage/phase meters, AC signal recovery instruments, spectrum analyzers, vector voltmeters, network analyzers and more.
Technicians looking for a high-quality lock-in test system should consider the following factors.
- Frequency range
- Lock-in amps now operate over frequency ranges up to 5 MHz and care should be taken to select the right model for your application.
- Input noise
- Input noise should be as small as possible, as the end goal is to produce a high signal-to-noise ratio.
- Dynamic reserve
- Dynamic reserve is an essential specification because it characterizes how well the amplifier rejects unwanted signal components while offering accurate results. An amp with high dynamic reserve can achieve or exceed 120 dB.
Lock-in amplifiers can be divided into analog and digital systems.
- Analog lock-in amps demodulate a signal by means of analog frequency mixers and RC filters; this process, also known as phase-sensitive detection, allows users to single out the component of the signal at a specific frequency and phase. This input signal is then multiplied by the reference signal and the two are integrated over a specified time period, which can be anything from a millisecond to a few seconds.
- Digital lock-in amplifiers utilize digital signal processing (DSP) to demodulate signals, increasing the speed and efficiency of the measurement. DSP empowers testers to perform measurements up to 600 MHz and surpass their analog counterparts in frequency range, stability, noise and dynamic reserve. A digital lock-in amplifier will also provide multiple demodulators, allowing the user to test multiple frequencies at once.
ATEC offers affordable rental rates for the industry’s leading products, including the Stanford Research Systems (SRS) SR830 lock-in amplifier and the Signal Recovery 7280.