Modulating a reference allows maximum-value search for phase detection

摘要

A lock-in amplifier is a useful tool for measuring a signal's amplitude and phase. A data-acquisition card can digitize the amplifier's output signal, and software can calculate amplitude and phase. A DSP or a general-purpose processor can also calculate amplitude and phase. The circuit in this Design Idea integrates two Analog Devices (www.analog.com) AD9954 DDS (direct digital synthesizers) and an AD630 balanced modulator/ demodulator into a low-cost lock-in amplifier (Figure 1).