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About Lock-In Amplifiers
Application Note #3
Lock-in amplifiers are used to detect and measure very small
AC signalsall the way down to a few nanovolts. Accurate Reference
measurements may be made even when the small signal is
obscured by noise sources many thousands of times larger.
Lock-in amplifiers use a technique known as phase-sensitive sig
detection to single out the component of the signal at a
specific reference frequency and phase. Noise signals, at Signal
frequencies other than the reference frequency, are rejected
and do not affect the measurement.
Why Use a Lock-In?
Let's consider an example. Suppose the signal is a 10 nV sine
wave at 10 kHz. Clearly some amplification is required to
bring the signal above the noise. A good low-noise amplifier ref
will have about 5 nV/Hz of input noise. If the amplifier Lock-in
bandwidth is 100 kHz and the gain is 1000, we can expect our
output to be 10