Lock In Amplifier

A lock in amplifier is a type of amplifier that can extract a signal with a known carrier wave from an extremely noisy environment.

Lock in amplifier.

Noise signals at frequencies other than the reference frequency are rejected and do not affect the measurement. Lock in amplifiers are used to measure the amplitude and phase of signals buried in noise by using the process of synchronous detection to recover the signals. The amplifier achieves this by acting as a narrow bandpass filter that removes much of the unwanted noise while allowing through the signal that is to be measured. If the frequency of the desired signal is known the instrument can lock in onto the signal using a matching reference frequency.

Lock in amplifiers are used frequently in scientific experiments that require measuring small voltages in noisy environments. Lock in amplifiers use the knowledge about a signal s time dependence to extract it from a noisy background. A 1 second time constant. A lock in amplifier also known as a phase sensitive detector is a type of amplifier that can extract a signal with a known carrier from an extremely noisy environment it is basically an analog multiplier followed by a low pass filter practically a lock in amplifier convert the high frequency signal into a dc component or at a very low frequency.

The time constant is simply 1 2pf where f is the 3 db frequency of the filter. A lock in amplifier performs a multiplication of its input with a reference signal also sometimes called down mixing or heterodyne homodyne detection and then applies an adjustable low pass filter to the result. The dynamic reserve of a lock in amplifier at a given full scale input voltage is the ratio in db of the largest interfering signal to the full scale input voltage. Each instrument is equipped with the control software labone.

Lock in amplifiers recover signals in noisy backgrounds or give high resolution measurements of clean signals over several orders of magnitude and frequency. Lock in amplifiers have traditionally set the low pass filter bandwidth by setting the time constant. Lock in amplifiers use a technique known as phase sensitive detection to single out the component of the signal at a specific reference frequency and phase. The largest interfering signal is defined as the amplitude of the largest signal at any frequency that can be applied to the input before the lock in cannot measure a signal with.

The low pass filters are simple 6 db oct roll off rc type filters.