Question

In a lock-in amplifier, a mechanical chopper is often used. What are the two main purposes of the mechanical chopper?

Why is the modulated signal multiplied by the carrier wave in a lock-in amplifier? (be as detailed as possible)

Answer 1

Mechanical chopper is basically used to controll the light intensity . It restricts the path of te light intensity in many scientific technologies.These choppers are basically employed in those applications where manual restriction in the path of a light beam is requires. The basic example is Lock-in amplifier and Mouse used with a computing device.

The puspose of mechanical chopper are:

1. One of the application of chopper in electronics is to convert a fixed dc signal( voltage) into a variabe dc signal (voltage).
2. It is also widely used to suppress the effects of noise in an electronic device.

• A modulated signal in lock-in amplifier is multiplied by the carrier signal in order to get back the best possible output. Basically it reduces all the redundant components from the Unmodulated signal as well as reduces the frequency of the mudulated signal. An unmodulated signal when transmitted from one point to another points during amplification in a electronic device induces some noise factor. For exmaple, shot noise or johnsons noise which changes the composition and behaviour of the signal. To remove this redundanncy we must always multiply our modulated signals to the carrier signal.
• Also a modulated signals consists of very high frequency which creates some problem in further processing.Hence multiplying a modulated signal with carrier signal reduces frequency.

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