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What is homodyne and heterodyne detection?
The basic difference between Homodyne and Heterodyne Detection is based on the signal carrier and local oscillator frequency. In homodyne detection signal carrier and local oscillator frequency is equal i.e. ωif = 0 and In heterodyne detection signal frequency and carrier frequency are not equal i.e. ωif ≠0.
What does a lock-in detector do?
Lock-in amplifiers are used to detect and measure very small AC signalsall the way down to a few nanovolts. Accurate measurements may be made even when the small signal is obscured by noise sources many thousands of times larger.
What is the main attraction of the optical homodyne detection?
Explanation: The main attraction of optical homodyne detection is the potential 3dB improvement in the receiver sensitivity. It also eases the receiver bandwidth requirement considerably.
How does lock-in work?
Lock-in amplifiers use a technique known as phase sensitive detection to single out the component of the signal at a specific frequency and phase. Once it does this, noise signals at other frequencies or random phases are rejected through electronic (analog lock- in) or software (DSP lock-in) filtering.
What is lock sensitivity?
Here is the definition from the STS 830 manual: “The sensitivity of the lock-in is the rms amplitude of an input sine (at the reference frequency) which results in a full scale DC output. Traditionally, full scale means 10 VDC at the X, Y or R BNC output.
Why is direct detection so difficult?
Why is direct detection so difficult? Because exoplanets are so far away and therefore very dim. Also, their host stars outshine them. The planet or planets actually pass in front of the star (from our point of view).
What is the difference between coherent detection and direct detection?
Coherent detection is well known in wireless communication systems. In a direct detection receiver, its photo-detector only responds to changes in the receiving signal optical power, and cannot extract any phase or frequency information from the optical carrier.
How is homodyne detection used in Electrical Engineering?
In electrical engineering, homodyne detection is a method of extracting information encoded as modulation of the phase and/or frequency of an oscillating signal, by comparing that signal with a standard oscillation that would be identical to the signal if it carried null information.
What do you need to know about quadrature demodulation?
In quadrature demodulation, we are converting the existing modulation into the corresponding I/Q baseband signals. It’s important to understand that the received signal could be from any sort of transmitter—quadrature demodulation is not limited to signals that were originally created through quadrature modulation.
How does a quadrature modulator work in reverse?
You will readily notice that the system is similar to a quadrature modulator in reverse. The RF signal is multiplied by the local oscillator signal (for the I channel) and the local oscillator shifted by 90° (for the Q channel).
Why do we need low pass filters in a quadrature demodulator?
The low-pass filters are needed because the quadrature multiplication applied to the received signal is no different from the multiplication employed in, for example, an ordinary AM demodulator.