IQ Modulator/Demodulator

2006-12-06 By 小宗宗

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ModulationModulation is a higher frequency carrier signal carry a lower frequency message signal in a receiver and discard the carrier signal to get the original message signal in the demodulator.

There are three ways for digital information to be carried.Using amplitude shifting (AM)Using frequency shifting (FM)Using phase shifting (PM)

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Three types of modulation

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Polar coordinate systemThese two representations are equivalent and contain the exact same information, just in different forms.

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Using the trigonometry to proof the I/Q equation

I=Amplitude of the “In-Phase Carrier”Q=Amplitude of the “Quadrature-Phase Carrier”

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Block diagram of an IQ modulator

What is the advantages of I/Q modulation?

Hardware circuit is easy to design.

More flexible.

Quadrature Phase Shift Keying (QPSK)

QPSK IQ Diagram

Non-return-to-zero (NRZ)

QPSK Modulator

QPSK Demodulator

Matlab Simulation

Block diagram of Modulator

The scopes of each point

The scopes of each point (continue)

Block diagram of demodulator

The scopes of each point

The scopes of each point (continue)

The scopes of each point (continue)

Fin