Quadrature Amplitude Modulation Block Diagram | New Topic

In this note, we are going to know about the Quadrature Amplitude Modulation Block Diagram. Welcome to Poly Notes Hub, a leading destination for engineering notes for diploma and degree engineering notes.

Author Name: Arun Paul.

What is Quadrature Amplitude Modulation or QAM?

Amplitude modulation (AM) and phase modulation (using sine and cosine carriers) are combined in quadrature amplitude modulation (QAM). To improve the efficiency of data transmission, it is extensively utilized in digital telecommunications systems such as cable modems, DVB, LTE, and Wi-Fi.

I stands for in-phase, and Q for quadrature, and both are modulated onto carriers that are 90 degrees out of phase in QAM. After that, these two signals are joined and sent as one.

Key features of Quadrature Amplitude Modulation

• It combines amplitude and phase variations.
• QAM transmits multiple bits per symbol.
• Examples: 16-QAM (4 bits/symbol), 64-QAM (6 bits/symbol), 256-QAM (8 bits/symbol), etc.

Applications of QAM or Quadrature Amplitude Modulation

• This technique used in cable television.
• Also use in internet transmission system.
• Mobile communication like 4g/5g.
• Used in digital video broadcasting.
• Used in Wi-Fi standards (e.g., 802.11ac uses up to 256-QAM).

Quadrature Amplitude Modulation Block Diagram

Here we will explain the block diagram of QAM or Quadrature Amplitude Modulation technique –

• Input Data: Input data refers to the binary bits that will be transferred. These bits are organized into symbols that indicate amplitude and phase combinations in the QAM constellation.
• Serial to Parallel Converter: This block divides the incoming serial bitstream into two components: in-phase (I) and quadrature (Q), allowing for simultaneous modulation on orthogonal carriers and efficient data transfer in QAM.
• Digital to Analog Converter: The DAC or Digital to Analog Converter converts digital I and Q data streams to continuous analog waveforms. These analog signals can be processed and modulated onto carrier frequencies during the transmission path.
• Pulse Shaping Filter: Pulse shaping filters smoothen the I and Q signals to limit bandwidth and reduce inter-symbol interference (ISI), ensuring better signal quality and compatibility with channel bandwidth limitations.
• Carrier Generators: These generate sinusoidal carrier signals: cosine for the I path and sine (90° phase-shifted) for the Q path, which allows orthogonal modulation and efficient use of spectrum.
• Multipliers: Each analog signal (I and Q) is multiplied with its respective carrier wave. This step modulates both signals onto their carriers while preserving orthogonality and enabling simultaneous transmission.
• Adder: The final step in the transmitter, this unit adds the modulated I and Q signals together, producing the QAM waveform that carries both amplitude and phase information for transmission.