Amplitude modulation & demodulation
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This document discusses amplitude modulation and demodulation. It defines amplitude modulation as varying the amplitude of a carrier wave linearly with a message signal while keeping frequency and phase constant. Modulation is used to transmit signals over long distances and allow multiple signals over the same channel. Demodulation recovers the signal intelligence by reversing the modulation process through rectification and filtering. The document describes amplitude modulation and different types of AM demodulation techniques.
Amplitude modulation & demodulation
- 1. Amplitude Modulation and Demodulation By: Bikram Modak Department-Computer Science and Engineering Semester-4th Roll no.-11900115013 Registration no.-151190110013
- 2. Introduction • Modulation -In the modulation process, some characteristic of a high-frequency carrier signal (bandpass), is changed according to the instantaneous amplitude of the information (baseband) signal. -It is the simplest and earliest form of transmitters. • Why Modulation -Suitable for signal transmission (distance…etc). -Multiple signals transmitted on the same channel. -Capacitive or inductive devices require high frequency AC input (carrier) to operate. -Stability and noise rejection.
- 3. Amplitude Modulation • AMPLITUDE MODULATION is formally defined as a process in which the amplitude of the carrier wave c(t) is varied about a mean value linearly with a message signal m(t) keeping frequency and phase constant . 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -5 0 5 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -1 0 1 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 -1 0 1 • The AM signal • The Modulating signal • The Carrier signal ttmkAts cc cos1 tm tAtc cc cos
- 4. (cont.) 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -5 -4 -3 -2 -1 0 1 2 3 4 5 • The Envelope • The AM signal ttmkAts cc cos1 tmkAts c 1
- 5. Amplitude Sensitivity Modulation Index - The ratio between the amplitudes between the amplitudes of the modulating signal and carrier, expressed by the equation: c m E E m =
- 6. AM-Percentage Modulation Under modulated (<100%) Envelope Detector Can be used 100% modulated Envelope Detector Can be used Over Modulated(>100%) Envelope Detector Gives Distorted Signal
- 7. Examples An Example of message signal m(t) Waveform for Amplitude modulation of the message signal m(t)
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- 9. (Cont.) Applications. • Analog and digital • SONET OC-768 and SDH STM-256 transmissions • 40 & 50 Gb/s transponders • High-speed Internet routers • DWDM, high-speed Ethernet and TDM • High-speed test equipment Features. • High modulation bandwidth • Low drive voltage • Chirp <0.1 • High extinction ratio • Small footprint • Optional PIN diode for optical power monitoring and bias control • Covers C and L Band • GaAs technology
- 10. Demodulation Demodulation is the process of recovering the signal intelligence from a modulated carrier wave. This process, also called detection, is the reverse process of modulation.
- 11. Why Do we Need Demodulation? -The wireless signal consists of radio frequency (high frequency) carrier wave modulated by audio frequency (low frequency). -The diaphragm of a telephone receiver or a loud speaker cannot vibrate with high frequency. Moreover, this frequency is beyond the audible range of human ear. So, it is necessary to separate the audio frequencies from radio- frequency carrier waves.
- 13. IMPORTANCE OF RECTIFICATION AND DEMODULATION • The modulation enveloped on the positive and negative sides are 180o out of phase. • If rectification is not done, then after filtering, the positive and negative envelopes would cancel each other . • So, the original modulating signal cannot be recovered. Thus, rectification is necessary in demodulation.
- 14. Types of AM Demodulation The major types of AM demodulator are: • Diode AM detector: This is by far the simplest form of AM demodulator or detector, requiring just a semiconductor (or other form) of diode along with a capacitor to remove the high frequency components. It suffers from a number of disadvantages, but its performance is more than adequate for most applications including broadcast receivers where cost is a significant driver. • Synchronous AM detector: This form of AM detector offers a higher level of performance, but at the cost of considerably the use of considerably more components. This means that it is only used in receivers where the levels of performance are paramount and can justify the additional component costs.