Complex Waves

Complex waves include:

• Analog modulated, digitally modulated, pulse-width
• modulated, and quadrature modulated signals
• Digital patterns and formats
• Pseudo-random bit and word streams

Quadrature Modulation

In Signal Modulation waves the amplitude, phase and/or frequency variations embed lower-frequency information into a carrier signal of higher frequency. It gives signals in the form of either speech, data or video. In Analog Modulation the signal varies the carrier’s amplitude and/or frequency. At the receiving end, demodulating circuits interpret the amplitude and/or frequency variations, and extract the content from the carrier. Phase modulation modulates the phase rather than the frequency of the carrier waveform to embed the content. Digital modulation is based on two states which allow the signal to express binary data. In amplitude-shift keying (ASK), the digital modulating signal causes the output frequency to switch between two amplitudes; in frequency-shift keying (FSK), the carrier switches between two frequencies (its center frequency and an offset frequency); and in phase-shift keying (PSK), the carrier switches between two phase settings. In PSK, a “0” is imparted by sending a signal of the same phase as the previous signal, while a “1” bit is represented by sending a signal of the opposite phase. Pulse-width modulation (PWM) is another common digital format; it is often used in digital audio systems. It is applicable to pulse waveforms only. With PWM, the modulating signal causes the active pulse width (duty cycle, explained earlier) of the pulse to vary. Quadrature (IQ) modulation technology is used for building digital wireless communications networks. An in-phase (I) waveform and a quadrature-phase (Q) waveform that is delayed by exactly 90 degrees relative to the “I” waveform are modulated to produce four states of information. An in-phase (I) waveform and a quadrature-phase (Q) waveform are combined and transmitted over one channel, then separated and demodulated at the receiving end. The IQ format delivers far more information than other forms of analog and digital modulation  because it increases the effective bandwidth of the system. A digital pattern consists of multiple synchronized pulse streams. It makes up words of 8, 12, 16, or more bits wide data. The digital pattern generator, specializes in delivering words of data to digital buses and processors via parallel outputs. Digital computers have the inability to produce truly random numbers, therefore Pseudo-random bit streams (PRBS) and pseudo-random word streams (PRWS) are used. Digital video signals can have jagged lines on surfaces that should be smooth. Controlled amount of noise is added to hide these jagged lines from the eye without losing the original information. Serializers or multiplexers are tested using PRWS.

Phase

Inorder to understand Phase, consider a sine wave. The voltage level of sine waves is related to circular motion. One cycle of a sine wave travels through 360 degrees. Phase shift (also known as delay), describes the difference in timing between two signals. Phase is usually expressed in degrees but a time value may be more appropriate in some circumstances. The phase angle of a sine wave shows how much time it has passed. Two waveforms can have similar frequency and amplitude but they may differ in phase. Two waves may be similar in other ways, but the Phase shift describes the time difference or the delay in the waves.

Phase Shift or Delay

Waveform

According to an English dictionary a waveform is a usually graphic representation of the shape of a wave that indicates its characteristics (as frequency and amplitude).

A waveform is a representation of how alternating current (AC) varies with time, e.g., sine wave. The sine wave represents energy entirely concentrated at a single frequency. An ideal, unmodulated wireless signal has a sine waveform, with a frequency usually measured in megahertz (MHz) or gigahertz (GHz). 

A wave is a pattern of varying quantitative values that repeats over a certain interval of time. They are a periodically repeating phenomena. Signal generators produce electrical (voltage) waves that repeat in a controllable manner. A full repetition of a wave is called a cycle. Waveform graphically represents the activity of the wave and any change in it overtime. Some of the characteristics of waveforms are Amplitude, Frequency, and Phase. Amplitude of a wave measures the strength of the wave from the lowest point that a wave hits to the highest point. In other words it is the maximum disturbance (of a wave) from its undisturbed position. Frequency is the rate at which waveform cycles occur while phase is the time placement of a cycle relative to a reference waveform or point in time.