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Related Concept Videos

Time and frequency -Domain Interpretation of PI Control01:27

Time and frequency -Domain Interpretation of PI Control

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Proportional-Integral (PI) controllers are essential in many control systems to improve stability and performance. They are commonly used in everyday devices like thermostats to enhance system damping and reduce steady-state error. When the zero in the controller's transfer function is optimally placed, the system benefits significantly in terms of stability and accuracy.
Acting as a low-pass filter, the PI controller slows the system's response and extends settling times. This requires...
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Gain01:15

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Gain and phase shift are properties of linear circuits that describe the effect a circuit has on a sinusoidal input voltage or current. The circuit's behavior that contains reactive elements will depend on the frequency of the input sinusoid. As a result, it is observed that the gain and phase shift will all be frequency functions.
Gain:
Suppose Vin is the input and Vout is the output signal to a circuit.
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Phase-lead and Phase-lag Controllers01:22

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Understanding the working function of different types of controllers can be illustrated with practical analogies, such as adjusting a stereo's volume equalizer. Cranking up the bass involves a phase-lead controller, which functions as a high-pass filter, while increasing the treble uses a phase-lag controller, which acts as a low-pass filter. PD controllers, similar to high-pass filters, enhance the system's response to high-frequency components. PI controllers, akin to low-pass...
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Time and frequency -Domain Interpretation of Phase-lead Control01:24

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Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
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In the standard form, the transfer function is shown in constant gain, poles/zeros at origin, simple poles/zeros, and quadratic poles/zeros; each contributing uniquely to the system's overall response. The term represents the magnitude of the simple zero:
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Time and frequency -Domain Interpretation of Phase-lag Control01:21

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Phase-lag controllers are widely used in control systems to improve stability and reduce steady-state errors. A dimmer switch controlling the brightness of a light bulb serves as a practical example of phase-lag control, gradually adjusting the bulb's brightness. Mathematically, phase-lag control or low-pass filtering is represented when the factor 'a' is less than 1.
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Relation between vestigial-sideband filtering and pi/2 progressive phase shift.

Xing Wei1, Juerg Leuthold

  • 1Bell Laboratories, Lucent Technologies, Holmdel, New Jersey 07733, USA. xingwei@lucent.com

Optics Letters
|August 18, 2004
PubMed
Summary

This study reveals that Gaussian vestigial-sideband (VSB) return-to-zero (RZ) on-off-keying (OOK) signals are RZ OOK signals with a phase shift. This VSB signal characteristic reduces intersymbol interference through destructive interference.

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Area of Science:

  • Optical communications
  • Signal processing

Background:

  • Intersymbol interference (ISI) is a major limitation in high-speed optical communication systems.
  • Vestigial-sideband (VSB) modulation offers potential for improved spectral efficiency.
  • Return-to-zero (RZ) on-off-keying (OOK) is a common modulation format.

Purpose of the Study:

  • To characterize the nature of Gaussian-shaped VSB RZ OOK optical signals.
  • To explain the mechanism behind the reduced intersymbol interference in VSB signals.
  • To demonstrate a practical method for generating VSB signals at high data rates.

Main Methods:

  • Theoretical analysis of Gaussian VSB RZ OOK signals.
  • Experimental demonstration of VSB signal generation.
  • Utilizing a pi/2 progressive phase shift characterization.

Main Results:

  • Gaussian VSB RZ OOK signals are equivalent to RZ OOK signals with a pi/2 phase shift.
  • Reduced intersymbol interference in VSB signals is attributed to destructive interference.
  • An effective 40-Gbit/s VSB signal was generated without optical filter detuning.

Conclusions:

  • The pi/2 phase shift is key to the VSB RZ OOK signal's performance.
  • Destructive interference provides a physical explanation for ISI reduction.
  • The demonstrated method offers a filter-detuning-free approach to high-speed VSB signal generation.