During the past decade, many wireless communication techniques have been
developedto achievevariousgoals suchas higherdata rate,morerobustlink quality,
and higher number of users in a given bandwidth. For wireless communication
systems, depending on the availability of a feedback link, two approaches can be
considered: namely open and closed loop. Open loop communication system that
does not exploit the channel knowledge at the transmitter is now well understood
from both a theoretical and practical point of view.
Striking developments have taken place since 1980 in feedback control theory. The subject has be-
come both more rigorous and more applicable. The rigor is not for its own sake, but rather that even
in an engineering discipline rigor can lead to clarity and to methodical solutions to problems. The
applicability is a consequence both of new problem formulations and new mathematical solutions
to these problems. Moreover, computers and software have changed the way engineering design is
done. These developments suggest a fresh presentation of the subject, one that exploits these new
developments while emphasizing their connection with classical control.
Abstract: Transimpedance amplifiers (TIAs) are widely used to translate the current output of sensors like photodiode-to-voltagesignals, since several circuits and instruments can only accept voltage input. An operational amplifier with a feedback resistor fromoutput to the inverting input is the most straightforward implementation of such a TIA. However, even this simple TIA circuit requirescareful trade-offs among noise gain, offset voltage, bandwidth, and stability. Clearly stability in a TIA is essential for good, reliableperformance. This application note explains the empirical calculations for assessing stability and then shows how to fine-tune theselection of the feedback phase-compensation capacitor.
Photodiodes can be broken into two categories: largearea photodiodes with their attendant high capacitance(30pF to 3000pF) and smaller area photodiodes withrelatively low capacitance (10pF or less). For optimalsignal-to-noise performance, a transimpedance amplifi erconsisting of an inverting op amp and a feedback resistoris most commonly used to convert the photodiode currentinto voltage. In low noise amplifi er design, large areaphotodiode amplifi ers require more attention to reducingop amp input voltage noise, while small area photodiodeamplifi ers require more attention to reducing op amp inputcurrent noise and parasitic capacitances.
The equal-area theorem●This is sinusoidal PWM (SPWM)●The equal-area theorem can be appliedto realize any shape of waveforms
●Natural sampling●Calculation based on equal-area criterion●Selected harmonic elimination●Regular sampling●Hysteresis-band control●Triangular wave comparison withfeedback control
