beautypg.com

Ensemble Designs BrightEye 46 3G/HD/SD/ASI Electrical to Optical Converter User Manual

Page 14

background image

www.ensembledesigns.com

BrightEye-14

3G/HD/SD/ASI Electrical to Optical Converter User Guide

TM

BrightEye 46

Optical

An optical interface between two devices carries data by modulating a light source. This light source

is typically a laser or laser diode (similar to an LED) which is turned on and off at the bitrate of the

datastream. The light is carried from one device to another through a glass fiber. The fiber’s core acts

as a waveguide or lightpipe to carry the light energy from one end to another. Optical transmission

has two very significant advantages over metallic copper cables. Firstly, it does not require that the

two endpoint devices have any electrical connection to each other. This can be very advantageous

in large facilities where problems with ground loops appear. And secondly, and most importantly, an

optical interface can carry a signal for many kilometers or miles without any degradation or loss in the

recovered signal. Copper is barely useful at distances of just 1000 feet.

Oversampling

A technique to perform digital sampling at a multiple of the required sample rate. This has the

advantage of raising the Nyquist Rate (the maximum frequency which can be reproduced by a given

sample rate) much higher than the desired passband. this allows more easily realized anti-aliasing

filters.

PAL

During the early days of color television in North America, European broadcasters developed a

competing system called Phase Alternation by Line. This slightly more complex system is better able

to withstand the differential gain and phase errors that appear in amplifiers and transmission systems.

Engineers at the BBC claim that it stands for Perfection At Last.

Progressive

An image scanning technique which progresses through all of the lines in a frame in a single pass.

Computer monitors all use progressive displays. This contrasts to the interlace technique common to

television systems.

Return Loss

An idealized input or output circuit will exactly match its desired impedance (generally 75 ohms) as a

purely resistive element, with no reactive (capacitive or inductive elements). In the real world we can

only approach the ideal. So our real inputs and outputs will have some capacitance and inductance.

This will create impedance matching errors, especially at higher frequencies. The Return Loss of

an input or output measures how much energy is returned (reflected back due to the impedance

mismatch). For digital circuits, a return loss of 15 dB is typical. This means that the energy returned is

15 dB less than the original signal. In analog circuits, a 40 dB figure is expected.

RGB

RGB systems carry the totality of the picture information as independent Red, Green, and Blue signals.

Television is an additive color system, where all three components add to produce white. Because the

luminance (or detail) information is carried partially in each of the RGB channels, all three must be

carried at full bandwidth in order to faithfully reproduce an image.