Page 77 - Electrical Engineering Dictionary

bandgap reference a voltage reference hertz per kilometer. See also
based on the 1.205 V bandgap voltage of sil- bandwidth-distance product.
icon.
bandwidth efficiency the ratio of the
bandgap wavelength the optical wave- information rate in bits per second to the
length corresponding to a photon energy required bandwidth in hertz for any digital
equal to the bandgap energy. modulation technique.

bandwidthimprovement(BI) adBread-
bandlimited a waveform is described as
ing that is a comparison of the RF bandwidth
bandlimited if the frequency content of the
of a receiver to the IF bandwidth. Designated
signal is constrained to lie within a finite band
as BI, it is 10 log B rf /B if .
of frequencies. This band is often described
by an upper limit, the Nyquist frequency, as-
suming frequencies from DC up to his upper bandwidth-distance product a measure
limit may be present. This concept can be ex- of the information carrying capacity of an op-
tended to frequency bands that do not include tical fiber which emphasizes that the band-
width is a function of distance. For example,
DC.
an optical fiber with a specification of 500
MHz-km bandwidth-distance product would
bandwidth (1) the frequency range of
have a 500 MHz bandwidth over 1 km, a
a message or information processing system
50 MHz bandwidth over 10 km ora1GHz
measured in hertz.
bandwidth over 0.5 km. See also bandwidth,
(2) width of the spectral region over which
optical fiber.
an amplifier (or absorber) has substantial
gain (or loss); sometimes represented more
bang-bang control control action
specifically as, for example, full width at half
achieved by a command to the actuator that
maximum.
tells it to operate in either one direction or the
(3) the property of a control system or other at any time with maximum energy.
component describing the limits of sinu- Bang-bang control is an optimal or subop-
soidal input frequencies to which the sys- timal piecewise constant control whose val-
tem/component will respond. It is usually uesaredefinedbyboundsimposedontheam-
measured at the half-power points, which are plitude of control components. The control
the upper and lower frequencies at which the changes its values according to the switching
output power is reduced by one half. Band- function which may be found using Pontrya-
width is one measure of the frequency re- gin maximum principle. The discontinuity
sponse of a system, i.e., the manner in which of the bang-bang control leads to disconti-
it performs when sine waves are applied to nuity of a value function for the considered
the input. optimal control problem. Typical problems
(4) the lowest frequency at which the ra- with bang-bang optimal control include time-
tio of the output power to the input power optimal control for linear and bilinear control
of an optical fiber transmission system de- systems.
creases by one half (3 dB) compared to the
ratio measured at approximately zero mod- Bardeen, John (1908–1991) Born:
ulation frequency of the input optical power Madison, Wisconsin, U.S.A.
source. Since signal distortion in an opti- Bardeen is best known for his two Nobel
cal fiber increases with distance in an opti- Prizes. The first prize he received was in
cal fiber, the bandwidth is also a function of 1956 for his development at Bell Labs, along
length and is usually given as the bandwidth- with Walter Brattain and William Schockley,
distance product for the optical fiber in mega- of the first transistor. When the three applied

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