LM3886_03 datasheet(22/24 Pages) NSC

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Definition of Terms (Continued)

applies with the output transistors conducting alternately at a

high enough frequency that the peak capability of neither

transistor is exceeded.

Power Bandwidth: The power bandwidth of an audio am-

plifier is the frequency range over which the amplifier voltage

gain does not fall below 0.707 of the flat band voltage gain

specified for a given load and output power.

Power bandwidth also can be measured by the frequencies

at which a specified level of distortion is obtained while the

amplifier delivers a power output 3 dB below the rated out-

put. For example, an amplifier rated at 60W with

≤ 0.25%

THD + N, would make its power bandwidth measured as the

difference between the upper and lower frequencies at which

0.25% distortion was obtained while the amplifier was deliv-

ering 30W.

Gain-Bandwidth Product: The Gain-Bandwidth Product is

a way of predicting the high-frequency usefulness of an op

amp. The Gain-Bandwidth Product is sometimes called the

unity-gain frequency or unity-gain cross frequency because

the open-loop gain characteristic passes through or crosses

unity gain at this frequency. Simply, we have the following

relationship: A

CL1 xf1 =ACL2 xf2

Assuming that at unity-gain (A

CL1 = 1 or (0 dB)) fu = fi =

GBWP, then we have the following: GBWP = A

CL2 xf2

This says that once fu (GBWP) is known for an amplifier,

then the open-loop gain can be found at any frequency. This

is also an excellent equation to determine the 3 dB point of a

closed-loop gain, assuming that you know the GBWP of the

device. Refer to the diagram on the following page.

Biamplification: The technique of splitting the audio fre-

quency spectrum into two sections and using individual

power amplifiers to drive a separate woofer and tweeter.

Crossover frequencies for the amplifiers usually vary be-

tween 500 Hz and 1600 Hz. “Biamping” has the advantages

of allowing smaller power amps to produce a given sound

pressure level and reducing distortion effects produced by

overdrive in one part of the frequency spectrum affecting the

other part.

C.C.I.R./A.R.M.:

Literally: International Radio Consultative Committee

Average Responding Meter

This refers to a weighted noise measurement for a Dolby B

type noise reduction system. A filter characteristic is used

that gives a closer correlation of the measurement with the

subjective annoyance of noise to the ear. Measurements

made with this filter cannot necessarily be related to un-

weighted noise measurements by some fixed conversion

factor since the answers obtained will depend on the spec-

trum of the noise source.

S.P.L.: Sound Pressure Level — usually measured with a

microphone/meter combination calibrated to a pressure level

of 0.0002 µBars (approximately the threshold hearing level).

S.P.L. = 20 Log 10P/0.0002 dB

where P is the R.M.S. sound pressure in microbars.

(1 Bar = 1 atmosphere = 14.5 lb/in

2 = 194 dB S.P.L.).

01183316

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