12
Audio Guide Texas Instruments 1Q 2012
Audio Amplifiers
Design Considerations for Microphone Preamplifiers
Control Methods: Analog vs. Digital
r Analog control microphone preampli-
fiers typically use a variable resistor
on a product’s front panel that can be
changed during performance.
r Digitally-controlled microphones are
remotely controllable and have easily
recallable settings, offering significant
advantages when compared to their
analog control counterparts.
r In the live sound and recording indus-
try, digitally controlled microphones
allow signals to be preamplified and
converted closer to the source rather
than sending tiny μV signals across
meters of cable.
Equivalent Input Noise (EIN)
Considerations
r EIN is a key specification in defining
a microphone preamplifier.
r At a given gain, microphone
preamplifiers exhibit a certain amount
of input noise that is amplified
together with the audio source.
r Ideally, microphone preamplifiers will
have low EIN values to ensure that
only the audio source is amplified
instead of the noise.
Outputs: Differential vs.
Single-Ended
r Inside a product, a single-ended
output is sufficient to process signals
needing further processing.
r Many high-performance ADCs
require differential inputs. If the
amplified differential microphone
signal is taken directly to an ADC, a
differential output will give an
additional 6 dB of dynamic range.
r Differential outputs from a microphone
preamplifier will help ensure that the
differential input on the receiver
will reject any common-mode
interference induced on the cable by
cancelling out the common noise on
both connections.
Microphone Preamplifiers
For a complete list of Microphone Preamplifiers, see page 35.
For the latest information on audio end-equipment system block diagrams, visit www.ti.com/
audio
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35
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2012
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