Only For Training And Service Purposes - LG KF305 Service Manual

Analog Input AIN1, AIN2 and VMIC configurations can be chosen by setting bits AudIS[3:0] in the
AudControl2 register (0x1E ). Additional gain of 9dB can be inserted into Analog Audio Input signal
chain by setting AudPreampGainSel bit high in the AudControl3 register (0x32 ).
Microphone Interface
The microphone pre-amplifier and associated integrated resistors support electret microphones. An
internal (Configuration 11) or external (Configuration 01 or 10) load resistor converts the current input
of the microphone to a voltage signal which is amplified using a low-noise pre-amplifier. The
Microphone signal path also includes an additional programmable gain of +9 dB gain directly after the
pre-amplifier. Different microphones require different DC bias currents for optimum sensitivity.
Audio ADC and PGA
The Audio ADC is a high-order single-bit sigma-delta ADC that includes a switchedcapacitor PGA at
the input.
Digital Filters
The AD6855 Audio Section provides two digital filters. The voiceband filter is used for applications with
a 8 kHz digital sample rate. The high-quality audio filter is used for applications with higher digital
sample rates.
Audio Accessory Detection
The AD6855 provides for detection of audio headset accessory insertion, extraction, and hookswitch
events. The detector circuit is designed to operate with minimum power in standby mode. There are
two pins dedicated to the accessory detector. AccDet is intended to interface to the external
microphone and monitor its bias voltage. The ACCDET terminal is used to sense hookswitch events
while a headset accessory is inserted. The JackSense terminal is interfaced to the switch pin of the
Jack socket or a Jack Sense terminal on a handset system connector.
Copyright © 2009 LG Electronics. Inc. All right reserved.

Only for training and service purposes

3. TECHNICAL BRIEF
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LGE Internal Use Only