LG KT520 Service Manual page 59

3. TECHNICAL BRIEF
3.3.4 Voice Call
A. Voice call Downlink Mode(Receiver, Speaker, Headset)
This section provides a detailed description of the Voice Call RX functions.
The voice decoder accepts a serial input stream of linear PCM coded speech. The receive bandpass
filter is the next step in the CODEC receive path. Following the filter is the DAC, followed by a PGA
enabling to adjust or trim the circuit in the product for different sensitivity of the earphone and spread in
the RX path. The final step in the receive path is the auxiliary output. The auxiliary audio amplifier is
intended to drive low impedance headphones. The earphone amplifier and the auxiliary audio outputs
can be powered down (muted) via I2C. Both the earphone driver and one of the auxiliary drivers can
simultaneously provide an output signal during voice decoding.
• Receiver Mode : BEARP/N Port → Receiver(32Ω)
• Loud Speaker / Video Telephony Mode : AB3000 SPK Amp → SPKR/N → AUDIO AMP(TPA6205)
• Headset Mode : Auxiliary audio amplifier → AUXO1/2 → AUDIO AMP(TPA4411) → Head Phone
LGE Internal Use Only
Figure 3-3-4. Voice call Downlink Scheme
→ Speaker(8Ω)
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