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3. Technical Brief
The voice decoder accepts a serial input stream of linear PCM coded speech. The receive band-pass
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 earphone amplifier and 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 : Earphone amplifier → BEARP/N Port → Receiver(32Ω)
• Loud Speaker / Video Telephony Mode : Auxiliary audio amplifier → AUXO1/2 →
• Headset Mode : Auxiliary audio amplifier → AUXO1/2 → SURROUND AUDIO PROCESSOR
(NJM2705) → TJATTE2 → Analog S/W(NLAS4684) →
HEADSET AMP(LM4809LD) → Head Phone
Loud Speaker Mode has four GPIO switching control ports. It is 3D_CTRL1/2, HS_SPK_SEL and
Audio_AMP_EN. HS_SPK_SEL controls analog switch(NLAS4684) and Audio_AMP_EN controls
shutdown of AUDIOAMP(LM4809LD). Video Telephony Mode has same paths with Loud Speaker
Mode.
Mode
Receiver
Headset (amr)
Headset (mp3)
Loud Speaker, VT
3D Speaker (mp3)
SURROUND AUDIO PROCESSOR(NJM2705) →
TJATTE2 → Analog S/W(NLAS4684) →
AUDIO AMP(TPA2005D1) → Speaker(8Ω)
3D IC
3D_CTRL1
--
Low
High
Low
Low
Table 3-4-2. Speaker Phone Mode GPIO Control State
HS_SPK_SEL
3D_CTRL2
--
Low
Low
Low
High
- 60 -
AUDIO_AMP_EN
--
--
Low
Low
Low
Low
High
High
High
High
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