6881094C31-E November 16, 2006
Theory of Operation: VOCON Board 3-39
3.2.5.2 Transmit Audio Path (for kit NNTN5567A)
Refer to Figure 3-14. The single-ended internal microphone audio enters the VOCON board through
pin 8 of the M102 contact, and the internal microphone bias is set by circuitry that includes C550,
R550 and R552. The internal microphone signal is connected to the INT_MIC_P pin, which is the
input terminal on the Mako IC internal op-amp G1 after the signal is multiplexed. The gain of the G1
pre-amp is set to +15 dB, which is programmed by dual-core processor SPI lines.
The external microphone audio enters the VOCON board through the remote connector J102, pin13,
and the external microphone bias is set by circuitry that includes C551, R551 and R553. The
external microphone signal is connected to the EXT_MIC_P pin, which is an input terminal on the
Mako IC internal op-amp G1 after the signal is multiplexed. The gain of the G1 pre-amp is set to +15
dB, which is programmed by dual-core processor SPI lines.
The dual-core processor, through the SPI bus, programs a multiplexer internal to the Mako IC to
select one of the microphone signals. Then, the selected microphone signal goes through the G1
pre-amplifier stage and on to a programmable gain amplifier (G2) before it goes to the CODEC for A/
D conversion. The resulting digital data is filtered and sent to the DSP on the CODEC_TX line from
the Mako IC VC_TX3V pin. After additional filtering and processing, the DSP sends the data-out from
the STDB pin, labeled TX_SSI_DATA to the RF interface connector P201 pin 4 (TX_DATA), which is
connected to the DAC U203 on the transceiver board.
Figure 3-14. VOCON Transmit Audio Path
Internal Mic Bias
(C550, R550, R552)
and Input
INT_MIC_P
Internal Mic Bias
(C551, R551, R553)
and Input
EXT_MIC_P
MUX
Pre-amp
G1 Gain
= 15 dB
MAKO_CS
SPI_MISOB
SPI_MOSIB
SCKB
4
Patriot
SPIB
Patriot
SAP/ BBP
MAKO IC U501
Amp G2
Gain = -30
to 0 dB
CODEC
A/D 16-
Bit
CODEC_TX
CODEC_FSYNC
CODEC_DCLK
TX_SSI_FSYNC
TX_SSI_CLK
TX_DATA
3
HPF = 200 Hz
& LPF = 3.4
kHz cutoff
RF D/A
U203
(On RF Board)
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