Samsung STH-N271 Service Manual page 65

STH-N271
Circuit Description
The IFC (U101) is mainly consist of IF interface part and AUDIO CODEC part. The IF interface part, witch is
between RF part (mainly U304) and BEC, translate RF data to baseband data for BEC. Mainly, IF interface part
is consist of receiver, transmitter, and some kind of RF control. The IFC also provides several A/D inputs to
monitor system parameters. Battery voltage is periodically measured after scaling via a resistor divider
(BAT_MON: U101_67). A thermistor located near the PA is monitored to obtain temperature status by
TMP_MON (U101_66). Finally, a voltage level from the battery case, identifying the type of battery, is measured
by AUX_MON (U101_65).
Receiver Interface
The U101 receive differential I/Q signals (RX_IN, RX_I, RX_QN, RX_Q: U101_48,49,50,51), or DEMOD signal
(U101_52) which come from RF demodulator (U304_11,12,9,10,16), and translate as digital data. These data is
synchronized by control signals (RX_SYNC, RX_CLK, and BBCLK: U101_31,32,40) is transported to BEC
through RX_DATA (pin U101_30). In addition, the U101 uses AGC_OUT (U101_72) for dynamic range of
receiver signal strength connected to U304_17, AFC_OUT (U101_71) for adjusting reference frequency exactly
connected to TXCO (OSC302_1).
Transmitter Interface
The U101 receives TX_DATA1 (U101_36) synchronized by control signals (TX_SYNC, TX_CLK: U101_33,34),
which come from BEC, and translate this data as differential I/Q signals (TX_IN, TX_I, TX_QN, TX_Q :
U101_61,60,58,57), or MOD signal (U101_63). It transport this data to RF modulation part. In addition, the U101
uses PA_CNT (U101_73),TX_PWR (U101_68) for controlling power of transmitter.
AUDIO CODEC
Three audio paths are implemented in IFC. The primary path utilizes the microphone (U101_11,12) and speaker
(U101_77,79), located on board. Both microphone and speaker utilize the main differential circuits in the IFC to
minimize noise pickup. The speaker output is amplified internally to enable direct connection to the speaker.
The second audio path connects to the headset jack. The headset microphone and speaker are passed to the
IFC's auxiliary input (U101_5) and output (U101_2), respectively. The headset jack terminals indicate via the
HS_SENSE (U115_4) to GPIO of BEC (U203_C11) when the headset is present. As well as when the headset
button is pushed via the SEND_END (U115_6) to GPIO of BEC (U203_A13). The third audio path to the HFK
shares the auxiliary output with the headset for its speaker and uses the second auxiliary input for its
microphone. Since the auxiliary output is not internally amplified, an external audio amplifier (U102) is applied
before connection to the headset and HFK.
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