LG G7100, Руководство по обслуживанию

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In direct conversion receiver there is only one mixer down-converting received RF signal to BB signal
directly. The gain down converting mixer is 40dB at high gain mode and 22dB at low gain mode.
The Rx gain setting is done in the AGC algorithm. The nominal gain of the receiver is set as a
function of the expected signal strength at the antenna input so that a desired level is reached at the
Rx I/Q. 7 blocks in the receiver chain have variable gains, LNA, Mixer, LPF1, VGA1, gmC Filter,
Auxiliary gain control and VGA2. The gain settings can be adjustable via 3-wire bus control lines.
The baseband signals pass via integrated low-pass filters to the baseband A/D converters.
Theremainder of the channel filtering is performed by the baseband chipset. The demodulator
contains switches to maintain the sense of the baseband I/Q outputs with respect to the incoming RF
signal on both GSM900 and DCS1800.
Three correction loops ensure that DC offsets, generated in the CX74017, do not overload the
baseband chain at any point.
After compensation, the correction voltages are held on capacitors for the duration of the
receive slot(s). A rising edge on the RXEN signal, selected via the serial interface, placed the
DC compensation circuitry in the track mode.
B. Demodulator and baseband processing
C. DC offset compensation
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3. TECHNICAL BRIEF