LG KG320, Руководство по обслуживанию

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3. TECHNICAL BRIEF
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The ADC output is downconverted to baseband with a digital quadrature local oscillator signal. Digital
decimation and FIR filters perform digital filtering, and remove ADC quantization noise, blockers, and
reference interferers. The response of the FIR filter is programmable to a flat pass band setting (FILTSEL =
0, Register 08h) and a linear phase setting (FILTSEL = 1, Register 08h). After filtering, the digital output is
scaled with a PGA, which is controlled with the DGAIN[5:0] bits in Register 20h.
The LNAG, AGAIN[2:0], and DGAIN[5:0] register bits should be set to provide a constant amplitude signal to
the baseband receive inputs. See “AN153: Aero II Transceiver AGC Strategy” for more details. Digitalto-
analog converters (DACs) drive differential I and Q analog signals onto the BIP, BIN, BQP, and BQN pins to
interface to standard analog-input baseband ICs.
The receive DACs are updated at 1.083 MHz and have a first-order reconstruction filter with a 1 MHz
bandwidth. No special processing is required in the baseband for dc offset compensation. The receive and
transmit baseband I/Q pins are multiplexed together in a 4-wire interface (BIP, BIN, BQP, and BQN). The
common mode level at the receive I and Q outputs is programmable with the DACCM[1:0] bits, and the full
scale level is programmable with the DACFS[1:0] bits in Register 05h.
(2) Transmit section
The transmit section consists of an I/Q baseband upconverter, an offset phase-locked loop (OPLL), and two
50 Ω output buffers that can drive an external power amplifier (PA). One output is for the GSM 850 (824-
849 MHz) and E-GSM 900 (880-915 MHz) bands and one output is for the DCS 1800 (1710-1785 MHz) and
PCS 1900 (1850-1910 MHz) bands.
The OPLL requires no external filtering to attenuate transmitter noise and spurious signals in the receive
band, saving both cost and power. The output of the transmit VCO (TXVCO) is a constant-envelope signal
that reduces the problem of spectral spreading caused by non-linearity in the PA. Additionally, the TXVCO
benefits from isolation provided by the transmit output buffers. This significantly minimizes any load pull
effects and eliminates the need for off-chip isolation networks.
A quadrature mixer upconverts the differential in-phase (BIP, BIN) and quadrature (BQP, BQN) baseband
signals to an intermediate frequency (IF) that is filtered and which is used as the reference input to the
OPLL. The OPLL consists of a feedback mixer, a phase detector, a loop filter, and a fully integrated
TXVCO. Low-pass filters before the OPLL phase detector reduce the harmonic content of the quadrature
modulator and feedback mixer outputs.
The transmit I/Q interface must have a non-zero input no later than 94 quarter bits after PDN is asserted for
proper operation. If the baseband is unable to provide a sufficient TX I/Q non-zero input preamble, then the
CWDUR bits in Register 05h can be used to provide a preamble extension.
The receive and transmit baseband I/Q pins are multiplexed together in a 4-wire interface (BIP, BIN, BQP,
and BQN). In transmit mode, the BIP, BIN, BQP, and BQN pins provide the analog I/Q input from the
baseband subsystem. The full-scale level at the baseband input pins is programmable with the BBG[1:0]
bits in Register 05h. The I and Q signals are automatically swapped within the Aero II transceiver when
switching bands. The transmit output path is automatically selected by the ARFCN[9:0] bits and the
BANDIND bits in Register 21h. As an option for multislot applications, direct control of the output transmit
buffers during a burst is offered through the PDTXO bit in Register 23h.