D.baseband Output D.c. Offset Correction; E.receiver Local Oscillator (Lo) Generator; Transmitter Part - LG KG110 Service Manual

3. TECHNICAL BRIEF
The external capacitor is not required with ADI baseband ICs. The on chip filter has an auto
calibration feature ensuring that the filters are tuned for optimum performance. The baseband
amplifiers have programmable gain for system AGC.
A total of 57 dB of gain control is provided in 3dB steps programmable over the serial
interface. This together with the LNA gain control gives a total of 77dB of gain control range.
The receive baseband outputs are routed to the common Rx/Tx I/Q ports for connection with
the baseband converters.
D. Baseband Output D.C. Offset Correction
In order to minimize D.C. offsets inherent in the receiver and maximize dynamic range
a D.C offset correction circuit is integrated. This correction is triggered over the serial bus
and then an offset tracking loop is enabled to minimize residual offsets under all conditions.
The tracking loop is fully hardware integrated, requiring no software intervention.
E. Receiver Local Oscillator (LO) Generator
The Rx LO generator is used to avoid DC offset problems associated with LO leakage
into the receiver RF path. By operating the VCO at a frequency other than the desired
receive frequencies,any leakage of the VCO (e.g. via package) will fall out of band.
The LO generator is used to convert the offset synthesized VCO output to the
on-frequency quadrature LO required by the chipset.
The LO generator is implemented as a regenerative frequency divider, performing a 2/3
multiplication of the VCO output for the high band (DCS1800/PCS1900) and a 1/3
multiplication for low band (E-GSM/GSM850).

3.2.2 Transmitter Part

The Transmitter part contains AD6548 active parts and PAM .
The transmit section of the AD6548 radio implements a translation loop modulator.
This consists of a quadrature modulator, high speed phase-frequency detector (PFD) with
charge pump output, loop filter, TX VCO and a feedback down converting mixer.
The VCO output (divided by 2 for low band) is fed to the power amplifier with a portion
internally fed back into the down-converting feedback mixer to close the feedback loop.
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