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Circuit Description
2-2
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2) TX PART
Baseband IQ signal fed into offset PLL, this function is included inside of U801 chip. The transmit section of U801
consist of an I/Q baseband upconverter, an offset phase-locked loop (OPLL) and two 50 ohm output buffers that can drive
an external Power Amplifier(PA). Si4210 chip generates modulator signal which power level is about 1.5dBm and fed into
Power Amplifier(U900). The PA output power and power ramping are well controlled by Auto Power Control circuit.
We use offset PLL below.
Modulation Spectrum
200kHz offset
30 kHz bandwidth
GSM
-35dBc
DCS
-35dBc
PCS
-35dBc
400kHz offset
30 kHz bandwidth
GSM
-66dBc
DCS
-65dBc
PCS
-66dBc
600kHz ~ 1.8MHz offset
30 kHz bandwidth
GSM
-75dBc
DCS
-68dBc
PCS
-75dBc
2. Baseband Circuit description of SGH-X480,SGH-X480C,SGH-X488
1) CSP2200B1
1. Power Management
Seven low-dropout regulators designed specifically for GSM applications power the terminal and help ensure optimal
system performance and long battery life. A programmable LDO provides support for 1.8V, 3.0V SIMs, while a
self-resetting, electronically fused switch supplies power to external accessories. Ancillary support functions, such as two
LED drivers and two call-alert drivers, aid in reducing both board area and system complexity. A four-wire serial interface
unit(SIU) provides access to control and configuration registers. This interface gives a microprocessor full control of the
CSP2200B1 and enables system designers to maximize both standby and talk times. Error reporting is provided via an
interrupt signal and status register. Supervisory functions. including a reset generator, an input voltage monitor, and a
thermal monitor, support reliable system design. These functions work together to ensure proper system behavior during
start-up or in the event of a fault condition(low microprocessor voltage, insufficient battery energy, or excessive die
temperature).
2. Battery Charge Management
A battery charge management block, incorporating an internal PMOS switch, and an 8-bit ADC, provides fast, efficient
charging of single-cell Li-Ion battery. Used in conjunction with a current-limited voltage source, this block safely
conditions near-dead cells and provides the option of having fast-charge and top-off controlled internally or by the system's
microprocessor.
