Sony Ericsson STICK MICRO W995 Troubleshooting Manual Download Page 98

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W995

1230-1858 rev. 1

FUNCTIONAL OVERVIEW

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generated from this clock. However, when audio is transferred between the application

and the access subsystems, the MCLK is used.

Master Clock
(26 MHz)

The 26.00 MHz VCXO-based MCLK is distributed as a square wave signal from the

GSM/EDGE circuit. In order to have full control over the load on the MCLK, only the access

side of the digital baseband controller is allowed to request the MCLK. However, by

indirect means also the application side CPU can issue the request. A VCXO-based square

wave is also distributed to the WCDMA circuit, but is turned on only upon a command

from the digital baseband controller.

Real-time Clock

(32. 768 kHz)

A 32.768 kHz crystal oscillator provides a low frequency clock whenever the platform has

power. This clock is used to keep the Real-Time Clock (RTC) block functioning, so that the

platform can keep track of the time and date. The low frequency clock is generated in the

analog baseband controller and distributed to the digital baseband controller, and if

necessary to external devices like Bluetooth, FM radio and A-GPS.

A-GPS

The Assisted GPS functionality in the phone is realized with the Global Locate

Hammerhead GPS module. The Global Locate Hammerhead belongs to the Type 2 GPS

solutions. The PMB 2525 Hammerhead II GPS IC is a GPS single chip device containing a

complete radio frequency front-end as well as the signal processing functionality in a

single die. The device allows the usage of assistance data by supporting A-GPS (assisted

GPS) standards (RRLP, RRC, OMA SUPL). One of three serial interfaces, UART, I²C or SPI,

is used for communication with the host system.

Clock Reference Frequency

The platform provides two reference frequencies, a 32.768 kHz clock (RTCCLK) from the
Analog Baseband Controller, and a 26 MHz reference clock (SYSCLK) from the Digital

Baseband Controller. The RTCCLK is used by the phone real time clock function. The
RTCCLK is distributed to the A-GPS module as a logical square wave. SYSCLK is derived

from the reference modulation clock MCLK to the platform access system and is
distributed from the Digital Baseband Controller to the A-GPS module. This 26 MHz clock

is synchronized with the cellular network to an accuracy of ±0.1 ppm. Automatic

frequency updates can also cause large frequency corrections, with associated phase
discontinuities. In order to isolate the A-GPS module for the unstable effects of SYSCLK,

an external reference clock is required. This external reference frequency provided by a
TCXO is required to provide a clock with very high short term stability. The frequency of

the TCXO is calibrated against the cellular reference clock by the A-GPS module enabling
the use of a more economical less accurate TCXO.

Interface and Control

The Interface and control consists of system timing and control. The control interface

includes a communication link where both data and control information are transferred

between platform and the A-GPS module. Data and command information is transferred

using a full-duplex Universal Asynchronous Receiver Transmitter (UART) interface.

Other control signals include the following:

• A GPIO or platform reset used as a reset signal (nRESET) to the GPS module.
• A Transmission On signal (TXON/ RX_HOLD), is used to indicate to the A-GPS module

when the ME is transmitting. The A-GPS modules receiver is disabled whilst the ME is
transmitting.

• A hardware timing pulse (GPSSTART/SYNC) providing the A-GPS module with a

highly accurate timing reference. The A-GPS is able to accurately synchronize its
GPS time to this reference pulse.

• A GPIO used as an enable (POWERON) signal to the GPS module.
• A GPIO used for power control for the GPS module.

A-GPS Block Diagram:

WLAN (Wi-Fi)

This WLAN module is based on the new Marvell 88W8686 chipset. WLAN module is
designed to support IEEE 802.11a or 802.11g payload data rates of 6, 9, 12, 18, 24, 36,

48 and 54 Mbps, as well as 802.11b data rates of 1, 2, 5.5 and 11 Mbps. For security the
WLAN module supports the IEEE 802.11i security standard through implementation of the

Advanced Encryption Standard (AES)/Counter Mode CBC-MAC Protocol (CCMP), and Wired
Equivalent Privacy (WEP) with Temporal Key Integrity Protocol (TKIP) security mechanism.

For video, voice and multimedia applications the WLAN module supports 802.11e Quality

of Service (QoS). The 3-wire Bluetooth / WiFi co-existence interface is also supported. The
WLAN module has a fully integrated RF to baseband transceiver that operates in both the

2.4 GHz ISM radio band for 802.11g/b WLAN applications and 5 GHz UNII radio band for
802.11a WLAN applications. It contains all the circuitry to support both transmit and

receive operations. The integrated LNA and AGC on the receive path is seamlessly
controlled by baseband functions. Integrated transmitters up-convert the quadrature

baseband signal and the deliver the RF signals to external power amplifiers for 2.4 GHz

and 5 GHz radio band transmission. Local oscillator frequencies are generated by a fully
integrated programmable frequency synthesizer. The loop bandwith is optimized for phase

noise and dynamic performance and quadrature signals are generated on-chip.

BT/WLAN Co-existence

Standards bodies did not fully anticipate the range of scenarios in which WLAN and

Bluetooth would compete for the same spectrum therefore IEEE 802.11 (WLAN) and

Bluetooth use the same 2.4 GHz ISM frequency band (although they use different access

mechanisms). They also did not include comprehensive, robust, and cooperative

mechanisms in their respective standards to mitigate interference. Since no mechanism

for exchanging signal status information has been built into the two standards, the task of

minimizing interference must be accomplished by other means. Co-location refers to the

situation where both Bluetooth and WLAN are in functional mode, that is, they are both

fully radio operational, performing either transmission or reception activities (or ready to

do so immediately). They also either share an antenna or each module has its own