Sony Ericsson W995 Troubleshooting Manual page 98

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.
FUNCTIONAL OVERVIEW
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
antenna, on the same device. Because both Bluetooth and WLAN operate in the same
unlicensed ISM band (2.4GHz), steps are required to avoid disturbances and allow
coexistence. The HW solution is a single antenna controlled by an Antenna Switch with 3-
wired lines between WLAN Device and BT Device. The used algorithm to decision whether
SEMC Troubleshooting Manual
W995
1230-1858 rev. 1 98 (125)