Bthfmtxrds3.0B Technical Description; Bthfmtxrds3.0B Functional Description; Block Diagram - Nokia RM-579 Service Manual

RM-578; RM-579
System Module

BTHFMTXRDS3.0b Technical Description

BTHFMTXRDS3.0b functional description

Bluetooth and FM radio receiver and transmitter are provided by the same ASIC. The device supports Bluetooth
2.1 + EDR (Enhanced Data Rate) and FM + RDS radio reception in both European/American and Japanese bands
(the appropriate region-specific FM radio band is pre-configured in the phone software). The FM transmitter
feature allows audio content stored in the phone (such as mp3 files) to be transmitted to a nearby FM radio
receiver (such as a car radio). The region-specific channels where FM transmitter operation is permitted are
pre-configured in the phone software.
The Bluetooth-FM device UART interface allows the device to communicate with the phone baseband engine
using Bluetooth HCI (Host Control Interface) commands. When Bluetooth is switched on, the phone user
interface the BT_RESETX line is toggled to reset the Bluetooth device, and commands are sent over the UART
interface to configure the device. If UART communication fails (due to a hardware fault) it will not be possible
to switch on Bluetooth or the FM radio receiver or transmitter from the phone user interface.
The device has two clock signals: SYS_CLK (19.2MHz, 26.0MHz, or 38.4MHz supported) and SLEEP_CLK (32.768
kHz). The SLEEP_CLK is supplied all the time the phone is switched on. To maximise the phone standby time,
it is only necessary to provide a SYS_CLK signal when Bluetooth activity occurs, such as sending Bluetooth
data to another device, or checking periodically if there are any other Bluetooth devices attempting to
communicate with it. At other times when the Bluetooth device is in standby mode or the FM receiver or
transmitter is switched on it is only necessary to provide a SLEEP_CLK signal. The Bluetooth-FM ASIC is powered
directly from the phone battery voltage line (VBAT). An internal regulator is enabled when Bluetooth or FM
radio is switched on.
Bluetooth audio signals are sent to and from the device using a PCM interface. The Bluetooth RF signal is
routed via a buried track to the Bluetooth antenna on the side of the PWB. An RF filter is needed between
the Bluetooth antenna and Bluetooth ASIC to prevent interference to and from the cellular phone antenna.
Phones that have both Bluetooth and WLAN use a shared antenna, as both services occupy the 2.4GHz ISM
frequency band. The co-existence signalling interface between Bluetooth and WLAN ASICs controls the RF
activity in the shared frequency band.
The audio signal from the FM radio receiver is routed via the phone Audio ASIC to the phone headset or
loudspeaker. The external wired headset is also used as an Antenna for the FM radio receiver. The FM radio
receiver RF signal is routed from the ASIC via a buried track to an impedance matching circuit placed near
the headset connector.
The audio input signal for the FM radio transmitter is provided by the phone baseband engine. The FM
transmitter uses a dedicated internal antenna (generally mounted in the phone mechanics) to radiate the
FM signal to a nearby radio receivers. Internal antenna is also used to perform a signal level scan of the FM
band to determine potential channels for FM transmission to reduce the effect of interference from other FM
transmitters.

Block Diagram

The following block diagram shows how Bluetooth-FM is connected to the host engine.
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