Functional Description - Nokia RM-333 Service Manual

RM-333; RM-334; RM-335
FMTx 2.1 Technical Description
Glossary
AF Audio Frequency
RF Radio Frequency
FM Frequency Modulation
Tx Transmitter
Rx Receiver
FMTx FM Transmitter
LPD Low Power Device
LNA Low Noise Amplifier
LDO Low Drop Out regulator
Received Signal Strength Indicator
RSSI (same as RPS)
Received Power Scan (Same as
RPS RSSI)
QFN Quad Flat No-Lead
FMTx2.1 HW block
The FMTx 2.1 implementation is based on the Silicon Laboratories Si4713 low power FM transmitter device.
This device has some state of the art features which have been utilised in the Nokia implementation. Apart
from having excellent RF transmitter performance and exceptional AF performance the device offers a number
of unique features, including the ability to retune the output stage of the device to ensure optimal matching
between the Tx antenna and the output stage of the device.

Functional description

The FMTx 2.1 solution comprises of the Si4713 device and ten external components. These components
consist of:
• A filter - an inductor and a varistor for filtering of emissions from the chip
• ESD protection - a resistor and diode package
• A dual capacitor package which is connected to the analogue audio input pins LIN & RIN. The fundamental
purpose of these capacitors is as DC blocking caps
• A filter on the reset line comprising a capacitor and a resistor
• An antenna which also provides the inductive load required by the Si4713 device
The Si4713 device is in a 3 x 3mm 20 pin QFN package.
Current implementations make use of the DAC33 device which allows data to be digitally clocked into the
DAC at high data rates, buffered and then streamed out at the correct rate while the rest of the baseband is
put to sleep in order to save power. This solution significantly increases playback time of audio content.
The Si4713 device has the following features:
• 88.1MHz – 107.9MHz FM band support.
• Programmable pre-emphasis (50/75us).
• Analogue audio interface
• Audio silence/signal present detection.
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