Panasonic EB-X400 Service Manual page 15

Transmitter Description
The main block for the dual-band transmitter is also the Transceiver IC U101 RF chipset.
The Transceiver IC U101's modulator is a direct-conversion architecture, so there are no Tx IF frequencies.
The Transceiver IC U101 contains the following Tx blocks:
8 Dual-band (EGSM900/DCS1800) IQ modulators with outputs at final frequencies, and integrated IQ uplink low pass filters.
8 Open collector outputs to the rest of the Tx chains.
The open collector outputs of transceiver U101 are fed via internal H3 filter before application to the dual band inputs of Limiter
U102. The function of U102 is to reduce the AM ripple from the I, Q modulators.
The 900 MHz output signal from the Tx Limiter U102 must pass through a Tx SAW filter FL102 before entering into the PA
Module U103 in order to ensure Tx noise in Rx-band satisfy GSM specifications. For 1800 MHz, the 11.10 specifications are
not very severe, so no SAW filtering is needed here. The signals are then attenuated through two attenuators to meet the drive
levels of the PA Module U103. Power control is managed through the control line PALEVEL.
Harmonics in the PA output signal are attenuated by low-pass filters inside the Front-End Module.
Synthesiser Description
A synthesiser is provided in transceiver IC U101. The internal VCO operates from 3.42 GHz to 3.98 GHz, thus it is equivalent to
2 and 4 times of the DCS and EGSM frequencies. The registers, counters and phase detectors for this synthesiser are included
in the transceiver IC U101.
To meet GPRS lock-up timing requirement, provides a switched frac-N and integer-N counter. It also provides switched
bandwidth loop filter.
The TCXO module U301 generates 26 MHz in order to provide the reference clock to the transceiver IC and base-band portion.
Baseband circuits provide an automatic frequency control (AFC) voltage to compensate for frequency drift caused by
temperature variations.
Moreover, there is a thermistor RT101 which is used for the temperature compensation of PA and the reported RSSI.
DC Power Supplies
The PA runs directly from the battery and consumes no current when not transmitting. Two regulated 2.8 V lines
(RF2V8, VCC_VCXO) are provided for the rest of the RF circuitry from the U2006.
Antenna
Fixed helical typed antenna is utilised for EB-X400. Its length is 16 mm and located at the top of the lower unit.
It covers 900 MHz and 1800 MHz.
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