Service manual

7.Detailed description of Schematic Diagram
7.1 Transceiver
The main chip for Taichi RF is MAGIC. The MAGIC IC is intended to support
the needs of the GSM/DCS1800 portable telephone products.
For Taichi the MAGIC IC will provide the first LO (RX VCO) to the receiver at
1325.2 to 1359.8 MHz for EGSM with 400 MHz high side injection, and
1405.2 to 1479.8 MHz for DCS 1800 with 400 MHz low side injection. An
external RF mixer will convert the received signal to 400 MHz. The 400 MHz
signal will then pass through an external SAW filter. The filtered signal will
then enter the IC where it will be mixed with an internally generated 400 MHz
signal to generate baseband I and Q signals. These baseband signals will
then be filtered and amplified to provide RxI and Q. The RxI and Q signals will
be converted into digital outputs and sent over a serial bus. The chip will
provide for AGC control through the SPI bus. TX Data will be input serially.
The present data bit and the three previous data bits will be used to set up
one of 16 possible waveforms based on the sum of Gaussian pulses stored in
a look up ROM. The resulting signal will then be clocked out at a 16X
oversample rate. This data pattern will be input to a four accumulator
fractional N synthesizer with 24 bit resolution. The synthesizer output will be
880.2 to 914.8 MHz for EGSM and 1710.2 to 1784.8 MHz for DCS 1800 with
GMSK modulation and will be directly amplified to the transmitter output. The
reference oscillator will be a free running 26 MHz crystal for MAGIC. AFC will
be provided through the SPI bus as a programming offset to the fractional N
division system. Resolution will be approximately 3Hz (6 Hz with Pass 2) with
relative accuracy of less than 1Hz (2 Hz for Pass 2). Since the 26 MHz crystal
will not be locked to the AFC, a second fractional divider system will be
provided to derive an accurate 200kHz reference. This reference will then be
multiplied in a PLL to 13MHz for use as an accurate clock to the logic sections
of the radio.
Two tracking regulators will be provided to power the IC. A superfilter will also
be provided to power the external main VCO.
Finally, an interface system of digital to analog converters will be provided to
control the PAC IC. This will allow the logic sections of the radio to transmit
data over SPI and then activate the transmitter with a single digital line as
opposed to the present D/A output and saturation correction software.
Reference Oscillator
The reference oscillator will use a crystal at 26 MHz for MAGIC with a stability
over temperature of ± 20 ppm for GSM and ±11ppm for DCS 1800 to cover
the camping requiremments in Taichi. An SPI controlled AFC is provided for
by offsetting the fractional N division. Since an accurate clock is needed for
the logic sections of the radio, a secondary fractional N division system is
provided to derive an accurate low frequency clock. This low frequency clock