EZZE SL900A, Technical Manual, Page: 68 / 116

M
ODEL
SL900A V
ERSION
V_1.0
P
REPARED BY
H/W D
ATE
2006.06.30
S
UBJECT
T
ECHNICAL
M
ANUAL
P
AGE
48/51
SL900A T
ECHNICAL
M
ANUAL
3. TX VCO
Two power VCOs are integrated with OPLL to form a complete transmitter circuit. The TX VCO
output power is typically 9dBm with +/-2.5dB variation in EGSM bands and +8dBm output power
with +/-2dB variation in DCS1800/PCS1900 bands over extreme Temperature conditions.
The PAM(RF3146) Input range is Typically 3dBm. So 5dB Attenuator is added Between MT6129 and
RF3146. Tx VCO Trequency Range is same with Trasnsceiver Frequency Range.
4. Frequency Synthesizer
The MT6120 includes a frequency synthesizer with a fully integrated RF VCO to generate RX and TX
local oscillator frequencies. The PLL locks the RF VCO to a precision reference frequency at 26MHz.
To reduce the acquisition time or to enable fast settling time for multi-slot data services such as GPRS,
a digital loop along with a fast-acquisition system are implemented in the synthesizer. After the
calibration, a fast-acquisition system is utilized for a period of time to facilitate fast locking.
The frequency ranges of the synthesizer for RX mode are
RX mode GSM850 1737Mhz ~ 1788Mhz
E-GSM900 1850Mhz ~ 1920Mhz
DCS1800 1805Mhz ~ 1880Mhz
PCS1900 1930Mhz ~1990Mhz
The Calculate LO Freqnecy Fvco from RX Channel Frequency Fch is following.
Fvco = 2*Fch-200K for GSM850 and E-GSM900
Fvco = Fch-100K for DCS1800 and PCS1900.
The frequency ranges of the synthesizer for TX mode are
TX mode GSM850 1813Mhz ~ 1868Mhz
E-GSM900 1936Mhz ~ 2059Mhz
DCS1800 1881Mhz ~ 2008Mhz
PCS1900 2035Mhz ~2149Mhz
The Calculate LO Freqnecy Fvco from TX Channel Frequency Fch is following.
(set the divider ratio D1 of TX reference divider = 11)
Fvco = 2*D1*Fch/(D1-1) for GSM850 and E-GSM900
Fvco = D1*Fch/(D1-1) for DCS1800 and PCS1900.
The MT6129 uses a digital calibration technique to reduce the PLL settling time Once the RF
synthesizer is programmed through a 3-wire serial interface, the calibration loop is activated. The main
function of the calibration loop is to preset the RF VCO to the vicinity of the desired frequency
quickly and correctly, thus aiding the PLL to settle faster. On the other hand, since a large portion of