Rf Gsm Transmitter; Blue Module (Algae) - Motorola V975 Service Manual

Theory of Operation

RF GSM Transmitter

RF GSM Transmitter
BLUE MODULE IC (PRIMSYN GSM_TX)
The PRIMSYN receives SSI TX data at DMCS (digi-
tal input to start Tx modulation), TXCLK (clock for
serial transfer) and SDTX (serial Tx data) from POG.
This data pattern input to a fractional N synthesizer with
a 24-bit resolution. For EGSM the synthesizer output
is 880 – 915MHz, DCS is 1710 – 1785MHz with
GMSK modulation and is directly amplified to the trans-
mitter output.
Figure 3-7. PRIMSYN (GSM TX)
DP
SYNTH_FDBK
LP
TX_TUNE
FILTER
LP
RX_TUNE
FILTER
3-6
BDX
TX
GMSK BCLKX
DAC
SSI
DMCS
FracN
Y500
PLL
PRIMSYN
(U900)
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BLUE MODULE (ALGAE)

TRANSMIT SECTION
An integrated VCO is used for the transmit path. A single
VCO is used for transmit. A low noise floor divide-by-
2 stage drives the high band output. The low band out-
put is driven by a divide-by-4 stage.
Figure 3-8. ALGAE MB (Transceiver)
RX VCO
TX_OUT_LO
/2
TX_OUT_HI
Two transmit output stages are provided. Both stages
have integrated output matches in order to reduce the
required number of discrete components. The integrated
matches are implemented as differential to single-ended
transformers.
The transmit signal is fed back to the synthesizer through
a differential output stage that is shared with the re-
ceiver.
V975/V980
ALGAE MB
(U900)
RX_TUNE
SYNTH_FDBK
TX VCO
/2 /2
TX_TUNE
/2
Draft 1.0