STB4395 Datasheet, PDF (12/16 Pages) STMicroelectronics – CT2 RECEIVER/TRANSMITTER

STB4395
8 - TRANSCEIVER SECTION (continued)
8.3.3 - Channel Frequency Setting
8.3.3.1 - General Case
Using, from the divider ratios : and from the mixers :
FCH = CH*FX/288
FIF2= FRX - FIF1
FRX = RX *FX/16
F_IFTX = 0.5 *F_TX
F_TX = TX*F_SYN/18
FIF1= FRF - FCH
F_RF = F_CH+F_IFTX
the RF frequency is related to the other frequencies by :
F_RF = F_CH + F_IFTX
= CH * F_SYN/288 + TX * F_SYN/18 * 0.5
= FCH + FRX - FIF2 = CH * FSYN/288 + RX * FSYN/16 - FIF2
Hence the channel select input (15 of the 16 digits, see pin table, paragraph 1.4) serial data stream :
CH = (FRF - TX*FSYN/18*0.5 ) * 288/FSYN = 288* FRF /FSYN - 3008 and CH = 288 (FRF + FIF2)/FSYN - 3042
where :
F_CH is the channel PLL synthesizer frequency
F_IF1 is the first if frequency (receive)
FIF2 is the second if frequency (receive)
F_IFTX is the transmit if frequency
FRF is the desired rf frequency
FRX is the receive offset PLL frequency
FSYN is the reference input frequency (on SYNCLK)
F_TX is the transmit offset PLL frequency
RX is the fixed receive divide ratio of 169
TX is the fixed transmit divide ratio of 376
CH is the channel synthesizer divide ratio defined by the binary channel number,
e.g. D14,D13,...........D0
The channel synthesizer provides integral division for all numbers between 3968 and 32764 (binary
000111110000000 to 111111111111100).Binary numbers outside this range will cause division ratios not
directly related to binary code.
8.3.3.2 - Particular Case. with F_SYN = 14.4MHz :
F_RX = 152.1MHz
FTX = 300.8MHz
F_IFTX = 150.4MHz
FIF1 = 150.4MHz
FIF2 = 1.7MHz
Then CH = 20 * F_RF - 3008
Example : desired RF frequency, F_RF = 866.05MHz
Then substituting in : CH = 20*866.05-3008 = 14313 (binary 011011111101001)
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