STB4395 datasheet(12/16 Pages) STMICROELECTRONICS

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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

FIF1=FRF -FCH

FIFTX = 0.5 *FTX

FRF =FCH+FIFTX

FTX = TX*FSYN/18

the RF frequency is related to the other frequencies by :

FRF =FCH +FIFTX

=CH * FSYN/288 + TX * FSYN/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 :

FCH is the channel PLL synthesizer frequency

FIF1 is the first if frequency (receive)

FIF2 is the second if frequency (receive)

FIFTX 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)

FTX 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 FSYN = 14.4MHz :

FRX = 152.1MHz

FTX = 300.8MHz

FIFTX = 150.4MHz

FIF1 = 150.4MHz

FIF2 = 1.7MHz

Then CH = 20 * FRF - 3008

Example : desired RF frequency, FRF = 866.05MHz

Then substituting in : CH = 20*866.05-3008 = 14313 (binary 011011111101001)

STB4395

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