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TDA7326 Datasheet(PDF) 6 Page - STMicroelectronics |
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TDA7326 Datasheet(HTML) 6 Page - STMicroelectronics |
6 / 16 page 3.3 DIVIDER FROM VCO FREQUENCY TO REFERENCE FREQUENCY This divider provides a low frequency fSYN which is phase compared with the reference frequency fREF. 3.4 OPERATING MODE Four operating modes are available: - FM mode, - AM swallow mode, - AM direct mode, - Standby mode They are user programmable with the SWR/DIR and AM/FM bits in the byte 2. Standby mode: all functions are stopped. This al- lows low current consumption without lost of infor- mation in all register, it is activated by forcing bit 0 (AM/FM) and bit 1 (SWM/DIR) both at zero value. 3.4.1 FM and AM (SW) Operation (Swallow Mode) The FM or AM signal is applied to a four modulus: 32/33/64/65 high speed prescaler, which is controlled by a 6 bit divider ’A’.This divider is controlled by the 6 bit SC register. In parallel the output of the prescaler is con- nected to a 8 bit divider ’B’. This divider is controlled by the 8 bit PC register. For FM mode with 25kHz reference frequency opera- tion, the divider A is a 5 bit divider. The high speed prescaler is working in : 32/33 dividing mode. Bit 6 of the SC register has to be kept to ”0”. Dividing range calculation : For FM mode with 12.5kHz reference fre- quency and SW swallow mode operation : fVCO =[ 65 ⋅ A1 +(B1 +1 - A1) ⋅ 64 ] . fREF or Important : For correct operation B ≥ 64 and B ≥ A. At FM mode with 25kHz reference frequency : fVCO =[ 33 ⋅ A2 +(B2 +1 - A2) ⋅ 32 ] ⋅ fREF Important: For correct operation B ≥ 32 and B ≥ A. A and B are variable values of the dividers. To keep the actual tuning frequency after a modification of the reference frequency, the values of the dividers have to be modified in the following way. Switching from 25kHz to 12.5kHz reference frequency : B1 =B2,A1 =A2 ⋅ 2 Switching from 12.5kHz to 25kHz reference frequency: B2 =B1,A2 = A1 2 and A2 = (A1 + 1) 2 for odd values A1. The AM signal is directly applied to the 14 bit static divider ’C’. This divider is controlled by both SC and PC registers. Dividing range: PREDIVIDER R OSC IN REGISTER SC5 .. SC0 COUNTER A PREDIVIDER M/M+1 AM IN FM IN REGISTER PC7 .. PC0 COUNTER B PD fref fsyn D94AU101 Figure 2: FM and AM (SW) operation (swallow mode) MODE SECTION SWM/DIR AM/FM STAND-BY 0 0 FM 1 0 AM SWALLOW 0 1 AM DIRECT 1 1 fVCO = (64 ⋅ B1 +A1 + 64) ⋅ fREF fVCO = (32 ⋅ B2 +A2 + 32) ⋅ fREF fVCO =(C + 1) ⋅ fREF TDA7326 6/16 |
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