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TDA7427A Datasheet(PDF) 8 Page - STMicroelectronics |
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TDA7427A Datasheet(HTML) 8 Page - STMicroelectronics |
8 / 21 page DIVIDER FROM VCO FREQUENCY TO REFERENCE FREQUENCY This divider provides a low frequency fSYN which phase is compared with the reference frequency fREF. It is controlled by the registers PC0 to PC4 and PC5 to PC15 OPERATING MODES Four operating modes are available fo PLL; they are user programmable with the Mode PM regis- ters (see table below). PM0 PM1 Operating Mode 0 0 Standby 1 0 AM (swallow) 0 1 AM (direct) 11 FM - Standby mode: in this mode all device func- tions are stopped. This allows low current consumption without loss of information in all registers. The pin LP-OUT is forced to 0V, and all data registers are set to EFH. The os- cillator keeps running. - FM and AM (SW) Swallow Mode (SW): in this mode the FM or AM signal is applied to a 32/33 prescaler, which is controlled by a 5 bit divider ’A’.The 5 bit register (PC0 to PC4) controls this divider. In parallel the output of the prescaler is connected to a 11 bit divider ’B’. (PC5 to PC15). fOSC = (R+1) ⋅ fREF Dividing range calculation : fVCO =[ 33 ⋅ A + (B + 1 - A) ⋅ 32 ] ⋅ fREF fVCO = (32 ⋅ B + A + 32) ⋅ fREF Important:for correct operationA ≤ 32,B ≥ A,with A andB variable values of the dividers). - AM direct mode: the AM signal is applied di- rectly to the 16 bit static divider ’C’. (PC0 to PC15) fOSC =(R + 1) ⋅ f REF Dividing range: fVCO =(C + 1) ⋅ fREF THREE STATE PHASE COMPARATOR The phase comparator generates a phase error signal according to phase difference between fSYN and fREF. This phase error signal drives the charge pump current generator (fig. 3) CHARGE PUMP CURRENT GENERATOR This stage generates signed pulses of current. The phase error signal decides the duration and polarity of those pulses. The current absolute values are programmable by A0, A1, A2 registers for high current and B0, B1, registers for low current. LOW NOISE CMOS OP-AMP An internal voltage divider at pin VREF connects the positive input of the low noise Op-Amp. The charge pump output connects the negative input. This internal amplifier in cooperation with external components can provide an active filter. OSC IN REGISTER RC0 ... RC15 PREDIVIDER :R PHASE DETECTOR AM IN FM IN REGISTER PC0 ... PC15 PRESCALER :C fref fsyn D95AU376A ∆ϕ TO CHARGE PUMP Figure 2. AM direct mode operation for SW, MW and LW TDA7427A 8/21 |
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