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ADF4110 Scheda tecnica(PDF) 9 Page - Analog Devices |
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ADF4110 Scheda tecnica(HTML) 9 Page - Analog Devices |
9 / 24 page Data Sheet ADF4153 Rev. F | Page 9 of 24 CIRCUIT DESCRIPTION REFERENCE INPUT SECTION The reference input stage is shown in Figure 11. SW1 and SW2 are normally closed switches. SW3 is normally open. When power-down is initiated, SW3 is closed and SW1 and SW2 are opened. This ensures that there is no loading of the REFIN pin on power-down. BUFFER TO R COUNTER REFIN 100k Ω NC SW2 SW3 NO NC SW1 POWER-DOWN CONTROL Figure 11. Reference Input Stage RF INPUT STAGE The RF input stage is shown in Figure 12. It is followed by a 2-stage limiting amplifier to generate the current-mode logic (CML) clock levels needed for the prescaler. BIAS GENERATOR 1.6V AGND AVDD 2kΩ 2kΩ RFINB RFINA Figure 12. RF Input Stage RF INT DIVIDER The RF INT CMOS counter allows a division ratio in the PLL feedback counter. Division ratios from 31 to 511 are allowed. INT, FRAC, MOD, AND R RELATIONSHIP The INT, FRAC, and MOD values, in conjunction with the R counter, make it possible to generate output frequencies that are spaced by fractions of the phase frequency detector (PFD). See the RF Synthesizer: A Worked Example section for more information. The RF VCO frequency (RFOUT) equation is RFOUT = FPFD × (INT + (FRAC/MOD)) (1) where: RFOUT is the output frequency of the external voltage controlled oscillator (VCO). INT is the preset divide ratio of the binary 9-bit counter (31 to 511). MOD is the preset fractional modulus (2 to 4095). FRAC is the numerator of the fractional division (0 to MOD − 1). The PFD frequency is given by: FPFD = REFIN × (1 + D)/R (2) where: REFIN is the reference input frequency. D is the REFIN doubler bit. R is the preset divide ratio of the binary 4-bit programmable reference counter (1 to 15). RF R COUNTER The 4-bit RF R counter allows the input reference frequency (REFIN) to be divided down to produce the reference clock to the PFD. Division ratios from 1 to 15 are allowed. THIRD-ORDER FRACTIONAL INTERPOLATOR FRAC VALUE MOD REG INT REG RF N DIVIDER N = INT + FRAC/MOD FROM RF INPUT STAGE TO PFD N-COUNTER Figure 13. RF N Divider |
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