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ADF4219L Fiches technique(PDF) 9 Page - Analog Devices |
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ADF4219L Fiches technique(HTML) 9 Page - Analog Devices |
9 / 24 page REV. C ADF4217L/ADF4218L/ADF4219L –9– CIRCUIT DESCRIPTION Reference Input Section The reference input stage is shown in Figure 2. 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. POWER-DOWN CONTROL REFIN NC NC NO SW3 SW2 SW1 50k BUFFER TO R COUNTER NC = NORMALLY CLOSED NO = NORMALLY OPEN Figure 2. Reference Input Stage IF/RF Input Stage The IF/RF input stage is shown in Figure 3. It is followed by a two-stage limiting amplifier to generate the CML clock levels needed for the prescaler. 500 500 1.6V BIAS GENERATOR RFINA RFINB AVDD AGND Figure 3. IF/RF Input Stage Prescaler The dual modulus prescaler (P/P + 1), along with the A and B counters, enables the large division ratio, N, to be realized (N = BP + A). This prescaler, operating at CML levels, takes the clock from the IF/RF input stage and divides it down to a manageable frequency for the CMOS A and B counters. It is based on a synchronous 4/5 core. The prescaler is selectable. On the IF side, it can be set to either 8/9 (DB20 of the IF AB Counter Latch set to 0) or 16/17 (DB20 set to 1). On the RF side of the ADF4217L/ADF4218L, it can be set to 64/65 or 32/33. On the ADF4219L, the RF prescaler can be set to 16/17 or 32/33. See Tables V, VI, VIII, and IX. A AND B COUNTERS The A and B CMOS counters combine with the dual modulus prescaler to allow a wide ranging division ratio in the PLL feed- back counter. The devices are guaranteed to work when the prescaler output is 188 MHz or less. Typically they will work with 250 MHz output from the prescaler. TO PFD N = BP + A LOAD LOAD MODULUS CONTROL FROM IF/RF INPUT STAGE 11(13)-BIT B COUNTER 6(5)-BIT A COUNTER PRESCALER P/P+1 Figure 4. Reference Input Stage, A and B Counters VCP – V 6 0 –6 0 5.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 4 2 –2 –4 VP = 5V ICP = 4mA TPC 13. Charge Pump Output Characteristics |
Numéro de pièce similaire - ADF4219L_15 |
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Description similaire - ADF4219L_15 |
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