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ADF4007 Datasheet(PDF) 11 Page - Analog Devices |
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ADF4007 Datasheet(HTML) 11 Page - Analog Devices |
11 / 16 page ADF4007 Rev. 0 | Page 11 of 16 APPLICATIONS FIXED HIGH FREQUENCY LOCAL OSCILLATOR Figure 13 shows the ADF4007 being used with the HMC358MS8G VCO from Hittite Microwave Corporation to produce a fixed-frequency LO (local oscillator), which could be used in satellite or CATV applications. In this case, the desired LO is 6.7 GHz. The reference input signal is applied to the circuit at FREFIN and, in this case, is terminated in 50 Ω. Many systems would have either a TCXO or an OCXO driving the reference input without any 50 Ω termination. To bias the REFIN pin at AVDD/2, ac coupling is used. The value of the coupling capacitor used depends on the input frequency. The equivalent impedance at the input frequency should be less than 10 Ω. Given that the dc input impedance at the REFIN pin is 100 kΩ, less than 0.1% of the signal is lost. The charge pump output of the ADF4007 drives the loop filter. In calculating the loop filter component values, a number of items need to be considered. In this example, the loop filter was designed so that the overall phase margin for the system is 45°. Other PLL system specifications are as follows: KD = 5 mA KV = 100 MHz/V Loop Bandwidth = 300 kHz FPFD = 106 MHz N = 64 All these specifications are needed and used with the ADIsimPLL to derive the loop filter component values shown in Figure 13. The circuit in Figure 13 gives a typical phase noise performance of −100 dBc/Hz at 10 kHz offset from the carrier. Spurs are heavily attenuated by the loop filter and are below −90 dBc. The loop filter output drives the VCO, which, in turn, is fed back to the RF input of the PLL synthesizer and also drives the RF output terminal. A T-circuit configuration provides 50 Ω matching between the VCO output, the RF output, and the RFIN terminal of the synthesizer. ADF4007 N2 N1 M2 M1 100pF 100pF 100pF CP MUXOUT 5.6nF 51 Ω 18 Ω 22 Ω NOTE DECOUPLING CAPACITORS (0.1mF/10pF) ON AVDD, DVDD, AND VP OF THE ADF4007 AND ON VCC OF THE AD820 AND THE HMC358MS8G HAVE BEEN OMITTED FROM THE DIAGRAM TO AID CLARITY. RSET AVDD DVDD VP FREFIN VCO 100MHz/V HMC358MS8G RSET 5.1k Ω 6 17 18 8 20 15 19 9 3 2 10 RFINA RFINB 5 4 11 12 13 14 GND 47nF AVDD 7 DVDD 16 REFIN AVDD = 3.3V 1k Ω 18k Ω VCC = 12V VCC = 3.3V 1k Ω AD820 10pF 18 Ω 100pF 18 Ω 100pF RFOUT LOGIC HI LOGIC HI LOGIC LO LOGIC LO Figure 13. 6.78 GHz Local Oscillator Using the ADF4007 |
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Similar Description - ADF4007 |
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