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ML13175 Fiches technique(PDF) 6 Page - LANSDALE Semiconductor Inc. |
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ML13175 Fiches technique(HTML) 6 Page - LANSDALE Semiconductor Inc. |
6 / 16 page Figure 9. Change in Oscillator Frequency versus Oscillator Control Current Figure 10. Change in Oscillator Frequency versus Oscillator Control Current –100 ICont, OSCILLATOR CONTROL CURRENT (µA) 0 100 300 600 200 400 500 –100 0 100 300 600 200 400 500 ICont, OSCILLATOR CONTROL CURRENT (µA) VCC = 3.0 Vdc Imod = 2.0 mA TA = 25 °C fosc (ICont @ 0) 320 MHz VCC = 3.0 Vdc Imod = 2.0 mA TA = 25 °C fosc (ICont @ 0) 450 MHz 20 10 0 –10 – 20 – 30 – 40 20 10 0 –10 – 20 – 30 – 40 ML13175/ML13176 LANSDALE Semiconductor, Inc. EVALUATION PC BOARD The evaluation PCB, shown in Figures 26 and 27, is very versatile and is intended to be used across the entire useful frequency range of this device. The center section of the board provides an area for attaching all SMT components to the component ground side of the PCB (see Figures 28 and 29). Additionally, the peripheral area sur- rounding the RF core provides pads to add supporting and interface circuitry as a particular application requires. This evaluation board will be discussed and referenced in this section. CURRENT CONTROLLED OSCILLATOR (Pins 1 to 4) It is critical to keep the interconnect leads from the CCO (Pins 1 and 4) to the external inductor symmetrical and equal in length. With a minimum inductor, the maximum free running frequency is greater than 1.0 GHz. Since this inductor will be small, it may be either a microstrip inductor, an air wound inductor or a tune- able RF coil. An air wound inductor may be tuned by spreading the windings, whereas tunable RF coils are tuned by adjusting the position of an aluminum core in a threaded coilform. As the aluminum core coupling to the windings is increased, the induc- tance is decreased. The temperature coefficient using an alu- minum core is better than a ferrite core. The UniCoil™ induc- tors made by Coilcraft may be obtained with aluminum cores (Part No. 51–129–169). GROUND (Pins 5, 10 and 15) GROUND RETURNS: It is best to take the grounds to a back- side ground plane via plated through holes or eyelets at the pins. The application PCB layout implements this technique. Note that the grounds are located at or less than 100 mils from the device pins. DECOUPLING: Decoupling each ground pin to VCC isolates each section of the device by reducing interaction between sec- tions and by localizing circulating currents. LOOP CHARACTERISTICS (Pins 6 and 7) Figure 11 is the component block diagram of the ML1317x PLL system where the loop characteristics are described by the gain constants. Access to individual components of this PLL system is limited, inasmuch as the loop is only pinned out at the phase detector output and the frequency control input for the CCO. However, this allows for characterization of the gain constants of these loop components. The gain constants Kp, Ko and Kn are well defined in the ML13175 and ML13176. PHASE DETECTOR (Pin 7) With the loop in lock, the difference frequency output of the phase detector is DC voltage that is a function of the phase dif- ference. The sinusoidal type detector used in the IC has the fol- lowing transfer characteristic: le = A Sin θe The gain factor of the phase detector, Kp (with the loop in lock) is specified as the ratio of DC output current, le to phase error, θe: Kp = le/θe (Amps/radians) Kp = A Sin θe/θe Sin θe ~ θe for θe ≤ 0.2 radians; thus Kp Figures 7 and 8 show that the detector DC current is approxi- mately 30 µA where the loop loses lock at θe = ±π/2 radians; therefore Kp is 30 µA/radians. CURRENT CONTROLLED OSCILLATOR, CCO (Pin 6) Figures 9 and 10 show the non–linear change in frequency of the oscillator over an extended range of control current for 320 and 450 MHz applications. Ko ranges from approximately 6.3x105 rad/sec/µA or 100 kHz/µA (Figure 9) to 8.8x105 rad/sec/µA or 140 kHz/µA (Figure 10) over a relatively linear response of control current (0 to 100 µA). The oscillator gain factor depends on the operating range of the control current (i.e., the slope is not constant). Included in the CCO gain factor is the internal amplifier which can sink and source at least 30µA of input current from the phase detector. The internal cir- cuitry at Pin 6 limits the CCO control current to 50 µA of source capability while its sink capability exceeds 200 µA as shown in Figures 9 and 10. Further information to follow shows how to use the full capabilities of the CCO by addition of an external loop amplifier and filter (see Figure 15). This addition- al circuitry yields at Ko = 0.145 MHz/µA or 9.1x105 rad/sec/µA. Legacy Applications Information APPLICATIONS INFORMATION www.lansdale.com Page 6 of 16 Issue c = A (Amps/radians) |
Numéro de pièce similaire - ML13175 |
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Description similaire - ML13175 |
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