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Transcript
AN41 E XTE NDE D F REQUE NCY O PE RAT ION R A D I O F R E Q U E NC Y S YNTHESIZERS 1. Introduction The frequency range of selected Silicon Laboratories RF synthesizers may be extended using a short in place of the external tuning inductor. Some applications require frequency ranges that cannot be accommodated by the standard Silicon Laboratories offerings. This application note details how to extend the upper frequency limits of the external-inductor synthesizers such as the Si4133. Only specific synthesizers may be used with an extended frequency range. The data sheets of applicable synthesizers will reference this application note. These data sheets will provide two frequency ranges: a center frequency range and an extended center frequency range. OF S I L I C O N L ABORATORIES tuning range must also be reserved to compensate for a ±10% inductor tolerance. When the external inductor is zeroed, however, variation in LEXT is negligible and more of this tuning range is available for the channel frequency range. Refer to the synthesizer’s data sheet for details. 3. Printed Circuit Board Layout The MLP is required for extended frequency range operation because it has a smaller package inductance. Figure 1 illustrates the recommended PCB pattern for LEXT = 0 nH. This figure illustrates shorts on the RF1, RF2, and IF oscillators. Refer to the data sheet for details about which oscillators may be operated with LEXT = 0 nH. 2. Oscillator Center Frequency and Inductor Choice The oscillator is tuned using a parallel capacitorinductor tank circuit. The capacitor is internal to the synthesizer and the inductor is formed by package and external inductances. The center frequency is determined by adjusting the inductance and is given by the following expression: 1 f CEN = --------------------------------------------------------------2 L PKG + L EXT C NOM The application designer selects the frequency operating range by selecting LEXT. LPKG and CNOM are fixed by the design of the synthesizer and packaging. The smallest LC product maximizes the output frequency. Zero LEXT minimizes the LC product. Figure 1. Example PCB MLP Layout with RF1, RF2, and IF External-Inductor Tuning Pins Set to 0 nH. Internal-inductor synthesizers, such as the Si4136, utilize an internal bond wire inductor. All inductance is from LPKG, and the frequency range is fixed. This series of synthesizers is typically centered between 2 GHz and 2.5 GHz. 4. Operating Condition Requirements External-inductor synthesizers, such as the Si4133, are designed to be tuned by an external inductor. When LEXT = 0 nH, the oscillator will oscillate at a higher frequency tuned by LPKG, approximately 1.8 GHz to 2 GHz. Extended frequency operation requires a higher bias voltage for certain analog stages within the synthesizer. The following steps implement this change: Silicon Laboratories specifies an allowable channel frequency range of ±5% for the external-inductor synthesizers. This range is limited because some of the Rev. 0.1 10/06 Some changes are required in the operating specifications to support extended frequency operation. 1. Set VDDR, VDDI, and VDDD to between 3.0 V and 3.6 V. 2. Set bit D1 of the Main Configuration Register (see Copyright © 2006 by Silicon Laboratories AN40 AN41 Table 1) to 1. Table 1. Main Configuration Register Bit D17 D5 D4 D3 D2 D1 D0 LPWR 0 AUTOPDB AUTOKP 1 0 ... Name 0 Key synthesizer specifications, such as phase noise and output power, may also change with extended frequency operation. Refer to the synthesizer’s data sheet for more detail. 5. Conclusion The output frequency range can be extended for selected Silicon Laboratories synthesizers by performing the following steps: 1. Review the revised specifications for Extended Frequency Operation in the synthesizer’s data sheet. 2. Design the PCB for a short under the RFLA-RFLB or RFLC-RFLD tuning pins of a designated MLP synthesizer. 3. Ensure that a minimum 3.0 V supply voltage is furnished to the synthesizer. 4. Set bit D1 of Main Configuration Register to 1. 2 Rev. 0.1 AN41 NOTES: Rev. 0.1 3 Simplicity Studio One-click access to MCU tools, documentation, software, source code libraries & more. Available for Windows, Mac and Linux! www.silabs.com/simplicity MCU Portfolio www.silabs.com/mcu SW/HW www.silabs.com/simplicity Quality www.silabs.com/quality Support and Community community.silabs.com Disclaimer Silicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementers using or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specific device, and "Typical" parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. Silicon Laboratories reserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracy or completeness of the included information. Silicon Laboratories shall have no liability for the consequences of use of the information supplied herein. This document does not imply or express copyright licenses granted hereunder to design or fabricate any integrated circuits. The products must not be used within any Life Support System without the specific written consent of Silicon Laboratories. A "Life Support System" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expected to result in significant personal injury or death. Silicon Laboratories products are generally not intended for military applications. Silicon Laboratories products shall under no circumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons. 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