APN1005 SKYWORKS

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Skyworks Solutions, Inc. • Phone [781] 376-3000  Fax [781] 376-3100  sales@skyworksinc.com  www.skyworksinc.com 200314 Rev. A  Skyworks Proprietary Information  Products and Product Information are Subject to Change Without Notice.  July 21, 2005 1 APN1005: A Balanced Wideband VCO for Set-Top TV Tuner Applications APPLICATION NOTE Introduction Modern set-top TV DBS tuner systems require more channel coverage, while maintaining competitive prices. This situation creates tough design goals: to improve performance and simplify design. Balanced VCO configuration could be a competitive circuit solution, since it provides the widest tuning range with practical circuitry and layout. However, tuning margins would be further improved by optimizing the varactor manufacturing process. Skyworks has developed such a process to satisfy the most ambitious wideband design goals. In this publication, we will address the design of the balanced- type voltage control oscillator (VCO) based on the newly developed varactor SMV1265-011 with the unique set of capacitance tuning ratios and Q-quality. VCO Model Figure 1 shows the VCO model built for open loop analysis in Libra Series IV including the SMV1265-011 varactor model. The circuit schematic in Figure 2 shows a pair of transistors in a single feedback loop, connected so that collector currents would be 180° shifted (ideally). A pair of back-to-back connected SMV1265-011 varactors is used, rather than a single one. This allows lower capacitance at the high-voltage range, without changing the tuning ratio. The reason is that, apart from package capacitance, certain mounting fringing capacitances, though small, may strongly affect higher frequency margins. The effects of parasitic capacitances were summarized in the model as C and C3, valued 0.4 pF each. These values may vary depending on the layout of the board. Varactor DC biasing is provided through resistors R 6 and R8, both 1 k, which may affect the phase noise, but eliminate the need for inductive chokes. This minimizes overall costs and the possibility of parasitic resonances — the usual cause for frequency instability and spurs. The phase corrector DC chokes, SRL 1 and SRL2, were modeled as lossless inductors at 33 nH since their losses are dominated by the 30 Ω emitter biasing resistors. DC blocking series capaci- tances (C SER1 and CSER2) are modeled as an SRC network, including associated parasitics. Their values were optimized to 10 pF providing smooth tuning over the design band.

APPLICATION NOTE  APN1005 Skyworks Solutions, Inc.  Phone [781] 376-3000  Fax [781] 376-3100  sales@skyworksinc.com  www.skyworksinc.com 200314 Rev. A  Skyworks Proprietary Information  Products and Product Information are Subject to Change Without Notice.  July 21, 2005 3 The pseudo-resonator inductance is formed by microstrip trans- mission line TL2, which provides necessary circuit response at high frequencies. This has little effect at the lower band due to the resonator’s dominantly capacitive nature. The function of transmission line TL 1 is both feedback and phase alignment — providing flat power response over the tuning range. Power output is supplied from the collectors of X 1 or X2 through the series connected resistance and DC blocking capacitance SRC 2 and SRC3. DC biasing for both of the transistors is supplied through a resis- tive divider R1/R3/R2 . The NEC NE68119 bipolar transistors were selected to best fit performances. Note: The circuit is very sensitive to the transistor choice (in terms of tuning range and stability) due to wide band- width design requirements. For the model of NEC NE68119 we used the Gumel Poon model of Libra IV with the coefficients provided by CEL RF & Microwave Semiconductors Catalogue,1997-98. Figure 3. Libra Test Bench In the Libra test bench shown in Figure 3 we defined an open loop gain (Ku = VOUT/VIN) as the ratio of voltage phasors at the input and output ports of an OSCTEST component. Defining the oscillation point requires the balancing of input (loop) power to provide zero gain for a zero loop phase shift. Once the oscillation point is defined, the frequency and output power can be mea- sured. Use of the OSCTEST2 component for the close loop analysis is not recommended, since it may fail to converge in some cases, and doesn’t allow clear insight into the under- standing of VCO behavior. This property is considered an advantage of modeling over a purely experimental study. In the default bench shown in Figure 4 the variables used for more convenient tuning during performance analysis and opti- mization are listed in a “variables and equations” component.

and CP parameters as given in the Table 2. by the current subrange will still fit in the original curve. Table 1. Silicon Varactor Diode Default Values Table 2. Varactor Voltages

especially when analyzing the middle band area. demonstrates the model’s effectiveness. Table 3 shows the bill of materials used. Table 3. Bill of Materials

  1. Balanced Wideband VCO Simulation Project Files for Libra IV.
  2. Balanced Wideband VCO Circuit Schematic and PCB Layout for

Protel EDA Client, 1998 version.

  1. Balanced Wideband VCO Gerber Photo-plot Files
  2. Detailed measurement and simulation data.

© Skyworks Solutions, Inc., 1999. All rights reserved. of 0.84–2.23 GHz for the applied varactor voltage from 1–27 V. Table 4. Tabulated Measurement Data

APPLICATION NOTE  APN1005 Skyworks Solutions, Inc.  Phone [781] 376-3000  Fax [781] 376-3100  sales@skyworksinc.com  www.skyworksinc.com 200314 Rev. A  Skyworks Proprietary Information  Products and Product Information are Subject to Change Without Notice.  July 21, 2005 11 Copyright © 2002, 2003, 2004, 2005, Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Skyworks may change its documentation, products, services, specifications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes. No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided hereunder, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale. THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or environmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper use or sale. Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications or parameters. Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for identification purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.