A pp li c at i on N ot e , R ev . 2. 0 , N ov . 2 00 6 A p p li c a t i o n N o t e N o . 0 6 1 W - C D M A 2 . 3 G H z V C O u s i n g B F R 3 60 F an d B B Y 58 - 0 2 V R F & P r o t e c ti o n D e v i c e s Edition 2006-11-07 Published by Infineon Technologies AG 81726 München, Germany © Infineon Technologies AG 2009. All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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Life support devices or systems are intended to be implanted in the human body, or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. Application Note No. 061 Application Note No. 061 Revision History: 2006-11-07, Rev. 2.0 Previous Version: 2001-05-17 Page Subjects (major changes since last revision) All Document layout change Application Note 3 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V 1 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V Features • • • Low phase noise of < -90 dBc / Hz at 10 kHz using a low Q resonator 0 dBm output power at low current consumption Highly linear oscillation frequency versus control voltage curve 2 3 1 Package: TSFP-3 2 1 Package: SC79 1.1 Introduction 1.1.1 BFR360 The BFR360F is a silicon bipolar transistor housed in a small outline TSFP-3 package. A member of Infineon’s new 3+ generation transistor family, the BFR360F is a 14 GHz transition-frequency device which takes advantage of the latest manufacturing techniques requiring fewer processing steps than other devices in its class, thereby offering excellent performance and device-to device consistency at extraordinarily low cost. With a noise figure of 0.95 dB at 2 V / 5 mA, this device is a good solution for cost-sensitive LNA designs. In addition, the BFR360F is an ideal choice for VCO applications due to its low flicker noise (1/f noise) corner frequency of 15 kHz. 1.1.2 BBY58-02V The BBY58-02V is a hyper abrupt silicon varactor diode designed for low tuning voltage operation in VCOs employed in mobile communications equipment. If offers excellent linearity accompanied by a high quality factor and low series inductance. Other features are a high capacitance ratio and very low capacitance spread. The BBY58-02V is housed in a small outline SC79 package. Application Note 4 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V 1.1.3 Application Circuit Table 1 Typical Parameters of the Application Circuit Parameter Value VCC ICC fosc Vctrl Pout 3V Phase Noise <-90 dBc/Hz @ 10 kHz Sensitivity 49 MHz / V 8.5 mA 2300 MHz - 2360 MHz 0.85 V - 2 V 0 dBm A N061_Schematic.vsd Figure 1 Schematic Diagram Application Note 5 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V Table 2 Bill of Materials Name Value Package Manufacturer Function C1 330 pF 0402 Various RF Decoupling C2 3 pF 0402 Various RF Decoupling C3 0.6 pF 0402 AVX ACCU-P Tank Circuit C4 0.6 pF 0402 AVX ACCU-P Tank Circuit, DC Block C5 0.7 pF 0402 AVX ACCU-P Feedback C6 0.7 pF 0402 AVX ACCU-P Feedback C7 330 pF 0402 Various RF Ground C8 1.5 pF 0402 Various RF Ground C9 1.8 pF 0402 Various DC Block D1 BBY58-02V SC79 Infineon Varactor Diode, Tank Circuit L1 82 nH 0402 Toko LL1005-FH RF Choke L2 1.5 nH 0402 Toko LL1005-FH Tank Circuit L3 82 nH 0402 Toko LL1005-FH RF Choke L4 82 nH 0402 Toko LL1005-FH RF Choke Q1 BFR360F TSFP-3 Infineon Si BJT R1 22 kΩ 0402 Various Biasing R2 51 Ω 0402 Various Biasing 35 µm Cu 0.5 mm FR4 35 µm Cu for mechanical rigidity of PCB 0.5 mm FR4 35 µm Cu AN061_PCB_Cross_Section.vsd Figure 2 PC Cross Section Application Note 6 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V 1.2 Overview This application note describes the design of a voltage controlled oscillator. Tank Circuit BBY58-02V Generator BFR360F Out ΓG ΓT AN061_VCO_BlD.vsd Figure 3 VCO Block diagram Traditionally, all oscillators are classified as either a negative resistance oscillator (a.k.a. reflection oscillator) or a feedback oscillator. The criterion is whether there is an “obvious” feedback circuit. At RF and microwave frequencies, it becomes difficult to construct a feedback circuit without introducing excess phase shift. Therefore almost all oscillators in this frequency range are classified as a negative resistance oscillator. Figure 3 shows a block diagram of a negative resistance oscillator. In the negative resistance model, oscillators are represented as a combination of an active element (generator) and a passive element (tank circuit). The active element generates negative resistance and drives the passive element, which is usually a resonator. When the negative resistance is of sufficient magnitude to overcome all losses in the resonator and associated circuitry, an oscillation starts and builds up, rapidly achieving a steady-state condition. The oscillator design discussed in this application note is in Clapp configuration (Figure 4). The BFR360F is employed in the generator circuit to provide negative resistance. The BBY58-02V diode serves as a voltage controlled capacitor in the tank circuit to enable tuning of the oscillation frequency. The phase noise of an oscillator depends strongly o the 1/f noise performance of the transistor used, and even more so on the loaded Q-factor of the tank circuit. The Q-factor of the inductor element used in the tank circuit is especially critical. If the BFR360F transistor and the BBY58-02V tuning diode are used in an oscillator circuit, it is possible to achieve good phase noise performance, even with a low Q inductor. The oscillator design in this application note uses s standard 0402 chip inductor as the tank circuit inductive element. The chip coil used has a modest unloaded Q approximately 70 at 2.3 GHz. Despite this limitation, the oscillator’s phase noise is still better than -90 dBc / Hz at 10 kHz offset, with oscillator output power being a respectable 0 dBm / 1 mW Application Note 7 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V AN061_Clapp_Oscillator.vsd Figure 4 Clapp Oscillator 1.3 Circuit Topology Table 1 shows the topology that is used for this VCO design. Q1, the Infineon BFR360F transistor, is used in a common collector configuration and utilizes the feedback voltage divider C1 - C5 to provide appropriate phase-shift and feedback to enable oscillation to occur. The impedance that will be seen by the resonator on Q1’s base will be negative and the system is classified as a reflection oscillator. The system’s thermal noise will create a signal build-up between the generator and the resonating tank circuit that will build to an oscillation at a frequency determined by the resonator. L4 is chosen as an RF choke to provide a high impedance in the emitter circuit and to ensure that most of the oscillator power is fed back to the base of Q1 instead of being dissipated in R2. R2 is used for current feedback, providing a stable DC operating point that is less dependent on variations in transistor hFE. C7 and C8 serve as RF bypass capacitors and provide an RF ground at the BFR360F’s collector AN061_Layout_VCO.vsd Figure 5 Layout of the VCO The tank circuit is comprised of C3, C4, L2 and D1, the varactor diode BBY58-02V. These elements determine the VCO’s frequency of oscillation. It is lightly coupled to the BFR360F’s base through C4, the light coupling serving to maximize the loaded Q of the resonator. L1 is used as an RF choke, while C1 and C2 serve as RF bypass capacitors. C9 is the coupling capacitor that taps some of the energy out of the VCO. The less energy drained out of the oscillator circuit, the higher the loaded Q factor will be, and therefore the better the phase noise performance. However, the drawback is a low output power from the complete circuit. The loaded Q of the tank circuit can be augmented by increasing C6 or reducing C4. However, doing so reduces the loop gain in the oscillator, and sufficient loop gain has to be maintained to guarantee oscillation start-up under all conditions of temperature, supply voltage, ect. C4 determines the amount of coupling between the active device Application Note 8 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V and the resonator. The lighter the coupling (a lower value of C4 yields lighter coupling), the better the loaded Q of the resonator, which results in better phase noise performance. The trade-off is reduced VCO output power and as the coupling becomes lighter and lighter, the likelihood of the VCO to fail to achieve start-up increases. For this reason it is prudent to test the VCO for start-up at the maximum anticipated operating temperature and lowest specified operation voltage, to ensure sufficient gain margin to guarantee oscillator start-up under adverse conditions. 1.4 Measurement Results Figure 6 Measured Phase Noise Application Note 9 Rev. 2.0, 2006-11-07 Application Note No. 061 W-CDMA 2.3 GHz VCO using BFR360F and BBY58-02V AN061_Frequency(Vt).vsd Figure 7 Measure Frequency of Oscillation vs. Tune Voltage AN061_Pout(Vt).vsd Figure 8 Measured Output Power vs. Tune Voltage Table 3 Test Results Parameter Units Measured Performance Supply Voltage V 3 Supply Current mA 8.5 Control Voltage Range V 0.85 - 2 Operating Frequency Range MHz 2300 - 2360 Control Voltage Sensitivity MHz / V 49 Output Power into 50 Ω dBm 0 Phase Noise at 10 kHz dBc / Hz -90 Phase Noise at kHz dBc / Hz -113 Frequency Pushing (VCC = 3 V ± 0.25 V) kHz ±450 Harmonics dBc -13 Application Note 10 Rev. 2.0, 2006-11-07 Application Note No. 061 Summary and Remarks 2 Summary and Remarks Infineon’s newly introduced 3+ generation BFR360F bipolar transistor and BBY5x-02V varactor diodes offer a high performance, compact and low-cost solution for voltage controlled oscillator (VCO) designs. This application note describes a VCO design for WCDMA applications. The circuit offers a low phase noise of less than -90 dBc/Hz @ 10 kHz despite the fact that a standard, low-cost, low Q chip inductor is used in the resonator circuit. Of course one can not expect this VCO design to have tightly toleranced, highly repeatable frequency of oscillation since the tolerance of the inductor used in the tank circuit are ±0.3 nH, which corresponds to ±20 % of the nominal 1.5 nH value. The main purpose of this application note was not to present an oscillator suitable for mass production but to point out the excellent potential of the BFR360F transistor for low-cost, low phase noise VCOs. Evaluation boards for the VCO application described in this application note are available form Infineon Technologies. Application Note 11 Rev. 2.0, 2006-11-07