Circuit Note CN-0134 Devices Connected/Referenced Circuits from the Lab™ tested circuit designs address common design challenges and are engineered for quick and easy system integration. For more information and/or support, visit www.analog.com/CN0134. ADF4350 Fractional-N PLL IC with Integrated VCO ADL5375 Wideband Transmit Modulator ADP150 Low Noise 3.3 V LDO ADP3334 Low Noise Adjustable LDO Broadband Low Error Vector Magnitude (EVM) Direct Conversion Transmitter EVALUATION AND DESIGN SUPPORT CIRCUIT FUNCTION AND BENEFITS Circuit Evaluation Boards CN-0134 Evaluation Board (CFTL-CN0134-EVALZ) Design and Integration Files Schematics, Layout Files, Bill of Materials This circuit is a complete implementation of the analog portion of a broadband direct conversion transmitter (analog baseband in, RF out). RF frequencies from 500 MHz to 4.4 GHz are supported through the use of a PLL with a broadband integrated voltage controlled oscillator (VCO). Harmonic filtering of the LO from the PLL ensures excellent quadrature accuracy. ADP150 1µF 5.5V 1µF ADP3334 1µF 3.3V VVCO 16 17 VVCO FREF IN 28 10 DVDD AVDD 1µF 5.0V VDD I/Q SMA INPUTS 26 4 6 32 CE PDB RF VP SDV DD 1nF 1nF 29 REF IN 51Ω VPS1, VPS2 RFOUTB+ 14 2 DATA SPI-COMPATIBLE SERIAL BUS VVCO IBBN RFOUTB– 15 1 CLK ZBIAS 3 LE ADF4350 ZBIAS LOIP RFOUTA+ 12 22 RSET LOIN RFOUTA– 13 4.7kΩ VTUNE 20 CPOUT CPGND SDGND AGND AGNDVCO 31 9 11 18 21 180Ω 7 SW 5 8 ADL5375 IBBP 22nF DGND 330nF QUADRATURE PHASE SPLITTER RFOUT QBBP 10nF QBBN 82Ω 27 I/Q SMA INPUTS 08659-001 5.5V Figure 1. Direct Conversion Transmitter (Simplified Schematic: All Connections and Decoupling Not Shown) Rev. B Circuits from the Lab™ circuits from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com/circuits Fax: 781.461.3113 ©2010 Analog Devices, Inc. All rights reserved. Circuit Note 08659-002 CN-0134 Figure 2. Evaluation Board for CN-0134 Direct Conversion Transmitter Low noise LDOs ensure that the power management scheme has no adverse impact on phase noise and EVM. This combination of components represents industry-leading direct conversion transmitter performance over a frequency range of 500 MHz to 4.4 GHz CIRCUIT DESCRIPTION The circuit shown in Figure 1 utilizes the ADF4350, a fully integrated fractional-N PLL IC, and the ADL5375 wideband transmit modulator. The ADF4350 provides the local oscillator (LO) signal for the ADL5375 transmit quadrature modulator, which upconverts analog I/Q signals to RF. Taken together, the two devices provide a wideband baseband IQ to RF transmit solution. The ADF4350 is powered off the ultralow noise 3.3 V ADP150 regulator for optimal LO phase noise performance. The ADL5375 is powered off a 5 V ADP3334 LDO. The ADP150 LDO has an output voltage noise of only 9 µV rms and helps to optimize VCO phase noise and reduce the impact of VCO pushing (equivalent to power supply rejection). Filtering is required on the ADF4350 RF outputs to attenuate harmonic levels so as to minimize errors in the quadrature generation block of the ADL5375. From measurement and simulation, the odd order harmonics contribute more than even order harmonics to quadrature error and, if attenuated to below −30 dBc, results in sideband suppression performance of −40 dBc or better. The ADF4350’s 2nd harmonic (2H) and 3rd harmonic (3H) levels are as given in the data sheet and shown in Table 1. To get the 3rd harmonic below -30 dBc, approximately 20 dB of attenuation is required. Table 1. ADF4350 RF Output Harmonic Levels Unfiltered Harmonic Content (Second) Harmonic Content (Third) Harmonic Content (Second) Harmonic Content (Third) −13 dBc Fundamental VCO output Fundamental VCO output −20 dBc Divided VCO output −10 dBc Divided VCO output −19 dBc This circuit gives four different filter options to cover four different bands. The filters were designed for a 100 Ω differential input (ADF4350 RF outputs with appropriate matching) and 50 Ω differential output (ADL5375 LOIN differential impedance). A Chebyshev response was used for optimal filter roll-off at the expense of increased pass-band ripple. The filter schematic is shown in Figure 3. This topology allows the use of either a fully differential filter to minimize component count, a single-ended filter for each output, or a combination of the two. It was determined that for higher frequencies (>2 GHz) two single-ended filters gave the best performance because the series inductor values are twice the value compared to a fully differential filter and, hence, the impact of component parasitics is reduced. For lower frequencies (<2 GHz), a fully differential filter provides adequate results. Rev. B | Page 2 of 5 Circuit Note CN-0134 Table 2. ADF4350 RF Output Filter Component Values (DNI = Do Not Insert) Frequency Range (MHz) ZBIAS L1 (nH) L2 (nH) C1a (pF) C1c (pF) C2a (pF) C2c (pF) C3a (pF) C3c (pF) a. 500–1300 27 nH|| 50 Ω 3.9 3.9 DNI 4.7 DNI 5.6 DNI 3.3 b. 850–2450 19 nH || (100 Ω in position C1c) 2.7 2.7 3.3 100 Ω 4.7 DNI 3.3 DNI c. 1250–2800 50 Ω 0Ω 3.6 DNI DNI 2.2 DNI 1.5 DNI d. 2800–4400 3.9 nH 0Ω 0Ω DNI DNI DNI DNI DNI DNI 0 NO FILTERING FILTER B: 850MHz TO 2450MHz –10 –20 SSB (dBc) The filter should be designed with a cutoff approximately 1.2 to 1.5 times the highest frequency in the band of interest. This allows margin in the design, as typically the cutoff will be lower than designed due to parasitics. The effect of PCB parasitics can be simulated in an EM simulation tool for improved accuracy. –30 –40 –50 –60 –70 800 1000 1200 1400 1600 1800 2000 2200 2400 FREQUENCY (MHz) 08659-004 The ADF4350 output match consists of the ZBIAS pull-up and, to a lesser extent, the decoupling capacitors on the supply node. To get a broadband match it is recommended to use either a resistive load (ZBIAS = 50 Ω) or a resistive in parallel with a reactive load for ZBIAS. The latter gives slightly higher output power, depending on the inductor chosen. Note that it is possible to place the parallel resistor as a differential component (i.e. 100 Ω) in position C1c to minimize board space. This is done in filter type c, described in Table 2. Figure 4. Sideband Suppression for Filter b, 850 MHz to 2450 MHz 3.3V ZBIAS L1 RFOUTA+ 13 ZBIAS RFOUTA– 12 ADF4350 C1a C1c L1 C1a MAGNITUDE ERROR (I/Q ERROR PHASE) C2a L2 C2c L2 C2a C3a 1nF 9 LOIP 10 LOIN ERROR VECTOR MEASURED SIGNAL C3c 1nF C3a PHASE ERROR (I/Q ERROR PHASE) ADL5375 0 IDEAL SIGNAL (REFERENCE) Figure 3. ADF4350 RF Output Filter Schematic I As can be seen from Table 2, at lower frequencies below 1250 MHz, a 5th order filter is required. For 1.25 GHz to 2.8 GHz, 3rd order filtering is sufficient. For frequencies above 2.8 GHz, no filtering is required, as the harmonic levels are sufficiently low to meet sideband suppression specifications. 08659-005 0.1µF Q 120pF 08659-003 120pF Figure 5. EVM Plot A sweep of sideband suppression vs. frequency is shown in Figure 4 for the circuit using Filter b (850 MHz to 2450 MHz). In this sweep, the test conditions were the following: baseband I/Q amplitude = 1 V p-p differential sine waves in quadrature with a 500 mV (ADL5375-05) dc bias; baseband I/Q frequency (fBB) = 1 MHz. Rev. B | Page 3 of 5 CN-0134 Circuit Note Table 3. Single-Carrier W-CDMA Composite EVM Results Comparing Filter vs. No Filter on ADF4350 RF Outputs (Measured As Per 3GPP Specification Test Model 4) Composite EVM No LO Filtering 3.50% 3.40% 3.30% Frequency (MHz) 2140 1800 900 Composite EVM with LO Filtering, Filter C 1.80% 1.50% 0.90% Error vector magnitude (EVM) is a measure of the quality of the performance of a digital transmitter or receiver and is a measure of the deviation of the actual constellation points from their ideal locations, due to both magnitude and phase errors. This is shown in Figure 5. EVM measurements are given in Table 3 comparing results with and without the filter. In this case the baseband I/Q signals were generated using 3GPP test model 4 using a Rhode and Schwarz AMIQ I/Q Modulation Generator with differential I and Q analog outputs. Filter b was also used. A block diagram of the test setup for EVM is given in Figure 6. In addition to the improvement in sideband suppression and EVM, there is also a performance benefit to driving the ADL5375 LO inputs differentially. This improves modulator OIP2 performance by 2 dB to 5 dB, compared with singleended LO drive. Note that most external VCOs only come with a single-ended output, so using the differential outputs on the ADF4350 provides a benefit over an external VCO in this case. Figure 7 shows sideband suppression results using an 850 MHz to 2450 MHz filter (filter b). 10 Adjacent channel leakage ratio (ACLR) is a measure of the power in adjacent channels relative to the main channel power and is specified in dBc. SSB #10 +5dBm SSB #10 +2dBm SSB #10 –1dBm SSB #10 –4dBm 0 –10 SSB (dBc) The LO phase noise and the linearity of the modulator are the main contributors to ACLR. The ACLR test setup is the same as for EVM with the exception that coaxial filters were placed on the I/Q outputs of the signal generator to reduce aliasing products. Modulator Output Power (dBm) −7 −7 −7 –20 –30 –40 –60 0 500 1000 1500 2000 2500 3000 3500 FREQUENCY (MHz) R&S AMIQ GEN. I+ I– Q+ Figure 7. Sideband Suppression Results for 850 MHz to 2450 MHz Filter b SPECTRUM ANALYZER [R&S FSQ 8] Q– CN-0134 EVALUATION BOARD 08659-004 –50 A complete design support package for this circuit note can be found at http://www.analog.com/CN0134-DesignSupport. RF OUT COMMON VARIATIONS POWER SUPPLY Figure 6. EVM Measurement Setup (Simplified Diagram) 08659-006 5.5V It is possible to use the auxiliary outputs on the ADF4350 to switch between two filter types where wideband operation beyond that possible with one single filter is required. This is shown in Figure 8. An RF double-pole, 4-throw switch (DP4T) is used to select the differential outputs of either Filter 1 or Filter 2. Rev. B | Page 4 of 5 Circuit Note CN-0134 1nF RFOUTA+ 13 FILTER 1 9 LOIP 10 LOIN 1nF RFOUTA– 12 for software installation and test setup. Also see the AD4350 and ADL5375 data sheets for additional details. LEARN MORE DP4T SWITCH CN0134 Design Support Package: http://www.analog.com/CN0134-DesignSupport RFOUTB+ 14 FILTER 2 ADF4350 ADL5375 08659-008 RFOUTB– 15 Figure 8. Application Diagram Showing Possibility of Filter Switching Using the ADF4350 Main and Auxiliary Outputs CIRCUIT EVALUATION AND TEST ADIsimPLL Design Tool ADIsimPower Design Tool ADIsimRF Design Tool AN-0996 Application Note. The Advantages of Using a Quadrature Digital Upconverter (QDUC) in Point-to-Point Microwave Transmit Systems. Analog Devices. The CFTL-0134-EVALZ evaluation board contains the circuit described in circuit note CN-0134, allowing for the quick setup and evaluation of the circuit’s performance. The control software for the CFTL-0134-EVALZ board uses the standard ADF4350 programming software, located on the CD that accompanies the evaluation board. AN-1039 Application Note. Correcting Imperfections in IQ Modulators to Improve RF Signal Fidelity. Analog Devices. Equipment Needed ADL5375 Data Sheet A standard PC running Windows® XP, Windows Vista (32-bit), or Windows 7 (32-bit) with USB port, the CFTL-0134-EVALZ circuit evaluation board, and the ADF4350 programming software, power supplies, I-Q signal source, such as a Rhode & Schwarz AMIQ, and a spectrum analyzer such as the Rhode & Schwartz FSQ8. For additional details see the evaluation guide (CN0134-EvalGuide-RevA.pdf), which is contained in the design support package (http://www.analog.com/CN0134DesignSupport), and the ADF4350 and ADL5375 data sheets. ADL5375 Evaluation Board Getting Started See CN0134-EvalGuide-RevA.pdf for software installation and test setup. The documentation also includes the block diagram, the application schematic, the bill of materials, and the layout and assembly information. Also see the AD4350 and ADL5375 data sheets for additional details. Functional Block Diagram See Figure 1 and Figure 6 in circuit note CN-0134 and the CN0134-EvalGuide-RevA.pdf, Wideband TX Modulator Solution user document in the design support package. Data Sheets and Evaluation Boards ADF4350 Data Sheet ADF4350 Evaluation Board ADP150 Data Sheet ADP3334 Data Sheet REVISION HISTORY 11/10—Rev. A to Rev. B Changes to Circuit Note Title .......................................................... 1 Added Evaluation and Design Support Section ............................ 1 Changes to Circuit Description Section......................................... 2 Changes to Figure 6 .......................................................................... 4 Added Circuit Evaluation and Test Section ................................... 5 9/10—Rev. 0 to Rev. A Changes to Circuit Note Title .......................................................... 1 Changes to Circuit Function and Benefits Section....................... 1 Changes to Circuit Description Section......................................... 2 Changes to Common Variations Section ....................................... 4 1/10—Revision 0: Initial Version Setup and Test See circuit note CN-0134 and the CN0134-EvalGuideRevA.pdf, Wideband TX Modulator Solution user document, (Continued from first page) Circuits from the Lab circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the Circuits from the Lab circuits. Information furnished by Analog Devices is believed to be accurate and reliable. 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