Circuit Note CN-0311 Devices Connected/Referenced Circuits from the Lab™ reference circuits are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0311. ADF4351 Fractional-N PLL IC with Integrated VCO ADL5385 Wideband Transmit Modulator ADP150 Low Noise 3.3 V LDO ADP3334 Low Noise Adjustable LDO Broadband, Low Error Vector Magnitude (EVM) Direct Conversion Transmitter Using LO Divide-by-2 Modulator EVALUATION AND DESIGN SUPPORT CIRCUIT FUNCTION AND BENEFITS Circuit Evaluation Boards ADF4351 Evaluation Board (EVAL-ADF4351EB1Z) ADL5385 Evaluation Board (ADL5385-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 30 MHz to 2.2 GHz are supported by using a phase-locked loop (PLL) with a broadband integrated voltage controlled oscillator (VCO). Unlike modulators that use a divide-by-1 local oscillator (LO) stage (as described in CN-0285), harmonic filtering of the LO is not required. ADP150 5.5V ADP3334 5.5V 1µF 1µF 1µF 1µF 3.3V 5.0V VVCO VDD 16 17 VVCO 28 26 4 10 DVDD AVDD I/Q SMA INPUTS 6 CE PDB RF VP 32 SDV DD VPS1, VPS2 1nF 1nF FREF IN RFOUTB+ 14 VVCO IBBN RFOUTB– 15 1 CLK 2 DATA ZBIAS ZBIAS 3 LE SPI-COMPATIBLE SERIAL BUS ADL5385 IBBP 29 REF IN 51Ω LOIP RFOUTA+ 12 ADF4351 1nF 22 RSET 4.7kΩ LOIN RFOUTA– 13 DIVIDE-BY-2 QUADRATURE PHASE SPLITTER RFOUT 1nF VTUNE 20 QBBP 180Ω CPOUT 7 QBBN 330nF 22nF SW 5 8 SDGND AGND 31 9 AGNDVCO 11 18 21 DGND 27 I/Q SMA INPUTS 11268-001 CPGND 10nF 82Ω Figure 1. Direct Conversion Transmitter (Simplified Schematic: All Connections and Decoupling Not Shown) Rev. 0 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 Fax: 781.461.3113 ©2012 Analog Devices, Inc. All rights reserved. CN-0311 Circuit Note The circuit shown in Figure 1 uses the ADF4351, a fully integrated fractional-N PLL IC, and the ADL5385 wideband transmit modulator. The ADF4351 provides the local oscillator (the LO is twice the modulator RF output frequency) signal for the ADL5385 transmit quadrature modulator, which upconverts the analog I/Q signals to RF. Taken together, the two devices provide a wideband, baseband I/Q-to-RF transmit solution. The ADF4351 is powered off the ultralow noise 3.3 V ADP150 regulator for optimal LO phase noise performance. The ADL5385 is powered off a 5 V ADP3334 LDO. The ADP150 LDO has an output voltage noise of only 9 µV rms, integrated from 10 Hz to 100 kHz, and helps to optimize VCO phase noise and reduce the impact of VCO pushing (equivalent to power supply rejection). See CN-0147 for more details on powering the ADF4351 with the ADP150 LDO. The ADL5385 uses a divide-by-2 block to generate the quadrature LO signals. The quadrature accuracy is, thus, dependent on the duty cycle accuracy of the incoming LO signal (as well as the matching of the internal divider flip-flops). Any imbalance in the rise and fall times causes even-order harmonics to appear, as evident on the ADF4351 RF outputs. When driving the modulator LO inputs differentially, even-order cancellation of harmonics is achieved, improving the overall quadrature generation. (See “Wideband A/D Converter Front-End Design Considerations: When to Use a Double Transformer Configuration.” Rob Reeder and Ramya Ramachandran. Analog Dialogue, 40-07.) Because sideband suppression performance is dependent on the modulator quadrature accuracy, better sideband suppression is achievable when driving the LO input ports differentially vs. single-ended. The ADF4351 has differential RF outputs compared to the single-ended output available on most of the competitor’s PLL devices with integrated VCOs. A sweep of sideband suppression vs. RF output frequency is shown in Figure 2. In this sweep, the test conditions were as follows: • Baseband I/Q amplitude = 1.4 V p-p differential sine waves in quadrature with a 500 mV dc bias Baseband I/Q frequency (fBB) = 1 MHz LO = 2 × RFOUT • • A simplified diagram of the test setup is shown in Figure 3. A modified ADL5385 evaluation board was used because the standard ADL5385 board does not allow a differential LO input drive. 0 DATA SHEET SPECIFICATION –10 –20 –30 –40 –50 –60 –70 0 500 1000 1500 2000 FREQUENCY (MHz) 11268-002 CIRCUIT DESCRIPTION The ADF4351 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. Use an inductor value of 19 nH or greater for LO operation below 1 GHz. The measured results in this circuit were performed using ZBIAS = 50 Ω and an output power setting of 5 dBm. When using the 50 Ω resistor, this setting gives approximately 0 dBm on each output across the full band, or 3 dBm differentially. The ADL5385 LO input drive level specification is −10 dBm to +5 dBm; therefore, it is possible to reduce the ADF4351 output power to save current. SIDEBAND SUPPRESSION (dBc) To achieve optimum performance, the only requirement is that the LO inputs of the modulator be driven differentially. The ADF4351 provides differential RF outputs and is, therefore, an excellent match. This PLL-to-modulator interface is applicable to all I/Q modulators and I/Q demodulators that contain a 2XLO-based phase splitter. Low noise LDOs ensure that the power management scheme has no adverse impact on phase noise and error vector magnitude (EVM). This combination of components represents an industry-leading direct conversion transmitter performance over a frequency range of 30 MHz to 2.2 GHz. For frequencies above 2.2 GHz, it is recommended to use a divide-by-1 modulator, as described in CN-0285. Figure 2. Sideband Suppression, RFOUT Swept from 30 MHz to 2200 MHz This circuit achieves comparable or improved sideband suppression performance when compared to driving the ADL5385 with a low noise RF signal generator, as used in the data sheet measurement. Using the differential RF outputs of the ADF4351 provides even-order harmonic cancellation and improves modulator quadrature accuracy. This affects sideband suppression performance and EVM. A single carrier W-CDMA composite EVM of better than 2% was measured with the circuit shown in Figure 1. The solution thus provides a low EVM broadband solution for frequencies from 30 MHz to 2.2 GHz. For frequencies above 2.2 GHz, use a divide-by-1 modulator block, as described in CN-0285. The complete design support package can be found at http://www.analog.com/CN0311-DesignSupport. Rev. 0 | Page 2 of 4 Circuit Note CN-0311 R&S AMIQ IP RFOUTA+ QP QN ADL5385 EVALUATION BOARD ADAPTED TO ACCEPT RFOUT DIFFERENTIAL LO INPUTS ADF4351 EVALUATION BOARD RFOUTA– IN LOIP SPECTRUM ANALYZER LOIN 11268-003 5V POWER SUPPLY Figure 3. Sideband Suppression Measurement Test Setup (Simplified Diagram) COMMON VARIATIONS Getting Started The PLL-to-modulator interface described is applicable to all I/Q modulators that contain a 2XLO-based phase splitter. It is also applicable to 2XLO-based I/Q demodulators, such as the ADL5387. A description of the circuit, the schematic, and a block diagram of the test setup is detailed within the CN-0311 (see Figure 1 and Figure 3). The UG-435 user guide details the installation and use of the EVAL-ADF4351EB1Z evaluation software. The UG-435 also contains the board setup instructions, and the board schematic, layout, and bill of materials. The ADL5385-EVALZ board schematic, block diagram, bill of materials, layout, and assembly information is included in the ADL5385 data sheet. See the ADF4351 data sheet and ADL5385 data sheet for device information. CIRCUIT EVALUATION AND TEST The CN-0311 uses the EVAL-ADF4351EB1Z and the ADL5385EVALZ for the evaluation of the described circuit, allowing for quick setup and evaluation. The EVAL-ADF4351EB1Z uses the standard ADF4351 programming software contained on the CD that accompanies the evaluation board. Equipment Needed Functional Block Diagram The following equipment is needed: The functional block diagram of the described test setup is shown in Figure 3. • Setup and Test • • • • • • A PC with a USB port that contains Windows® XP, Vista, or Windows 7 The EVAL-ADF4351EB1Z evaluation board The ADL5385-EVALZ evaluation board, ADF4351 programming software Power supplies (5 V, 500 mA) An I-Q signal source, such as a Rohde & Schwarz AMIQ A spectrum analyzer After setting up the equipment, use standard RF test methods to measure the sideband suppression of the circuit. Also, see the UG-435 User Guide for the EVAL-ADF4351EB1Z evaluation board, the ADF4351 data sheet, and the ADL5385 data sheet. Rev. 0 | Page 3 of 4 CN-0311 Circuit Note LEARN MORE Data Sheets and Evaluation Boards CN0311 Design Support Package: http://www.analog.com/CN0311-DesignSupport ADF4351 Data Sheet ADIsimPLL Design Tool ADL5385 Data Sheet ADIsimPower Design Tool ADL5385 Evaluation Board ADIsimRF Design Tool ADP150 Data Sheet Brandon, David, David Crook, and Ken Gentile. AN-0996 Application Note, The Advantages of Using a Quadrature Digital Upconverter (QDUC) in Point-to-Point Microwave Transmit Systems. Analog Devices. ADP3334 Data Sheet ADF4351 Evaluation Board REVISION HISTORY 12/12—Revision 0: Initial Version CN-0134, Broadband Low EVM Direct Conversion Transmitter. Analog Devices. CN-0147, Using the ADP150 LDO Regulators to Power the ADF4350 PLL and VCO. Analog Devices. Nash, Eamon. AN-1039 Application Note, Correcting Imperfections in IQ Modulators to Improve RF Signal Fidelity. Analog Devices. Reeder, Rob, and Ramya Ramachandran. “Wideband A/D Converter Front-End Design Considerations: When to Use a Double Transformer Configuration.” Analog Dialogue, 40-07. (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. However, Circuits from the Lab circuits are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so. ©2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN11268-0-12/12(0) Rev. 0 | Page 4 of 4