circuit note cn - 0144 circuits from the lab? tested circuit designs address co m mon design challenges and are engineered for quick and easy system integration. fo r more information and/or support, visit www.analog.com/cn0144 . devices connected /referenced adf4350 fractional - n pll ic with i ntegrated vco adl5385 wideband transmit modulator ADP150 low noise 3.3 v ldo adp3334 low noise a djustable ldo broadband low error vector magnitude (evm) direct conversion transmitter using lo divide - by - 2 modulator rev. c circuits from the lab? circuits from analog devices have been designed and built by analog devices engine ers. 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 testin g 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 c onnected 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 ? 2010 C 2012 analog devices, inc. all rights reserved. evaluation and desig n support circuit evaluation boards adf4350 evaluation board (eval - adf4350 - eb1z) adl5385 evaluation board (adl5385 - evalz) design and integra tion files schematics, layout files, bill of materials circuit function and benefits this circuit is a complete implementation of the analog portion of a broadband direct conversion transmitter (analog baseband in, rf out). rf frequencies from 68.75 mhz to 2.2 ghz are su p ported through the use of a pll with a broadband integrated voltage controlled oscillator (vco). unlike modulators that use a divide - by - 1 lo stage (as described in cn- 0134 ), harmonic filtering of the lo is not required. 22nf 10nf 330nf 180 ? 82 ? ibbp ibbn loip qbbp qbbn spi-compatible serial bus adf4350 v vco v vco v dd 3.3v cp gnd agnd d gnd rf out b? rf out b+ cp out 1nf1nf 4.7k ? r set le data clk ref in fref in v tune dv dd av dd ce 10 28 16 29 1 2 3 22 8 31 9 11 18 21 27 51 ? a gndvco 14 15 17 20 7 pdb rf 26 sd gnd 6 32 sdv dd v p 5 sw 4 ad l 538 5 r fout rf out a? rf out a+ 13 12 v vco z bias z bias i/q sma inputs i/q sma inputs ADP150 1f 1f 5.5v 5.0v vps1, vps2 adp3334 1f 1f 5.5v 08835-001 divide-by-2 quadrature phase splitter loin 1nf 1nf figure 1. direct conversion transmitter (simplified schematic: all connections and decoupling not shown)
cn-0144 circuit note rev. c | page 2 of 4 to achieve optimum pe rformance , t he only requirement is that the lo inputs of the modulator be driven differentially. the adf4350 provides di f ferential rf outputs and is, therefore, an excellent match. this pll - to - modulator interface is applica ble 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 ve c tor magnitude (evm). this combination of components represents industry - leading direct conversion transmitter performance over a frequency range of 68.75 mhz to 2.2 ghz. for frequencies above 2.2 ghz , it is reco m mended to use a divide - by - 1 modulator, as described in cn - 0134. circuit description the circuit shown in figure 1 utilizes the adf4350 , a fully integrated fractional - n pll ic, and the adl5385 wideband transmit modulator. the adf4350 provides the local oscillator (the lo is twice the modulator rf output frequency) signal for the adl5385 transmit quadrature modu lator, which upconverts analog i/q signals to rf. taken together , the two devices provide a wid e band baseband i/q - to - rf transmit solution. the adf4350 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 v 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 adf4350 with the ADP150 ldo. the adl5385 uses a divide - by - 2 block to generate the quadr a ture 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 e ven order harmonics to a p pear, as evident on the adf4350 rf outputs. when driving the modulator lo inputs differentially, even - order cancellation of harmonics is achieved, improving the overall quadrature ge ne ration. (see wideband a/d converter front - end design considerations: when to use a double transformer configur a tion. 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. si n gle - ended. the adf4350 has differential rf outputs compared to a single - ended output available on most compet i tor pll devices with integrated vco. the adf4350 output match consists of the z bias 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 resi s tive load (z bias = 50 ? ) or a resistive in parallel with a reactive load for z bias . the latter gives slightly higher output power, depending on the inductor chosen. use a n inductor value of 19 nh or greater for lo operation below 1 ghz. the measured results in this circuit were performed using z bias = 50 ? and an output power setting of 5 dbm. when using the 50 ? resistor, this setting gives approximately 0 dbm on eac h output across the full band, or 3 dbm differentially. the adl5385 lo input drive level specification is ? 10 dbm to +5 dbm; therefore, it should be possible to reduce the adf4350 ou t p ut power to save current . a sweep of sideband suppression v ersus 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 s ine wa ves in quadrature with a 500 mv dc bias; baseb and i/q frequency (f bb ) = 1 mhz; lo = 2 rfout. a simplified diagram of the test setup is shown in figure 3 . a modified adl5385 ev aluation board was used because the standard adl5385 board does not allow a differential lo input drive. 0 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 500 1000 1500 2000 2500 sideband suppression (dbc) frequency (mhz) 08835-002 adf4350 as lo source differential connection data sheet specification figure 2. sideband suppression , rfout s wept from 68.75 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 adf4350 provides even - order harmonic cancellation and improves modulator quadrature accuracy. this impacts sideband suppression performance and evm (error vector magnitude). a s ingle 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 68.75 mhz to 2.2 ghz. for frequencies above 2.2 ghz, a divide - by -1 modulator block should be used, as d e scribed in cn - 0134 . a complete design support package for this circuit note can be found at http:// www.analog.com/cn0144- designsupport .
circuit note cn-0144 rev. c | page 3 of 4 r&s amiq power supp ly ad5385 evaluation board adapted to accept differential lo inputs adf4350 evaluation board spectrum analyzer ip loi p loin rf out a+ rf out a? rfout in qp qn 5v 08835-003 figure 3. sideband suppression measurement test setup (simplified diagram) common variations the pll - to - modulator interface described in this circuit note is applicable to all i/q modula tors that contain a 2xlo - based phase splitter. it is also applicable to 2xlo - based i/q demod u lators such as the adl5387 . circuit e valuation and t est the cn - 0144 us es the eval - adf4350eb1z and the adl5385 - evalz boards for evaluation of the described ci r cuit, a llowing for quick setup and evaluation. the eval - adf4350eb1z board uses the standard adf4350 progra m ming software , contained on the cd that accompanies the evaluation board. equipment needed windows? xp, windows vista (32 - bit), or windows 7 (32 - bit ) pc with usb port, the eval - adf4350eb1z , and the adl5385 - evalz circuit evaluation boards , the a df4350 pr o gramming software , power supplies, i- q signal source, such as a rhode & schwarz amiq, and a spectrum analyzer. see th e cn - 0144 and the ug - 109 user guide for e valua tion b oard eval - adf4350eb1z and the adf4350 and adl5385 data sheets. getting started th is circuit note contains a description of the circuit, the sch e matic , and a block diagram of the test setup. the user g uide ug - 109 details the installation and use of the e va l - adf 4350 evaluation software. the ug - 109 also contains board setup instru c tions and the board schematic, layout, and b ill of m aterial s . the adl5385 - evalz board schem atic, block dia gram, bill of m at e rials, layout , and assembly information is included in the adl5385 data sheet. see the adf4350 and adl5385 data sheet for device information. functional block diagram the cn - 0144 contains the function block d iagram of the described test setup in figure 3 . s etup and test after setting up the equipment, use standard rf test methods to measure the sideband suppression of the ci r cuit. further improvements w ith filtering the sideband suppression of this circuit can be further improved by filtering the lo signal before the loip and loin pins of the adl5385 . filtering attenuate s harmonic levels so as to minimize errors in the quadrature generation block of the adl5385 . at some frequencies, this can result in improvements over 10 db. however, using a filter will limit the bandwidth of the circuit. see figure 4 for narrowband results. ?80 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 700 800 900 1000 1 100 1200 1300 sideband suppression (dbc) rf out (mhz) no f il ter with f il ter 08835-004 figure 4 . sideband suppression comparis on w ith and w ithout a h armonic f ilter the lo signal was passed through a low - pass filter with a 3 db point at approximately 2600 mhz. this results in a usable output frequency up to approximately 1300 mhz.
cn-0144 circuit note rev. c | page 4 of 4 learn more cn0 144 design support package: http://www.analog.com/cn0144-designsupport adisimpll design tool adisimpower design tool adisimrf design tool brandon, david, david crook, and ken gentile. an - 0996 application note, the advantages of using a quadrature digital upconverter (qduc) in point - to - point micro wave transmit systems. analog devices. 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. data sheets and evaluation boards adf435 0 data sheet adf4350 evaluation board adl538 5 data sheet adl5385 evaluation board adp15 0 data sheet adp333 4 data sheet revision history 10 /12 rev. b to rev. c added further improvements with filtering section .................. 3 11/10 rev. a to rev. b changes to circuit note title .......................................................... 1 added evaluation and design support section ............................ 1 changes to figure 3 ........................................................................... 3 added circuit evaluation and test section ................................... 3 8/10 rev. 0 to rev. a changes to circuit function and benefits section ....................... 1 changes to circuit description section ......................................... 2 added common variations section ............................................... 3 3/ 10 revision 0 : initial version (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 intellectua l 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 circu its from the lab circuits at any time without notice but is under no obligation to do so. ? 2010 C 2012 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. cn08835 -0- 10/12(c)
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