circuit note cn - 0311 circuits from the lab? reference circuits are engineered and tested for quick and easy system integration to help solve todays analog, mixed - signal, and rf design challenges. for more i nformation and/or support , visit www.analog.com/cn0311 . devices connected /referenced adf435 1 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. 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 des ign 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 f or 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. (cont inued 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. evaluation and desig n support circuit evaluation boards adf435 1 evaluation board (eval - adf4351 eb1z) adl5385 evaluation board (adl5385 - evalz) design and integration 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 30 mhz to 2.2 ghz are supported by us ing 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 - 0 285 ), harmonic filtering of the lo is not required. figure 1. direct conversion transmitter (simplified schematic: all connections and decoupling not shown) 22nf 10nf 330nf 180 ? 82 ? ibbp ibbn loip qbbp qbbn spi-compatible serial bus adf4351 v vco v vco v dd 3.3v cp gnd agnd dgnd rf out b? rf out b+ cp out 1nf 1nf 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 divide-by-2 quadrature phase splitter loin 1nf 1nf 1 1268-001
cn- 0311 circuit note rev. 0 | page 2 of 4 to achieve opti mum performance, the only requirement is that the lo inputs of the modulator be driven differentially. the adf435 1 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 schem e 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 - 0 285. circuit description the circuit shown in figure 1 u s es the adf435 1 , a fully integrated f ractional - n pll ic, and the adl5385 wideband transmit modulator. the adf435 1 provides the local oscillator (the lo is twice the modulator rf output frequency) signal for the adl5385 transmit quadrature modulator, which upconverts the a nalog i/q signals to rf. taken together, the two devices provide a wideband , baseband i/q - to - rf transmit solution. the adf435 1 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 adf435 1 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 fa ll times causes even - order harmonics to appear, as evident on the adf435 1 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 adf435 1 has differential rf outputs compared to the single - ended output available on most of the competitor s pll devices with integrated vco s. the adf435 1 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 resistive load (z bias = 50 ? ) or a resistive in parallel with a reactive load for z bias . the latter gives slightly higher output powe r, 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 set ting 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 adf435 1 output power to save current. a sweep of sideband suppression vs . rf output frequency is shown in figure 2 . in this sweep, the test conditions were as follows: ? b aseband i/q amplitude = 1.4 v p - p differential sine waves in quadrature with a 500 mv dc bias ? b aseband i/q frequency (f bb ) = 1 mhz ? lo = 2 rf out a simplified diagram of the test setup is shown in figure 3 . a modified adl5385 evaluation boar d was used because the standard adl5385 board does not allow a differential lo input drive. figure 2. sideband suppression , rfout s wept 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 differen tial rf outputs of the adf435 1 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 broad - band solution for frequen cies from 30 mhz to 2.2 ghz. for frequencies above 2.2 ghz, use a divide - by - 1 modulator block, as described in cn - 0 285 . the complete design support package can be found at http://www.analog.com/cn0311 - designsupport . 0 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 500 1000 1500 2000 sideband suppression (dbc) frequency (mhz) data sheet specification 1 1268-002
circuit note cn- 0311 rev. 0 | page 3 of 4 figure 3. sideband suppression measurement test setup (simplified diagram) common variations 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 . circuit e valuation and t est the cn - 0311 uses the eval - adf435 1 eb1z and the adl5385 - evalz for the evaluation of the described circuit, a llowing for quick setup and evaluation. the eval - adf4351 eb1z uses the standard adf435 1 progra m ming software contained on the cd that accompanies the evaluation board. equipment needed the following equipment is needed: ? a pc with a usb port that contains w i n d o w s ? x p, vista , or windows 7 ? t he e va l - adf4351 eb1z evaluation board ? t he adl5385 - e va l z evaluation board , ? adf435 1 programming software ? p ower supplies (5 v, 500 ma) ? a n i - q signal source, such as a roh de & schwarz amiq ? a spectrum analyzer also, s ee the ug - 435 user guide for the ev al - adf435 1 eb1z evaluation board, the adf4351 data sheet, and the adl5385 data sheet. getting started a description of the circuit, the schematic, and a block diagram of the test setup is detailed with in the cn - 0311 (see figure 1 and figure 3 ) . the ug - 435 user guide details the installation and use of the e va l - adf435 1 eb1z evaluation software. the ug - 435 also contains the board setup instruc tions , and the board schematic , layout, and b ill of m aterial s . the adl5385 - eva l z board schematic, block dia gram, bill of m aterials, layout , and assembly information is included in the adl5385 data sheet. see the adf435 1 data sheet and adl5385 data sheet for device information. functional block diagram the function al block d iagram of the described test setup is shown in figure 3 . setup and test after setting up the equipment, use standard rf test methods to measure the sideband suppression of the circuit. r&s amiq power supp l y adl5385 evaluation board adapted to accept differential lo inputs adf4351 evaluation board spectrum analyzer i p loi p loin rf out a+ rf out a? rfout in q p qn 5v 1 1268-003
cn- 0311 circuit note rev. 0 | page 4 of 4 learn more cn0 311 design support package: http://www.analog.com/cn0311 - designsupport adisimpll design tool adisimpower design tool adisimrf design tool brandon, david, david crook, and ken gentile. an - 0996 application no te, the advantages of using a quadrature digital upconverter (qduc) in point - to - point microwave 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 mod ulators 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. a nalog dialogue , 40- 07. data sheets and evaluation boards adf435 1 data sheet adf435 1 evaluation board adl538 5 data sheet adl5385 evaluation board adp15 0 data sheet adp333 4 data sheet revision history 1 2 / 12 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 other wise 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. howev er, circuits from the lab circuits are supplied "as is" and without warranties of any kind, express, implied, or statutory includin g, 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 right s 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 s o. ? 2012 analog devices, inc. all right s reserved. trademarks and registered trademarks are the property of their respective owners. cn11268 - 0 - 12/12(0)
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