circuit note cn - 02 85 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/ cn0285 . devices connected /referenced adf4351 fractional - n pll ic with i ntegrated vco ADL5375 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 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 dam ages 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 ? 2013 analog devices, inc. all rights reserved. evaluation and desig n support circuit evaluation boards cn - 0285 evaluation board ( eval - cn0285 - eb1z ) design and integration files schematic s, 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 500 mhz to 4.4 ghz are supported using a phase - locked loop ( pll ) with a broadband , integrated voltage controlled oscillator (vco). harmonic filtering of the local oscillator ( lo ) from the pll ensures excellent quad rature accuracy , sideband suppression , and low evm . figure 1. direct conversion transmitter (simplified schematic: all connections and decoupling not shown) 2.7nf 680pf 47nf 1k ? 360 ? ibbp ibbn loip loin 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 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 537 5 r fout rf out a? rf out a+ 13 12 v vco z bias z bias quadrature phase splitter i/q sma inputs i/q sma inputs adp150 1f 1f 5.5v 5.0v vps1, vps2 adp3334 1f 1f 5.5v 10921-001
cn-0285 circuit note rev. 0 | page 2 of 5 figure 2. evaluation board for cn - 0285 direct conversion transmitter low noise , low dropout regulators ( 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 us es the adf4351 , a fully integrated fractional - n pll ic, and the adl53 75 wideband transmit modulator. the adf4351 provides the lo signal for the ADL5375 transmit quadrature modulator, which upconverts analog i/q signals to rf. taken t ogether, the two devices provide a wideband , baseband iq - to - rf transmit solution. the adf4351 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 v 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 adf4351 rf o utputs to attenu ate harmonic levels to minimize errors in the quadrature generation block of the ADL5375 . from measurement and simulation, the odd - order harmon ics contribute more than even - orde r harmonics to quadrature error and , if attenuated to below ? 30 dbc , results in sideband suppression performance of ? 40 dbc or better. the second harmonic (2h) and third harmonic (3h) levels of the adf4351 are as given in the data sheet and shown in table 1 . to get the thir d harmonic below ? 30 dbc, approximately 20 db of attenuation is required. table 1 . adf4351 rf o utput h armonic l evels u nfiltered harmonic content value (dbc) description second ?19 fundamental vco output third ?13 fundamental vco output second ?20 divided vco output third ?10 divided vco output this circuit gives four different filter options to cover four different bands. the filters were designed wit h a 100 ? differential input ( adf4351 rf outputs with appropriate matching) and a 50 ? 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 minimi z e 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 re duced. for lower frequencies (< 2 ghz), a fully differential filter provides adequate results. table 2 . adf4351 rf output f ilter c omponent v alues (dni = d o n ot i nsert) frequency range (mhz) z bias l1 (nh) l2 (nh) c1a (pf) c1c (pf) c2a (pf) c2c (pf) c3a (pf) c3c (pf) 500 to 1300 (filter type a) 27 nh||50 ? 3.9 3.9 dni 4.7 dni 5.6 dni 3.3 850 to 2450 (filter type b) 19 nh||(100 ? in p osition c1c) 2.7 2.7 3.3 100 ? 4.7 dni 3.3 dni 1250 to 2800 (filter type c) 50 ? 0 ? 3.6 dni dni 2.2 dni 1.5 dni 2800 to 4400 (filter type d) 3.9 nh 0 ? 0 ? dni dni dni dni dni dni 10921-002
circuit note cn - 0285 rev. 0 | page 3 of 5 the adf4351 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 power, depending on the inductor chosen. note that it is possible to place the parallel resistor as a differential component ( that is, 100 ?) in p osition c1c to minimize board space (see filter type b, table 2 ). design t he filter with a cutoff approximately 1.2 times to 1.5 times the highest frequency in the band of interest. this cutoff allows margin in the design, becaus e typically the cutoff is lower than designed due to parasitics. the effect of printed circuit board (pcb) parasitics can be simulated in an electromagnetic ( em ) simulation tool for improved accuracy. figure 3 . adf4351 rf output filter schematic as can be seen from table 2 , at frequencies lower than 1250 mhz, a fif th - order filter i s required. for 1.25 ghz to2.8 ghz, thir d- order filtering is sufficient. for frequencies more than 2.8 ghz, filtering is not required because the harmonic levels are sufficiently low to meet the sideband suppression specifications. figure 4 . sideband suppression for filter type b , 850 mhz to 2450 mhz figure 5 . evm plot a sweep of sideband suppression vs. frequency is shown in figure 4 for the circuit using filter type b (8 00 mhz to 2400 mhz). in this sweep, the test conditions were the following: ? b aseband i/q amplitude = 1 v p - p differential sine waves in q uadrature with a 500 mv ( ADL5375 - 05 ) dc bias ? b aseband i/q frequency (f bb ) = 1 mhz. 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 conste llation points from their ideal locations, due to both magnitude and phase errors (see figure 5 ). evm measurements are given in table 3 comparing the results with and without the filter. in this case , the baseband i/q signals were generated using 3gpp test m odel 4 using a ro h de & schwarz amiq i/q modulation generator with differential i and q analog outputs. filter type b was also used. a block diagram of the test setup for the evm is shown in figure 6 . for comparative purposes , the adf4350 is also measured. lower evm due to in - band pll noise improvements on the adf4351 can be seen i n table 3 . other contributing factors to the evm improvement are the lower phase frequency detector ( pfd ) spurious levels on the adf4351 . adf4351 12 rf out a+ 13 rf out a? ADL5375 3 loip 4 loin l1 l2 1nf l1 l2 1nf c1a c1a c1c c2a c2a c2c c3a c3a c3c z bias z bias 120pf 120pf 0.1f 3.3v 10921-003 ?70 ?65 ?60 ?55 ?50 ?45 ?40 ?35 ?30 ?25 ?20 800 1000 1200 1400 1600 1800 2000 2200 2400 sideband suppression (dbc) carrier frequenc y (mhz) 5db m fi l ter b: 850mhz t o 2450mhz 10921-004 q i error vector measured signal phase error (i/q error phase) magnitude error (i/q error phase) ideal signal (reference) 0 10921-005
cn - 0285 circuit note rev. 0 | page 4 of 5 table 3. single -c arrier w - cdma composite evm results comparing filter vs. n o filter on adf4351 rf outputs (measured as per 3gpp s pecification test m odel 4 ) frequency (mhz) adf4350 composite evm no lo filtering adf4350 composite evm with lo filtering, filter b adf4351 composite evm with lo filtering, filter b 2140 3.27% 1.31% 1.02% 1800 1.46% 1.13% 0.95% 900 10.01% 1.03% 0.96% figure 6 . evm measurement setup (simplified diagram ) in addition to the improvement in sideband suppression and evm , there is also a performance benefit to driv ing the ADL5375 lo inputs differentially. this benefit improves modulator output ip2 performance by 2 db to 5 db, compared with single - ended lo drive. note that most external vcos only come with a single - ended output, so using the differential outputs on the adf4351 provides a benefit over an external vco in this case. figure 7 shows sideband suppression results using an 8 5 0 mhz to 2450 mhz filter (f ilter type b ). figure 7 . sideband suppression results for 850 mhz to 2450 mhz filter type b a complete design support package for this circuit note can be found at http://www.analog.com/ cn0285 - designsupport . c ommon variations it is possible to use the auxiliary outputs on the adf4351 to switch between two filter types where wideband operation beyond that possible with one single filter is required (see figure 8 ). a n rf d ouble -p ole , 4-t hrow switch (dp4t) is used to selec t the differential outputs of either filter 1 or filter 2. figure 8 . application d iagram s howing p ossibility of f ilter switching u sing the adf4351 m ain and a uxiliary outputs circuit e valuation and t est the eval - cn0285 - eb1z evaluation board con tains the circuit described in cn - 0285 , allowing for the quick setup and evaluation of the performance of the circuit . the control software for the eval - cn0285 - eb1z uses the standard adf4351 programming software located on the cd that acc ompanies the evaluation board. equipment needed the following equipment is needed: ? a standard pc running windows? xp, windows vista (32 - bit), or windows 7 with a usb p ort ? t he eval - cn0285 - eb1z circuit evaluation board ? t he adf 435 x programming software ? 5.5 v p ower supplies ? an i- q signal source, such as the ro h de & schwarz amiq ? a s pe ctrum analyzer , such as the ro h de & schwarz fsq8 for a dditional details , see the ug - 521 user guide , the adf4351 data sheet, and the ADL5375 data sheet. r&s amiq gen. i+ i? q+ q? spectrum analyzer [r&s fsq 8] power supply cn-0285 evaluation board 5.5v rf out 10921-006 ?90 ?80 ?70 ?60 ?50 ?40 ?30 ?20 800 1000 1200 1400 1600 1800 2000 2200 2400 sideband suppression (dbc) carrier frequenc y (mhz) ?4 dbm ?1 dbm +2 dbm +5 dbm 10921-007 adf4351 12 rf out a+ 13 rf out a? 14 rf out b+ 15 rf out b? ADL5375 3 loip 4 loin 1nf 1nf filter 1 dp4t switch filter 2 10921-008
circuit note cn-0285 rev. 0 | page 5 of 5 getting started see the ug - 521 user guide for software installation and test setup. the user guide also includes the block diagram, the application s chematic, the b ill of m aterials, and the layout and assembly information. in addition, see the adf4351 data sheet and the ADL5375 data sheet for additional details. functional block diagram see figure 1 and figure 6 in this document, and also see the ug - 521 user guide . setup and test after setting up the equipment, use standard rf test methods to measure the sideband suppression of the circuit. learn more cn0285 design support package: http://www.analog.com/ cn0285 -designsupport 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. an - 1039 application note. correcting imperfections in iq modulators to improve rf signal fidelity . analog devices. data sheets and evaluation boards adf4351 data sheet adf4351 evaluation board ADL5375 data sheet ADL5375 evaluation board adp150 data sheet adp3334 data sheet revision history 2 /13 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 an alog devices or its licensors. while you may use the circuits from the lab circuits in the design of yo ur 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 a nd no responsibility is assumed by analog devices for their use, nor for any infringements of patents or other rights of thir d parties that may result from their use. analog devices reserves the right to change any circuits from the lab circuits at any tim e without notice but is under no obligation to do so. ? 2013 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. c n 10921 -0- 2 /13(0)
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