circuit note cn - 0245 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 information and/or support, visit www.analog.com/cn0245 . devices connected/referenced adf435 0 wideband synthesizer with integrated vco adl5387 50 mhz to 2 ghz quadrature demodulator adl5380 400 mhz to 6 ghz quadrature demodulator wideband lo pll synthesizer with simple interface to q uadrature demodulator s rev. 0 circuits from the lab? circu its 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 f or 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 ? 2011 analog devices, inc. all rights reserved. evaluation and desig n support circuit evaluation boards adl5387 evaluation board (adl5387 - evalz) adl5380 evaluation board (adl5380 - 30a - evalz ) cn0134 evaluation platform (cftl - cn0134 - evalz) design and integration files schematics, layout files, bill of materials circuit function and benefits the circuit , shown in figure 1 , highlights the ease of interfacing the adf4350 wideband synthesizer with integrated vco with the adl5380 and adl5387 wideband i/ q demodulators . in this circuit, the adf4350 provides the high frequency , low phase noise local oscillator ( lo ) signal to the wideband i/ q demodulator. this circuit configuration of fers quite a few benefits that make it an attractive solution in applications requiring quadrature mixing down to baseband or to an intermediate frequency. the adf4350 offers rf differential output s and , likew ise , the adl5380 / adl5387 accept differential inputs. this interface offers both ease of use and performance advantage s . the differential signal configuration prov id es common - mode noise reduction and even order cancellation of the lo harmonics , which maintains the quadrature accuracy of the i / q de modulators . additionally, the output power level of the adf4350 matches the input power requirements of the quadrature demodulators very well . as a result , an lo buffer is not necessary. the adf4350 outputs cover a wide frequency range from 137.5 mhz to 4400 mhz. the adl5387 frequency range spans from 50 mhz to 2 ghz , and the adl5380 covers t he higher frequency range from 4 00 mhz to 6 ghz . between the adl5380 and adl5387 the rf input range can span from 50 mhz to 6 ghz . therefore , the two chip circuit configuration as shown in figure 1 offers coverage of a wide frequency ran ge from 50 mhz to 4400 ghz. 0 90 loip loin adf4350 adl5380/adl5387 quadrature demodulator wideband synthesizer rf out a+ rf out aC lpf 3.3v rf+ rfC q+ qC i+ iC z bias z bias 10224-001 figure 1. simple interface between the adf4350 pll synthesizer and the adl5380 or adl5387 quadrature demodulator (simplified schematic: all connections and decoupling not shown)
CN-0245 circuit note rev. 0 | page 2 of 5 circuit description the adf4350 is a wideband fractional - n and integer - n phase - locked loop frequency synthesizer covering the frequency range of 137.5 mhz to 4400 mhz . the adf4350 has an integrated voltage controlled oscillator (vco) with a fundamental frequency range of 2200 mhz to 4400 mhz . th e adf4350 offers high quality synthesizer performance . however , depending on the demodulator architecture , lo filtering may be required to minimize the effects of harmonics from the pll on the quadrature accurac y of the i / q demodulator . analog devices offer s quadrature demodulators that cover a wide frequency range . the adl5387 frequency range spans from 50 mhz to 2 ghz , and the adl5380 covers t he higher frequency range from 4 00 mhz to 6 ghz . t he adl5387 and adl5380 utilize two different architectures to generate the 90 phase s hift between the i and q paths . the adl5387 utilizes a 2 lo architecture where the local oscillator is at twice the rf frequency , while the adl5380 uses a poly phase filter - based phase splitter . the polyphase architecture has a narrower fractional bandwidth (i.e. , operates across less octaves) and is more sensitive to pll harmonics compared to a 2 lo - based phase splitter. as a result, the adl5380 requires harmonic filtering of the lo to maintain the quadrature accuracy of the i / q demodulator , while filtering is only required for the 2 lo - based adl5387 at the top end of its frequency range. d q q lo_in ck d q q ck lo_i (0) lo_q (90) 10224-002 figure 2. simplified 2 lo -based phase splitter figure 2 shows a simplified 2 lo phase splitter as implemented in the adl5387 . t he 90 phase split of the lo path is achieved via digital circuitry that uses d - type flip - flops and an inverter . this architecture requires an external lo operating at twice the frequency of the desired lo . lo_i (0) lo_q (90) lo_in 10224-003 figure 3 . simplifie d first order polyphase filter figure 3 shows a simplified first order polyphase circuit, as implemented in the adl5380 . the polyphase circuit consists of complementary rc subcircui ts that create a low - pass transfer function from input to one output , and a high - pass transfer function to the other output . if the r and c values of the two polyphased paths are matched, then both paths have the same corner frequency and , more importantly , the phase of one output tracks the other with a 90 phase shift. interfacing the adf4350 pll with the adl5387 i/ q demodulator the adl5387 and adl5380 i/ q demodulators utilize different architectures to achieve the ultimate goal of generating precise quadrature signals . when interfacing with an lo synthesizer like the adf4350 , it is important to consider how the architectures respond to the lo signal and its harmonics. t his will determine the requirement for lo filtering . figure 4 shows the basic inte rface between the adf4350 and adl5387 . depending on the frequency of operation , an lo harmonic filter may or may not be required between the adf4350 and adl5387 . adf4350 wideband synthesizer rf out a+ rf out aC 3.3v z bias z bias 12 13 adl5387 quadrature demodulator loip loin 3 4 10224-004 figure 4. adf4350 pll interface to the 2 lo -based phase splitter of the adl5387 demodula tor in a 2 lo - based phase splitter, the quadrature accuracy is dependent on the duty cycle accuracy of the incoming lo . t he matching of the internal divider flip - flops also affects quadrature accuracy but to a much lesser extent. so a 50% duty cycle of the externally applied lo is critical for minimizing quadrature errors. additionally, any imbalance in the rise and fall times causes even order harmonics to appear. when driving the d emodulator lo inputs different ially , even order cancellation of the harmon ics is achieved and results in improved overall quadrature generation.
circuit note CN-0245 rev. 0 | page 3 of 5 with a target image suppression of ?40 dbc, figure 5 shows the performance of the adl5387 with t he adf4350 providing the differential lo source with and without filtering. the blue signal trace representing the signal generator is the ideal case where the lo is generated using a rhode & schwarz signal ge nerator with a sinusoidal output and much lower harmonic levels compared to the adf4350 . this is the ideal case and the target comparison point. from figure 5, it can be seen that filtering is not required at fr equencies below 1 ghz. however , above 1 ghz small errors due to harmonics of the lo become a larger percentage of the input period. in this case , filtering should be used to further attenuate the even order harmonics of the lo and so that the i / q demodulat ors specified quadrature accuracy can be achieved. C20 C70 425 1225 10224-005 image rejection (dbc) rf frequency (mhz) C25 C30 C35 C40 C45 C50 C55 C60 C65 525 625 725 825 925 1025 1125 adf4350, no filter signal generator adf4350 + filter figure 5. adl5387 image rejection vs. rf frequency adf4350 wideband synthesizer rf out a+ rf out aC lpf 3.3v z bias z bias 12 13 adl5380 quadrature demodulator loip loin 3 4 10224-006 figure 6 . adf4350 i nter face to the polyphase filter architecture of the adl5380 demodulator interfacing the adf4350 pll with the adl5380 quadrature demodulator unlike the adl5387 , the polyphase architecture of the adl5380 's phase splitter requires filtering of the adf4350 outputs, as shown in figure 6. filtering is required to attenuate the odd order harmonic s of the lo to minimize errors in the quadrature generation block of the adl 5380. from measurement and simulation as explained in cn- 0134 , the odd order harmonics contribute more than even order harmonics to quadrature errors . figure 7 shows the measurement r esults when the adf4350 outputs are filtered before they are applied to the differential lo inputs of the adl5380 . after filtering , the resulting image rejection is comparable to what is achievable from a low harmonic sig nal generator . C10 C70 850 10224-007 C20 C30 C40 C50 C60 1350 1850 2350 image rejection (dbc) rf frequency (mhz) adf4350, no filter signal generator adf4350 + filter figure 7 . adfl5380 image rejection vs. frequency. filtering requirements in summary, lo filtering the adf4350 outputs to suppress the harmonics of the fundamental helps to maintain the phase accuracy of the quadrature signals of the demodulator . in the case of the adl5380 , which uses a polyphase architecture, filtering is a requirement . the adl5387 architecture consist s of digital circuitry which is more immune to the harmonics of the lo signal . t herefore filtering may not be required , depending on th e frequency of operation . in the case where filtering is necessary, figure 8 , shows an example lo output filter schematic , and table 1 , summarizes the filter component values . this circuit is flexible and provides four different filter options to cover four different bands the filters were designe d for a 100 differential input and 50 differential output to match the lo input requirements of the demodulator . a chebyshev response was used for optimal filter roll - off at the e xpense of increased pass - band ripple . please refer to cn - 0134 for a more detailed discussion on the filtering of the adf4350 outputs.
CN-0245 circuit note rev. 0 | page 4 of 5 table 1 . adf4350 rf output filter component value (dni = do not insert) frequenc y range (mhz) z bias l1 (nh) l2 (nh) c1a (pf) c1c (pf) c2a (pf) c2c (pf) c3a (pf) c3c (pf) a . 500C 1300 27 nh|| 50 ? 3.9 3.9 dni 4.7 dni 5.6 dni 3.3 b . 850C 2450 19 nh || (100 ? in position c1c) 2.7 2.7 3.3 100 ? 4.7 dni 3.3 dni c . 1250C 2800 50 ? 0 ? 3.6 dni dni 2.2 dni 1.5 dni d . 2800C 4400 3.9 nh 0 ? 0 ? dni dni dni dni dni dni 120pf 120pf 0.1f z bias z bias loip loin adl5380 adf4350 rf out a+ rf out aC 3.3v c1a c2a c3a c1a c2a c3a c1c c2c c3c 1nf 1nf l1 l2 l1 l2 12 13 3 4 10224-008 figure 8 . adf4350 rf output filter schematic common variations the interface discussed above is applicable to any pll with differential lo outputs and to any 1 lo or 2 lo - based i / q d emodulator. the adl5382 is a 1 lo - based i / q d emodulator that operates from 700 mhz to 2700 mhz and provides slightly higher ip3 than the adl5380 . the ad8347 (1 lo) and ad8348 (2 lo) are lower power i / q d emodulators that integrate front - end variable gain amplifiers and fixed - gain baseband amplifiers. circuit evaluation a nd test the circuit s shown in figure 4 and figure 6 were implemented using the cn - 0134 evaluation board ( cftl - 0134evalz ) and the adl5387 or adl5380 evaluation board s. the cn - 0134 evaluation platform includes the adf4350 , pads for an lo filter , and differential lo outputs to sma connectors . the adf4350 must be programmed, and the software is contained on the cd that accompanies the evaluation board . table 2 provides the ordering guide for the various evaluation boards. the cn - 0134 evaluation board is configured by default to an 850 mhz to 2450 mhz filter design as s pecified in table 1. to implement an alternative filter, the appropriate components must be swapped out. table 2 . evaluation board information evaluation board adl5387 adl5387 - evalz adl5380 low b and (400 mhz to 3 ghz) mid band (3 ghz to 4 ghz) adl5380 - 30a - evalz adl5380 - 29a - evalz cn - 0134 cftl -0134 - evalz euipment needed ? windows xp, windows vista (32 - bit) , or windows 7 (32 - bit) pc with usb p ort ? evaluation boards as listed in table 2 ? rf source ( rohde & schwarz smt06 or equivalent) ? spectrum a nalyzer ( rohde & schwarz fsea30 or equivalent) ? power supplies : ? a dl5387 - e va l z : +5 v ? adl5380 - 30a - e va l z : +5 v ? cftl - 0134- e va l z : +5.5 v test the cn - 0134 evaluation pl atform allow s easy evaluation and has an integrated crystal oscillator on board. a pc with the adf4350 software is required to program the synthesizer to the desired lo frequency. the adl5387 / adl5380 qu adrature demodulator will down convert the rf frequency to baseband. the differential i and q baseband outputs are applied to the fsea spectrum analyzer in the fft mode, an d image rejection is measured. additional documentation can be found in the following design support packages for cn - 0245, cn - 0134 , and cn - 0144 : cn - 0245 design support package: www.analog.com/cn0245- designsupport cn - 0134 design support package: www.anal og.com/cn0134 - designsupport cn - 0144 deign support package: www.analog.com/cn0144- designsupport
circuit note CN-0245 rev. 0 | page 5 of 5 pc controller usb lo+ rf +5.0v +5.5v loC adl5380 or adl5387 evaluation board cn-0134 evaluation platform (cftl-0134-evalz) i+ iC q+ qC rohde & sch w arz smt06 signa l gener at or rohde & sch w arz fsea30 spectrum ana lyzer agilent e3631 power supp ly 10224-009 figure 9 . f unctional block diagram of test setup learn more nash, eamon, an - 1039 application note. correcting imperfections in iq modulators to improve rf signal fidelity . analog devices. cn - 0245 design support package: www.analog.com/cn0245- designsupport cn - 0134 design support package: www.analog.com/cn0134- designsupport cn - 0144 de s ign support package: www.analog.com/cn0144- designsupport adisimrf design tool adisim pll design tool data sheets and evaluation boards adl5387 data sheet and evaluation board adl5380 data sheet an d evaluation board adf4350 data sheet and evaluation board revision history 12/ 11 rev ision 0: initial version (continued from first page) circuits from the lab circuits are intended only for use with anal og 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 o t h erwise 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 designs are supplied "as is" and without warranties of any k ind, 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 p atents 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 s o. ? 2 011 a nalog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. c n 10224 -0- 12/11(0)
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