circuit note cn - 0283 circuits from the lab? reference circuits are engineered and tested for quick and easy system i ntegration to help solve todays analog, mixed - signal, and rf design challenges. for more i nformation and/or support , visit www.analog.com/cn0283 . devices connected /referenced ad l5375 400 mhz to 6 ghz broadband quadrature modulator ad l5320 400 mhz to 2700 mhz ? watt rf driver amplifier providing fixed power gain at the output of an iq 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 design and construction o f 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 applic ation. 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. evaluation and desig n support circuit evaluation boards ADL5375 evaluation board ( ADL5375 - 05 - evalz) design and integration files schemati cs, layout files, bill of materials circuit function and benefits whether an iq m odulator is used in a direct conversion application or as an upconverter to a first intermediate frequency ( if), some gain is generally applied directly after the iq m odulato r. h ow to choose an appropriate driver amplifier to provide the first stage of gain at the output of an iq m odulator will be described . the devices shown in figure 1 are the ADL5375 iq m od ulator and the adl5320 driver amplif ier . they are well matched from a system performance level; that is, they have equivalent performance so neither device contributes to degradation in the overall perfor mance. because these devices are well matched in terms of their dynamic ranges, a simple direct connection between the iq m od ulator and the rf driver a mplifier is recommended without any need for attenuation between the devices. ib bp ibbn u1 ad l 537 5 loip loin qbbn qb bp q uadrature ph ase splitter vps1 nc vps2 +5v comm c1 100pf c5 0.1f c3 100pf c2 100pf c4 0.1f lo rf in rf out 1 2 (2) 3 u2 c9 10f c10 10nf c11 22pf l1 15nh +5v +5v c12 22pf c101 (c7) 1.5pf c100 (c3) 0.5pf 1 3 4 2 c6 100pf c7 100pf r12 100? qp qn r7 100? in ip r fout dsop am p _out note: see adl5320 data sheet for component spacing () values 2 5 8 11 12 17 19 20 14 23 6 7 13 15 1 16 18 24 21 3 4 9 10 22 adl5320 10893-001 figure 1. circuit schematic for iq modulator with output power gain
cn-0283 circuit note rev. 0 | page 2 of 6 circuit description the ADL5375 is a general - purpose , high performance iq m odulator. it operates at output frequencies from 400 mhz to 6 ghz. because of its low noise and wide input baseband bandwidth (3 db) of 750 mhz, it can be driven by signals with a w ide variety of modulations and bandwidths. these input signals can be centered at dc or at a complex if. the lo interface to the ADL5375 is a 1xlo type, that is, the output frequency and lo frequency is equal (when the base - band signal is centered at dc ). circuit note cn - 0134 describes how th e adl5 375 can be driven by the adf4350 . system level calculations and rf amplifier choice in the 1 ghz to 2 ghz frequency range, the ADL5375 h as an output compression point (op1 db ) and a third - order compression point (oip3) of approximately 10 dbm and 25 dbm , respectively . in choosing an rf amplifier to provide gain after the iq m odulator , it is important to choose a device whose input p1db and input ip3 are equal or a little bit higher than these numbers . choosing a device with lower spec ification s result s in degraded performance for the cascade while choosing a device whose input p1db and input ip3 are significantly higher than those of the ADL5375 , has little benefit and is likely to needlessly increase the overall supply current of the signal chain. the adl5320 is a driv er amplifier (rf a mplifier that requires external tuning components) that is specified for operation from 400 mhz to 2700 mhz . it consumes 104 ma when operating from a 5 v supply (operation down to 3.3 v is possible with reduced pow er consumption and perfo rmance) . table 1 shows the output - referred ip3 (oip3) and p1db (op1db) of the ADL5375 iq m odulator along with the input - referred specifications of the adl5320 driver amplifier at 1900 mhz . in both cases, there is approximately a 3 db difference between the output - referred specifications of the iq m odulator and the input - referred spec ification s of the amplifier. table 1 . ip3 and p1db s pecifications for the ADL5375 iq modulator and the adl5320 driver amplifier at 1900 mhz parameter ADL5375 (output referred) adl5320 (input referred) ip3 24.2 dbm 28.3 dbm p1db 10 dbm 13 dbm figure 2 shows the simulated cascaded performance of the iq m odulat or and drive amplifier at 2140 mhz. this simulation was done using the adisimrf design tool . it is notable that the 12.3 db difference between the oip3 of the modulator (24.2 dbm) and the composite oip3 ( 36.5 dbm ) is just slightly less than the gain of the adl5320 driver amplifier , 13.7 db . this indicates that the driver amplifier has only a very slight effect on the overall oip3. 10893-002 figure 2. adisimrf design tool screen s hot showing cascaded performance of ADL5375 and adl5320
circuit note cn-0283 rev. 0 | page 3 of 6 figure 3 shows a plot of oip3 vs. output power (p out ) measured at the iq modulator output and at the output of the composite circuit . the shape of the two oip3 profiles are quite similar, just shifted in terms of output power and oip3. this reinforc es the idea that the ip3 is only slightly degrad ed as the signal passes through the rf amplifier 0 5 10 15 20 25 30 35 40 45 50 ?10 ?5 0 5 10 15 20 oip3 (dbm) composite output power (dbm) oip3 ADL5375 and adl5320 oip3 ADL5375 10893-003 figure 3. oip3 vs. p out at 2100 mhz for ADL5375 iq modulator and for the composite ci rcuit ( ADL5375 and adl5320 driver amplifier) choosing an output power level while the circuit achieves oip3 levels in the 35 dbm to 40 dbm range for output power levels up to 15 dbm, operation is not practical up to these levels , particularly with nonconstant envelope modulation schemes that tend to have relatively high peak - to - average ratios . to understand why , look at the volts - in to power - out transfer function o f the circuit and consider the typical drive levels that are available at the input to the iq modulator. figure 4 shows the transfer function of the circuit in terms of output power (in dbm) and input voltage (in v p- p) with a cw sine wave , drive signal . an iq m odulator , such as the ADL5375 , is driven typically by a dual , current - out , d igital - to -a nalog c onverter (dac) . normally, the two current outputs (0 ma to 20 ma nominal) of the d ac are terminated to ground with two 50 ? resistors and two 100 ? shunt resistors are placed across each of the i q inputs (for more information on this interface, see circuit note cn - 0205 ). with the dac running at 0 dbfs, this corresponds to a drive level at the iq m odulator of 1 v p-p or 0.353 v rms (this is neglecting the insertion loss of the low - pass filter that is generally placed between the dac and the iq m odu lator). this results in an output power of approximately 13 dbm. ?10 ?5 0 5 10 15 20 25 0.10 1 10 p out (dbm) v in (v p-p differential) p out ad l53 75 and ad l53 20 10893-004 figure 4. transfer function of circuit in t erms of output power in dbm and input level in v p- p d ifferential if it is assumed that the i and q inputs of the iq m odu lator are terminated with 100 ? as previously discussed , the output power relative to the dbfs drive level of a typical analog devices , inc., dac can be plotted (see figure 5 ). therefore, a drive level of 0 dbfs corresponds to 1 v p- p, resulting in the same 13 dbm output power previously discussed . ?10 ?5 0 5 10 15 20 ?20 ?15 ?10 ?5 0 p out (dbm) dbfs level (db) i and q inputs terminated with 100? i and q inputs unterminated 10893-005 figure 5 . transfer function of circuit in t erms of output power vs. dac drive level with iq modulator i and q inputs terminated with 100 ? and with i and q in puts unterminated figure 5 also shows the transfer function of the circuit when the i and q inputs are not terminated with 100 ? resistors. because the resulting dac v oltage drive level is doubled (2 v p- p max imum ), the resulting output power is higher by 6 db for the same dac drive level. while operation of the circuit without i and q termination resistors is possible, it does pose some problems for the filter that is usually placed between the dac and iq modulator. because this filter is generally terminated at both ends, it is desirable to have some resistance across the i and q inputs of the iq modulator (the unterminated input resistance of these inputs is approximately 60 k?). a value that is in the 100 ? to 1000 ? range can be used to increase the resulting dac voltage drive level and corresponding output power. however, take care to design
cn-0283 circuit note rev. 0 | page 4 of 6 the filter between the dac and iq modulator so that it can support different source and load impedances. as already noted, f rom figure 4 and figure 5 , it can be see n that a 1 v p- p sine wave (0 dbfs) is provide d an output power of approximately 13 d bm (the i and q inputs terminated with 100 ?) . in practice, the dac drive level must be reduced slightly from 0 dbfs to reduce distortion (typically 1 db to 2 db) . in addition to this, the rms drive level should be lower again by an amount equal to the peak - to - average ratio of the modulation of the carrier . the ratio of peak envelope power (pep) to rms p ower is typically in a range from 5 db for qpsk - like modulation schemes (0 db in the special case where the modulation is co nstant envelope) to around 1 0 db for higher order qam - based modulation . referring to figure 6 , this suggest s that output power levels in the 0 dbm to 10 dbm range are feasible . the adjacent channel power ratio (acpr) of a single carrier , wideband code division multiple access (wcdma) signal has becom e a popular metric for assessing the system level distortion of a circuit ( that is, as opposed to an assessment that is solely based on ip3 and imd levels ). figure 6 shows the measured acpr of the circuit vs. the o utput power level. in the case of a wcdma signal, acpr is defined as the ratio of the power in the carrier (in a bandwidth of 3.84 mhz) to the power in an adjacent channel (channel spacing = 5 mhz) , also measured in a 3.84 mhz bandwidth. the plot also show s an alternate channel power ratio that is the same type of measurement ; however, at a carrier offset of 10 mhz. ?92 ?90 ?88 ?86 ?84 ?82 ?80 ?78 ?76 ?74 ?72 ?70 ?68 ?66 ?64 ?62 ?60 ?58 ?56 ?54 ?52 ?50 ?8 ?6 ?4 ?2 0 2 4 6 8 10 adjacent and al tern a te channe l power r a tio (db) output power (dbm) adjacent channel power ratio (db) alternate channel power ratio (db) 10893-006 figure 6. plot of oip3 and wdcma acp r vs. output power in this case , the signal has a pep - to - rms ratio of approxima tely 10 db (the peak - to - average ratio of a wcdma signal can vary based on how the carrier is configured and loaded). based on this plot and the desired level of acpr, select an output power level in the 0 dbm to 10 dbm range. at power levels less than 0 db m, the acpr becomes dominated by the degrading signal- to - noise ratio of the circuit . common variations the adl5320 driver amplifier is specified to operate from 400 mhz to 2.7 ghz . this conveniently covers the lower end of the specified frequency range of the ADL5375 iq modulator. for operation at frequencies in the 2.3 ghz to 4 ghz range, the adl5321 driver amplifi er is recommended. both the adl5320 and adl5321 must be tuned to the frequency at which they will be operating. the data sheets of both devices contain tables tha t provide recommended values for tuning components at popular operating frequencies. a broadband internally matched gain block , such as the adl5601 or the adl5602 , can also be used to provide gain at the output of the iq m odulator. however, because these devices have lower oip3 (than adl5320 and adl5321 ) , they tend to dom inate and reduce the overall ip3 of the circuit. a number of narrow - band iq modulators are available that provide higher performance over their operating frequency ranges . examples are adl5370 / adl537 1 / adl537 2 / adl537 3 / adl537 4 . these narrow - band devices provide higher gain and o ip3 compared to ADL5375 . when paired with the adl5320 and adl5321 driver amplifiers, the net result is overall high er output power with similar composite oip3 . the adrf6701 / adrf670 2 / adrf670 3 / adrf670 4 famil ies of narrow - band iq m odulator s include an integrated phase - locked loop ( pll ) and voltage controlled oscillator ( vco ) . these device s provide similar performance to the adl5370 / adl5371 / adl5372 / adl5373 / adl5374 family ; however, with a higher level of i ntegration . a number of options exist to drive the i and q inputs of the iq modulator. the ad9125 and ad9122 are 16 - bit dual dacs that operate at 1 gsps or 1.2 gsps , respectively . these devices can be used to generate either a baseband spectrum (centered at 0 hz) or a c omplex if spectrum typically in the 100 mhz to 200 mhz range.
circuit note cn-0283 rev. 0 | page 5 of 6 circuit evaluation and t est the circuit was implemented using the ADL5375 evaluation board ( ADL5375 - 05 - e va l z ) that includes the adl5320 driver amplifier. this board can be configured to provide the iq modulator output signal, or the composite modulator and amplifier signal. the default configuration for this board is the modulator and amplifier composite output with the amplifier tuned for operation in the 1800 mhz to 2200 mhz range . as already noted, the adl5320 data sheet provides the values and placement locations for tuning capacitors that support other frequencies. equipment needed the following equipment is needed: ? the ADL5375 evaluation board ( ADL5375 -05- e va l z ) ? two rf signal generators : agilent 8648c or equivalen t operating at 25 mhz and 26 mhz ? a rf signal generator : agilent 8648c o r equivalent operating at approximately 2 ghz ? a rf spectrum analyzer : rohde & schwarz fsiq, rohde & schwarz fsq, agilent psa , or equivalent ? a zfsc -2-2- s+ 180 power splitter/combiner , mini - circuits ? a zmscq -2- 50+ 90 power splitter , mini - circuits ? two adt2 - 1t 1:2 b aluns , mini - circuits ? four zfbt - 6gw - ft+ bias tees , mini - circuits setup and test figure 7 shows the test setup that was used for the ip3 testing and for the power sweep testing. the signals from two rf sig nal generators running at 25 mhz and 26 mhz are passively combined using a 180 phase splitter/combiner that provides good input - to - input isolation. the 2 - tone signal is then applied to a 90 phase splitter that is specified to operate from 25 mhz to 50 mh z. these phase splitter outputs are then applied to two 1:2 transformers to create differential output signals (the 0 output of the phase splitter should go towards the ip and in inputs of the iq m odulator ). t he differential signals are applied to four bi as tees that bias the signals to 0.5 v. the network is terminated by two 100 ? resistors (pads for these resistors are provided on the ADL5375 evaluation board). the local oscillator (lo) for the ADL5375 is prov ided by a third signal generator, generating 0 dbm. the final output frequency is equal to the difference between the input rf signal frequencies and the lo frequency . therefore, if the 2 - tone signals are at 25 mhz and 26 mhz , and the lo is at 2150 mhz, the output spectrum appear s at 2124 mhz and 2125 mhz. the circuit can also be implemented using the ad9122 dual dac evaluation board ( ad9122-m5375- ebz ) that includes the ADL5375 iq m odulator. in this case, connect the output of the ADL5375 iq m odulator to a standalone adl5320 eva luation board ( adl5320 - e va l z ). the advantage of this approach is that the dac generates appropriately biased differential signals without the need for bias tees, phase splitters , and transformers. zmscq-2-50 90 power splitter adt2-1t 1:2 balun zfbt-6gw-ft+ bias tee +0.5v ADL5375-05 evaluation board (ADL5375-05-evalz) r7 ? r12 ? zfsc-2-2-s+ 180 power splitter/combiner adt2-1t 1:2 balun ibbp ibbn qbbp qbbn +5v vpos gnd amp_out zfbt-6gw-ft+ bias tee zfbt-6gw-ft+ bias tee zfbt-6gw-ft+ bias tee loip rf spectrum analyzer rf in rf sig gen 1 +8 dbm @ 25mhz rf sig gen 2 +8 dbm @ 26mhz rf sig gen 2 0 dbm @ 2150mhz 10893-007 figure 7. measurement setup for ip3 testing and power sweep
cn-0283 circuit note rev. 0 | page 6 of 6 learn more cn0283 design support package: http://www.analog.com/ cn0283 - designsupport n ash, eamon, correcting imperfections in iq modulators to impro ve rf signal fidelity , application note an - 1039, analog devices adisimrf des ign tool circuit note cn - 0016, interfacing the adl5370 i/q modulator to the ad9779a dual - channel, 1 gsps high speed dac , analog devices. circuit note cn - 0017, interfac ing the adl5371 i/q modulator to the ad9779a dual - channel, 1 gsps high speed dac , analog devices. circuit note cn - 0018, interfacing the adl5372 i/q modulator to the ad9779a dual - channel, 1 gsps high speed dac , analog devices. circuit note cn - 0019, interfacing the adl5373 i/q modulator to the ad9779a dual - channel, 1 gsps high speed dac , analog devices. circuit note cn - 0020, interfacing the adl5374 i/q modulator to the ad9779a dual - channel, 1 gsps high speed dac , analog devices. circuit note cn - 0021, interfacing the ADL5375 i/q modulator to the ad9779a dual - channel, 1 gsps high s peed dac , analog devices. circuit note cn - 0070, precise control of i/q modulator output power using the adl5386 quadrature modulator and the ad5621 12 - bit dac , analog devices. circuit note cn - 0134, broadband low error vector magnitude (evm) direct conversion transmitter , analog devices. circuit note cn - 0140, high performance, dual channel if sampling receiver , analog devices. circuit note cn - 0144, broadband low error vector magnitude (evm) direct conversion transmitter using lo divide - by - 2 modulator , analog devices. circuit note cn -0 205, interfacing the ADL5375 i/q modulator to the ad9122 dual channel, 1.2 gsps high speed dac , analog devices. circuit note cn - 0243, high dynamic range rf transmitter signa l chain using single external frequency reference for dac sample clock and iq modulator lo generation , analog devices. circuit note cn - 0245, wideband lo pll synthesizer with simple interface to quadrature demodulators , analog devices. data sheets and evaluation boards ADL5375 evaluation board, ADL5375 -05- e va l z adl5320 evaluation board, adl5320 - e va l z ad9122 evaluation board, ad9122 - m5375 - ebz ad l5375 data sheet ad l5320 data sheet revision history 9 /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 an alog devices or its licensors. while you may use the circuits from the l ab 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 fit ness 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 f rom 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. cn10893 -0- 9/12(0)
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