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lt5502 1 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. ieee802.11 high speed wireless lan wireless local loop single 1.8v to 5.25v supply if frequency range: 70mhz to 400mhz 84db limiting if gain 90db linear rssi range 7.7mhz lowpass output filter baseband i/q amplitude imbalance: <0.7db 4db noise figure low supply current: 25ma outputs biased up while in standby shutdown current: 1 m a 24-lead narrow ssop package applicatio s u features descriptio u typical applicatio u 400mhz quadrature if demodulator with rssi , ltc and lt are registered trademarks of linear technology corporation. the lt 5502 is a 70mhz to 400mhz monolithic integrated quadrature if demodulator. it consists of an if limiter,quadrature down mixers, integrated lowpass filters, and divide-by-two lo buffers. the demodulator provides all building blocks for demodulation of i and q baseband signals with a single supply voltage of 1.8v to 5.25v. the if limiter has 84db small-signal gain, and a built-in receive signal strength indicator (rssi) with over 90db linear range. the input referred noise-spectral-density is 1.45nv/ ? hz, which is equivalent to a 4db noise figure when the input is terminated with a 50 w source. the integrated lowpass output filters act as antialiasing andpulse-shaping filters for demodulated i/q-baseband sig- nals. the 3db cutoff frequency of the filters is about 7.7mhz. the vco frequency is required to be twice the desired operating frequency to provide quadrature local oscillator (lo) signals to the mixers. the standby mode provides fast transient response to the receive mode with reduced supply current when the i/q outputs are ac-coupled to a baseband chip. i/q output swing, rssi output vs if input power if input power (dbm) ?5 differential output swing (mv p-p ) 12001000 800600 400 200 rssi output (v) 1.21.0 0.8 0.6 0.4 0.2 ?0 ?5 ?0 ?5 5502 ta01b ?0 5 2xlo + 2xlo if + if en v cc i out + i out q out + q out 90 0 gnd 2v c21 f c11nf c41.8pf rssi enable 2xlo input if input r1240 c3 22nf basebanddifferential i/q outputs 5502 ta01a 2 lt5502 downloaded from: http:///
lt5502 2 power supply voltage ............................................ 5.5v lo input power .................................................. 10dbm if input power .................................................... 10dbm operating ambient temperature (note 2) ..............................40 c to 85 c storage temperature range ................. 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c voltage on any pin not to exceed ............................. v cc order part number t jmax = 150 c, ja = 85 c/w lt5502egn absolute axi u rati gs w ww u package/order i for atio uu w (note 1) electrical characteristics v cc = 3v, f 2xlo = 570mhz, p 2xlo = 10dbm, f if = 280mhz, p if = 50dbm, t a = 25 c, unless otherwise noted. (note 3) consult factory for parts specified with wider operating temperature ranges. 12 3 4 5 6 7 8 9 1011 12 top view gn package 24-lead narrow plastic ssop 2423 22 21 20 19 18 17 16 15 14 13 q out + q out v cc gndgnd 2xlo + 2xlo v cc v cc rssignd ift i out + i out gnd v cc gnd if + if gndgnd en stby ift + symbol parameter conditions min typ max units if input f if frequency range 70 to 400 mhz 3db limiting sensitivity 79 dbm noise figure terminated 50 source 4 db dc common mode voltage 2.6 v demodulator i/q output i/q output voltage swing differential 850 mv p-p i/q amplitude mismatch 0.1 0.7 db i/q phase mismatch 0.6 deg output driving capability differential; c max = 10pf 1.5 k dc common mode voltage 1.84 v rssi linear dynamic range (note 4) 3db linearity error 90 db output impedance 3.8 k output voltage input = 70dbm 0.27 0.41 0.54 v output voltage input = 0dbm 0.8 1.01 1.2 v output voltage slope input from 70dbm to 0dbm 8.7 mv/db linearity error input from 70dbm to 0dbm 1 db baseband lowpass filter 3db cutoff frequency 7.7 mhz group delay ripple 16.4 ns downloaded from: http:///
lt5502 3 typical perfor a ce characteristics uw power supply currentvs temperature i/q output swing vs temperature i/q output swing vs if input power electrical characteristics v cc = 3v, f 2xlo = 570mhz, p 2xlo = 10dbm, f if = 280mhz, p if = 50dbm, t a = 25 c, unless otherwise noted. (note 3) (note 3) if input power (dbm) ?5 differential output swing (mv p-p ) 5 5502 g03 ?0 ?5 ?0 ?5 ?0 12001000 800600 400 200 t a = 40 c t a = 25 c t a = 85 c v cc = 3v f if = 280mhz supply voltage (v) 1.8 supply current (ma) 5.5 5502 g01 2.5 3.5 4.5 3632 28 24 20 16 t a = 40 c t a = 25 c t a = 85 c supply voltage (v) 1.8 differential output swing (mv p-p ) 800 1000 5.5 5502 g02 600400 2.5 3.5 4.5 1200 t a = 40 c t a = 25 c t a = 85 c f if = 280mhz symbol parameter conditions min typ max units 2xlo f 2xlo frequency range 140 to 800 mhz p 2xlo input power 20 5 dbm dc common mode voltage 2.6 v power supply v cc supply voltage 1.8 5.25 v i cc supply current en = high 25 32 ma i off shutdown current en = low; standby = low 1 100 a standby mode current en = low; standby = high 2.6 3.5 ma note 1: absolute maximum ratings are those values beyond which the life a device may be impaired.note 2: specifications over the ?0 c to 85 c temperature range are assured by design, characterization and correlation with statistical processcontrols. note 3: tests are performed as shown in the configuration of figure 3. note 4: tests are performed as shown in the configuration of figure 1 for if input. downloaded from: http:///
lt5502 4 rssi output voltage vs v cc if input sensitivityvs temperature if input sensitivity vs if frequency typical perfor a ce characteristics uw lpf frequency responsevs baseband frequency lpf group delayvs baseband frequency lpf frequency response vs v cc (note 3) if input power (dbm) ?5 rssi output (v) 5 5502 g07 ?0 ?5 ?0 ?5 ?0 1.21.0 0.8 0.6 0.4 0.2 f if = 280mhz t a = 25 c v cc = 3v v cc = 5.5v v cc = 1.8v supply voltage (v) 1.8 input sensitivity (dbm) 5.5 5502 g08 2.5 3.5 4.5 ?3 ?5 ?7 ?9 ?1 ?3 t a = 40 c t a = 25 c t a = 85 c f if = 280mhz if frequency (mhz) 70 input sensitivity (dbm) ?9 ?6 5502 g09 ?2 ?5 150 200 250 300 350 400 100 ?3 t a = 40 c t a = 25 c v cc = 3v t a = 85 c baseband frequency (mhz) 0 gain response (db) 12 20 5502 g10 48 1 6 50 ? ?0?5 ?0 ?5 ?0 ?5 v cc = 3v t a = 85 c t a = 40 c t a = 25 c baseband frequency (mhz) 0 group delay (ns) 110 9580 65 50 35 20 4 8 12 16 5502 g11 20 v cc = 3v t a = 85 c t a = 40 c t a = 25 c baseband frequency (mhz) 0 gain response (db) 12 20 5502 g12 48 1 6 50 ? ?0?5 ?0 ?5 ?0 ?5 11090 70 50 30 v cc = 1.8v, 3v, 5.5v t a = 25 c group delay (ns) i/q output swing vs if input power rssi output vs temperature rssi output voltage vs if frequency if input power (dbm) ?5 differential output swing (mv p-p ) 5 5502 g04 ?0 ?5 ?0 ?5 ?0 12001000 800600 400 200 f if = 70mhz f if = 280mhz f if = 400mhz v cc = 3v t a = 25 c if input power (dbm) ?5 rssi output (v) 5 5502 g05 ?0 ?5 ?0 ?5 ?0 1.21.0 0.8 0.6 0.4 0.2 t a = 40 c t a = 85 c v cc = 3v f if = 280mhz t a = 25 c if input power (dbm) ?5 rssi output (v) 5 5502 g06 ?0 ?5 ?0 ?5 ?0 1.21.0 0.8 0.6 0.4 0.2 f if = 70mhz f if = 280mhz v cc = 3v t a = 25 c f if = 400mhz downloaded from: http:///
lt5502 5 uu u pi fu ctio s i out + (pin 1): positive baseband output pin of i-channel. the dc bias voltage is v cc ?1.16v. this pin should not be shorted to ground.i out (pin 2): negative baseband input pin of i-channel. the dc bias voltage is v cc ?1.16v. this pin should not be shorted to ground.gnd (pins 3, 5, 8, 9, 14, 20, 21): ground pin. v cc (pins 4, 16, 17, 22): power supply pin. this pin should be decoupled using 1000pf and 0.1 f capacitors. if + (pin 6): positive if input pin. the dc bias voltage is v cc ?0.4v. if (pin 7): negative if input pin. the dc bias voltage is v cc ?0.4v. en (pin 10): enable pin. when the input voltage is higher than 0.9v or up to v cc , the circuit is completely turned on. when the input voltage is less than 0.7v or down toground, the circuit is turned off except the part of the circuit associated with standby mode. stby (pin 11): standby pin. when the input voltage is higher than 0.9v or up to v cc , the circuit of standby mode is turned on to bias the i/q buffers to desired quiescent voltage. when the input voltage is less than 0.7v or downto ground, it is turned off. ift + (pin 12): interstage if positive pin. the dc bias voltage is v cc ?0.25v. ift (pin 13): interstage if negative pin. the dc bias voltage is v cc ?0.25v. rssi (pin 15): rssi output pin. 2xlo (pin 18): negative carrier input pin. the input- signal? frequency must be twice that of the desireddemodulator lo frequency. the dc bias voltage is v cc 0.4v.2xlo + (pin 19): positive carrier input pin. the input- signal? frequency must be twice that of the desireddemodulator lo frequency. the dc bias voltage is v cc 0.4v.q out (pin 23): negative baseband output pin of the q-channel. the dc bias voltage is v cc ?1.16v. this pin should not be shorted to ground.q out + (pin 24): positive baseband output pin of the q-channel. the dc bias voltage is v cc ?1.16v. this pin should not be shorted to ground. block diagra w 2xlo + 2xlo if + if en bias 5502 bd limiter 2 limiter 1 1 6 12 13 7 2 24 23 10 15 rssirssi lo buffers ift + ift i out + i out q out + q out q-mixer i-mixer lpf lpf 11 divide 2 0 /90 19 18 downloaded from: http:///
lt5502 6 applicatio s i for atio wu u u the lt5502 consists of the following sections: if limiter,i/q demodulators, quadrature lo carrier generator, inte- grated lowpass filters (lpfs), and bias circuitry. an if signal is fed to the inputs of the if limiter. the limited if signal is then demodulated into i/q baseband signals using the quadrature lo carriers that are generated from the divide-by-two circuit. the demodulated i/q signals are passed through 5th order lpfs and buffered with an output driver. if limiter the if limiter has 84db small-signal gain with a frequency range of 70mhz to 400mhz. it consists of two cascaded stages of if amplifiers/limiters. the differential outputs of the first stage are connected internally to the differential inputs of the second stage. an interstage filtering is possible in between (pin 12 and pin 13) with minimum off- chip components. it can be a simple parallel lc tank circuit l1 and c8 as shown in figure 3. the 22nf blocking capacitor, c19, is used for the proper operation of the internal dc offset canceling circuit. to achieve the best receiver sensitivity, a differential configuration at the if input is recommended due to its better immunity to 2xlo signal coupling to the if limiter. otherwise, the 2xlo interference, presented at the if inputs, may saturate the if limiter and reduce the gain of the wanted if signal. the receiver? 3db input-limiting sensitivity will be affected correspondingly. the interstage bandpass filter will mini- mize both 2xlo feedthrough and the receiver? noise bandwidth. therefore, the receiver? input sensitivity can be improved. without the interstage filter, the second stage will be limited by the broadband noise amplified by the first stage. the noise bandwidth in this case can be as high as 500mhz. the 3db input limiting sensitivity is about 79dbm at an if frequency of 280mhz when terminated with 200 at the input. the differential if input impedance is 2.2k . therefore, a 240 resistor is used for r3 as shown in figure 3. using a bandpass filter with 50mhz bandwidth, the input sensitivity is improved to 86dbm. the 1:4 if input transformer can also be replaced with anarrow band single-to-differential conversion circuit using three discreet elements as shown in figure 1. their nominal values are listed in table 1. due to the parasitics of the pcb, their values need to be compensated. the receiver? input sensitivity in this case is improved to 85dbm even without interstage filtering. the matching circuit is essentially a second order bandpass filter. there- fore, the requirement for the front-end channel-select filter can be eased too. figure 1. if input matching network at 280mhz table 1. the component values of matching networkl sh , c s1 and c s2 f if (mhz) l sh (nh) c s1 /c s2 (pf) 70 642 13.7 100 422 9.6 150 256 6.4 200 176 4.8 250 130 3.8 300 101 3.2 350 80.4 2.7 400 66.0 2.4 in an application where a lower input sensitivity is satisfac-tory, one of the if inputs can be simply ac-terminated with a 50 resistor and the other ac-grounded. the input receiver? sensitivity is about 76dbm at 280mhz in this case. c s1 3.3pf c5 22nf c s2 3.3pf l sh 120nh if input to if + to if 5502 f01 matching network downloaded from: http:///
lt5502 7 the receive signal strength indicator (rssi) is built intothe if limiter. the input if signal is detected in a current output proportional to the if input power. the current outputs from two cascaded stages of if amplifiers/limiters are summed and converted into the rssi voltage. the rssi output has an excellent linear range of 90db. the characteristic of rssi output voltage versus input if power is independent of temperature and process varia- tion. the nominal output impedance is 3.8k . an off-chip capacitor c7 is needed to reduce the rssi voltage ripple.its value can be determined using the following formula: c f f if 7 1 760 ? i/q demodulatorsthe quadrature demodulators are double balanced mix- ers, down converting the limited if signals from the if limiter into i/q baseband signals. the quadrature lo carriers are obtained from the internal quadrature lo carrier generator. the nominal output voltage of differen- tial i/q baseband signals is about 850mv p-p . these mag- nitudes are well matched, and their phases are 90 apart. quadrature lo carrier generatorthe quadrature lo carrier generator consists of a divide- by-two circuit and lo buffers. an input signal (2xlo) with twice the desired lo carrier frequency is used as the clock for the divide-by-two circuit, producing the quadrature lo carriers for the demodulators. the outputs are buffered and then drive the down converting mixers. with a full differential approach, the quadrature lo carriers are well matched. integrated low pass filters the 5th order integrated lowpass filters are used for filtering the down converted baseband outputs for both the i-channel and the q-channel. they serve as anti- aliasing and pulse-shaping filters. the i/q filters are well matched in gain response and group delay. the 3db corner frequency is 7.7mhz and the group delay ripple is 16.4ns. the i/q differential outputs have output driving capability of 1.5k with maximum capacitive loading of 10pf. the outputs are internally biased at v cc ?.16v. figure 2 shows the simplified output circuit schematic ofi-channel or q-channnel. applicatio s i for atio wu u u the i/q baseband outputs can be directly dc-coupled tothe inputs of a baseband chip. for ac-coupled applica- tions with large coupling capacitors, the stby pin can be used to prebias the outputs to the desired quiescent voltage at much reduced current. this mode only draws 2.6ma. when the en pin is then turned on, the chip is quickly switched to normal operating mode without long time constants due to charging or discharging the large coupling capacitors. table 2 shows the logic of the en pin and stby pin. in both normal operating mode and standby mode, the maximum discharging current is about 200 a, and the maximum charging current is more than 10ma.table 2. the logic of different operating modes en stby comments low low shutdown mode low high standby mode high low or high normal operation mode 5502 f02 200 a 200 a v cc i out + (or q out + ) i out (or q out ) i-channel (or q-channel): differential signals from lpf + + figure 2. simplified circuit schematicof i-channel (or q-channel) outputs downloaded from: http:///
lt5502 8 typical applicatio s u figure 3. evaluation circuit schematic with i/q output buffers + 12 3 4 5 6 7 8 9 1011 12 2423 22 21 20 19 18 17 16 15 14 13 q out + q out v cc gndgnd 2xlo + 2xlo v cc v cc rssi gnd ift i out + i out gndv cc gndif + if gndgnd en stby ift + 2 u1 lt5502 t1 jtx-4-10t 1:4 mini-circuit 4:1 mini-circuit if in r10 5.11k r7 49.9 r3 240 r2 20k r120k r9 51.1k c12 1.8pf r13 5.11k c16 1.8pf c5 22nf r4240 c10 1 f c11 f c91 f c2410 f c201 f c2510 f c21nf sw1 1 = en2 = stby 1 6 1 6 + 7 7 6 6 4 4 32 32 j2 i out i out + i out q out + q out q out j1 t2 jtx-4-10t j4 c231 f c19 22nf c11 1 f c41nf c3 1nf c181 f c71.8pf c13 1 f r16 49.9 j3 c17 1 f u2 lt1809cs u3 lt1809cs l1 c8 r17 if interstage optional circuit rssi v cc2 v cc1 v cc2 r6 2.55k c15 1 f r12 2.55k r8 51.1k r14 51.1k c14 1 f r1551.1k 2xlo 5502 f02 downloaded from: http:///
lt5502 9 typical applicatio s u figure 5. component side layout of evaluation board figure 4.component side silkscreen of evaluation board downloaded from: http:///
lt5502 10 typical applicatio s u figure 7. bottom side layout of evaluation board figure 6.bottom side silkscreen of evaluation board downloaded from: http:///
lt5502 11 package descriptio u dimensions in inches (millimeters) unless otherwise noted. 0.337 ?0.344* (8.560 ?8.738) gn24 (ssop) 1098 * dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side ** dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side 12 3 4 5 6 7 8 9 10 11 12 0.229 ?0.244 (5.817 ?6.198) 0.150 ?0.157** (3.810 ?3.988) 1617 18 19 20 21 22 23 24 15 14 13 0.016 ?0.050 (0.406 ?1.270) 0.015 0.004 (0.38 0.10) 45 0 ?8 typ 0.007 ?0.0098 (0.178 ?0.249) 0.053 ?0.068 (1.351 ?1.727) 0.008 ?0.012 (0.203 ?0.305) 0.004 ?0.0098 (0.102 ?0.249) 0.0250 (0.635) bsc 0.033 (0.838) ref gn package 24-lead plastic ssop (narrow 0.150) (ltc dwg # 05-08-1641) downloaded from: http:///
lt5502 12 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear-tech.com ? linear technology corporation 2001 5502f lt/tp 0101 2k ? printed in usa typical applicatio u example: 2.4ghz to 2.5ghz receiver application (rx if = 280mhz) 5502 ta02 lo buffer f/2 i mixer q mixer i outputs q outputs 12 24 23 1110 a/d a/d baseband processor bufferbuffer lpf lpf 0 90 limiter 1 limiter 2 stby en lt5502 30nh 30nh 200 2.7pf 100pf 2.7pf if synthesizer 3,5,8,9,14,20,21 18 19 1.8pf 15 120nh 22nf 3.3pf 4,16,17,22 v cc 0.1 f 2v 12 13 6 7 280mhz if saw bp filter rx front end rx input: 2.4ghz to 2.5ghz main synthesizer 3.3pf rssi 2nd lo, 560mhz 1st lo,2.12ghz to 2.22ghz 1nf 1nf downloaded from: http:///

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