general description the max2685? low-noise amplifier (lna) and down- converter mixer comprise the major blocks of an rf front-end receiver. optimized for 900mhz operation, the device? low noise figure, high gain, and high linear- ity make it ideal for cellular, cordless, and wireless data applications. a low supply current of 8.5ma (high-gain mode) and 3.8ma (low-gain mode) plus a low operating supply voltage range of +2.7v to +5.5v make it suitable for use in 3-cell nicd or 1-cell lithium-ion (li+) battery applications. a low-power shutdown mode further extends battery life by reducing supply current below 0.1?. the max2685 includes an lna, lna bypass switch, downconverter mixer, and local-oscillator (lo) buffer. the lna has a low noise figure of 1.4db, a high gain of 15db, and an input third-order intercept point (ip3) of -4dbm. the mixer has a noise figure of 13db, a gain of 6db, and an input ip3 of +7dbm. in addition, an lna bypass switch allows two levels of gain, reducing power consumption when high gain is not needed. the downconverter mixer has a single-ended rf input port and differential if output ports. differential opera- tion of the if ports offers improved even-order harmonic rejection and increased immunity to noise. an lo buffer allows the lo port to be driven with only -8dbm of lo power. the max2685 is offered in a space-saving 16- pin qsop package. applications cellular/cordless phones 900mhz ism-band radios wireless data 868mhz european ism band features 800mhz to 1000mhz rf frequency range +2.7v to +5.5v single-supply operation integrated lna + mixer + lo buffer logic-controlled lna bypass switch reduces supply current lna performance (high/low gain) gain: +15db/-12db nf: 1.4db/12db input ip3: -4dbm/+16dbm mixer performance (high/low gain) gain: 6db/4.6db nf: 13db/12db input ip3: +7dbm/-1.5dbm supply current 8.5ma (high gain) 3.8ma (low gain) <0.1? supply current in shutdown mode 0.8? receiver enable time max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer ________________________________________________________________ maxim integrated products 1 v cc ifout+ ifout- max2685 lnain gain lna lo lnaout mixin lna bypass lo buffer mixer shdn power management gnd 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 lnaout gnd v cc v cc mixin gnd gnd ifout+ ifout- top view max2685 qsop lnain shdn gain gnd gnd lo gnd functional diagram 19-1493; rev 1; 12/00 part max2685eee -40? to +85? temp. range pin-package 16 qsop evaluation kit available pin configuration ordering information for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer 2 _______________________________________________________________________________________ absolute maximum ratings dc electrical characteristics (v cc = +2.7v to +5.5v, v shdn = +2v, v gain = +2v, lnain = lnaout = mixin = lo = unconnected, ifout+ = ifout- = v cc , t a = -40? to +85?. typical values are at t a = +25? and v cc = +3v, unless otherwise noted.) ac electrical characteristics (max2685 ev kit, v cc = v shdn = +3v, f lnain = f mixin = 880mhz, f lo = 960mhz, p lnain = -30dbm, p lo = -8dbm, p mixin = -25dbm, differential ifout operation, z o = 50 ? , t a = +25?, unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v cc to gnd ..............................................................-0.3v to +6v lnain input power (50 ? source)...................................+10dbm lo input power (50 ? source) ........................................+10dbm mixin input power (50 ? source) ...................................+10dbm ifout+, ifout- to gnd ..........................................-0.3v to +6v lnaout to gnd ......................................................-0.3v to +6v gain, shdn to gnd..................................-0.3v to (v cc + 0.3v) continuous power dissipation (t a = +70?) 16-pin qsop (derate 8.3mw/? above +70?)............667mw junction temperature ......................................................+150? operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? shdn = gnd (note 1) gain = v cc (note 1) gain, shdn gain, shdn v shdn = v gain = 0 to 5.5v (note 1) conditions ? 0.1 1.0 shutdown supply current 8.5 14.1 v 2.7 5.5 supply voltage range v 2.0 logic input voltage high v 0.5 logic input voltage low ? ?.01 ? logic input current units min typ max parameter gain = gnd (note 1) ma 3.8 6.4 operating supply current gain = gnd (note 1) db -14 -12 -10.3 gain = v cc , t a = t min to t max (note 3) lna gain gain = v cc (note 1) gain = v cc gain = gnd gain = v cc conditions db 0.9 1.6 lna gain variation over temperature 13 15 16.2 1.4 db 12.2 lna noise figure -18.4 lna input 1db compression units min typ max parameter mhz 800 1000 rf frequency range (note 2) gain = v cc gain = gnd dbm -18.6 db -11.3 lnaout port return loss mhz 800 1000 rf frequency range (note 2) gain = gnd (note 1) db 2.5 4.6 6.0 mixer conversion gain gain = v cc (note 1) 4.7 6.1 7.0 gain = v cc (note 4) gain = gnd (note 5) -4.1 dbm +16.2 lna input ip3 low-noise amplifier (lna) downconverter mixer
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer _______________________________________________________________________________________ 3 ac electrical characteristics (continued) (max2685 ev kit, v cc = v shdn = +3v, f lnain = f mixin = 880mhz, f lo = 960mhz, p lnain = -30dbm, p lo = -8dbm, p mixin = -25dbm, differential ifout operation, z o = 50 ? , t a = +25?, unless otherwise noted.) note 1: performance at temperatures greater than or equal to +25? are guaranteed by production test; performance at tempera- tures less than +25? are guaranteed by design and characterization. note 2: this is the recommended operating frequency range. note 3: maximum and minimum limits are guaranteed by design and device characterization and are not production tested. note 4: two tones at 880mhz and 880.1mhz, -30dbm per tone. note 5: two tones at 880mhz and 880.1mhz, -10dbm per tone. note 6: two tones at 880mhz and 880.1mhz, -25dbm per tone. note 7: time from shdn = high, until the cascaded receive gain is within 1db of its final value. measured with 47pf blocking capacitors on lnain and lnaout. matching network removed from ifout output. typical operating characteristics (max2685 ev kit, v cc = v shdn = +3v, f lnain = f mixin = 880mhz, f lo = 960mhz, p lnain = -30dbm, p lo = -8dbm, p mixin = -25dbm, differential ifout operation, z o = 50 ? , t a = +25?, unless otherwise noted.) 0 3 2 1 4 5 6 7 8 9 10 2.5 3.5 3.0 4.0 4.5 5.0 5.5 supply current vs. supply voltage max2685 toc01 supply voltage (v) supply current (ma) gain = high gain = low t a = +85? t a = +25? t a = -40? t a = +85? t a = +25? t a = -40? 0 3 2 1 4 5 6 7 8 9 10 2.5 3.5 3.0 4.0 4.5 5.0 5.5 shutdown supply current vs. supply voltage max2685 toc02 supply voltage (v) shutdown supply current (na) shdn = gnd t a = -40 c t a = +25 c t a = +85 c -15 -5 -10 5 0 15 10 20 2.5 3.5 4.0 3.0 4.5 5.0 5.5 lna gain vs. supply voltage max2685 toc03 supply voltage (v) gain (db) gain = high gain = low t a = +85 c t a = +25 c t a = -40 c t a = +85 c t a = +25 c t a = -40 c gain = gnd db 12.1 mixer noise figure (ssb) gain = v cc , t a = t min to t max (note 3) gain = v cc db 12 mixer conversion gain variation over temperature (note 7) db gain = v cc gain = gnd conditions ? 0.8 receiver enable time 13 7 dbm -1.5 mixer input ip3 (note 6) 11 lo port return loss units min typ max parameter db shdn = v cc or gnd 53 lo-to-lnain isolation db db 28 lnaout-to-mixin isolation 31 lo-to-mixin isolation overall system
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer 4 _______________________________________________________________________________________ typical operating characteristics (continued) (max2685 ev kit, v cc = v shdn = +3v, f lnain = f mixin = 880mhz, f lo = 960mhz, p lnain = -30dbm, p lo = -8dbm, p mixin = -25dbm, differential ifout operation, z o = 50 ? , t a = +25?, unless otherwise noted.) -10 0 -5 10 5 15 20 2.5 3.5 4.0 3.0 4.5 5.0 5.5 lna input ip3 vs. supply voltage max2685 toc04 supply voltage (v) input ip3 (dbm) gain = high gain = low t a = +85 c t a = +25 c t a = -40 c t a = +85 c t a = +25 c t a = -40 c -20 -10 -15 0 -5 5 10 15 20 800 850 875 825 900 925 950 975 1000 lna gain vs. frequency max2685 toc05 frequency (mhz) gain (db) gain = high gain = low 1.0 1.2 1.1 1.4 1.3 1.6 1.5 1.7 1.9 1.8 2.0 870 890 900 910 880 920 930 940 950 960 lna noise figure vs. frequency max2685 toc06 frequency (mhz) noise figure (db) -40 -30 -35 -20 -25 -15 -10 -5 0 800 850 875 825 900 925 950 975 1000 lna reverse isolation vs. frequency max2685 toc07 frequency (mhz) reverse isolation (db) gain = high gain = low lna s11 vs. frequency (800mhz to 1000mhz unmatched) max2685 toc10 gain = high gain = low 800 1000 800 hi lo 1000 -15 -12 -13 -14 -11 -10 -9 -8 -7 -6 -5 800 880 840 920 960 1000 lna input return loss vs. frequency max2685 toc08 frequency (mhz) input return loss (db) gain = high gain = low -20 -14 -16 -18 -12 -10 -8 -6 -4 -2 0 800 880 840 920 960 1000 lna output return loss vs. frequency max2685 toc09 frequency (mhz) output return loss (db) gain = high gain = low 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 2.5 3.5 3.0 4.0 4.5 5.0 5.5 mixer gain vs. supply voltage max2685 toc11 supply voltage (v) gain (db) t a = -40 c t a = +85 c t a = +85 c t a = +25 c t a = +25 c t a = -40 c gain = high gain = low -10 -4 -6 -8 -2 0 2 4 6 8 10 2.5 3.5 3.0 4.0 4.5 5.0 5.5 mixer input ip3 vs. supply voltage max2685 toc12 supply voltage (v) input ip3 (dbm) gain = high gain = low t a = +85 c t a = +25 c t a = -40 c t a = +85 c t a = +25 c t a = -40 c
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer _______________________________________________________________________________________ 5 typical operating characteristics (continued) (max2685 ev kit, v cc = v shdn = +3v, f lnain = f mixin = 880mhz, f lo = 960mhz, p lnain = -30dbm, p lo = -8dbm, p mixin = -25dbm, differential ifout operation, z o = 50 ? , t a = +25?, unless otherwise noted.) -12 -6 -8 -10 -4 -2 0 2 4 6 8 60 70 80 90 100 mixer gain vs. if frequency max2685 toc13 if frequency (mhz) gain (db) bandwidth determined by differential-to-single-ended converter circuit gain = high gain = low 0 2 1 4 3 6 5 7 -15 -10 -5 0 mixer gain vs. lo power max2685 toc14 lo power (dbm) gain (db) gain = high gain = low 10.0 11.5 11.0 10.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 -15 -10 -5 0 mixer noise figure vs. lo power max2685 toc15 lo power (dbm) noise figure (db) gain = high gain = low -15 -12 -13 -14 -10 -11 -6 -7 -8 -9 -5 750 800 850 900 950 1000 1050 1100 lo port return loss vs. frequency max2685 toc16 frequency (mhz) return loss (db)
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer 6 _______________________________________________________________________________________ pin description name function 1, 3, 8, 11, 12, 14 gnd ground. connect to ground plane with a low-inductance connection. 2 lnain rf input to lna and lna bypass switch. requires an external matching network and a series dc-blocking capacitor. pin 4 gain gain control logic-level input. drive high to enable the lna, open the lna bypass switch, and increase the receiver? gain. drive low to disable the lna, close the lna bypass switch, and reduce the receiver? gain. 5, 15 v cc supply voltage. bypass v cc to gnd at each pin with a 47pf capacitor as close to the pin as possible. 6 shdn shutdown control logic-level input. drive high or connect to v cc for normal operation. drive low to place the device in low-power shutdown mode. 7 lo local-oscillator input to downconverter mixer. requires a series dc-blocking capacitor and an imped- ance-setting resistor (typically 75 ? to ground). 9 ifout- inverting side to downconverter mixer? differential open-collector if output. requires a pull-up induc- tor to v cc for proper biasing, as well as a matching network to ensure optimum output power. 10 ifout+ noninverting side of downconverter mixer? differential open-collector if output. requires a pull-up inductor to v cc for proper biasing, as well as a matching network to ensure optimum output power. 13 mixin rf input to downconverter mixer. requires an external matching network and series dc-blocking capacitor. 16 lnaout lna output. internally matched to 50 ? . lnaout has an internal blocking capacitor. lna input 880mhz max2685 6pf 6pf 3.3pf 300pf 300pf lna output mixer input 880mhz 47pf 12pf if output 80mhz 1 2 3 4 5 0.1 f 12nh 6 7 330pf 75 ? 8 12 13 14 15 16 11 10 9 gnd lnaout mixin gnd *optional for broadband match. r* ifout- ifout+ 680nh 820nh lo lnain v cc v cc v cc v cc 47pf gain v cc shdn gnd gnd gnd gnd gain- control input shutdown input 1000pf lo input 960mhz figure 1. typical operating circuit
detailed description the max2685 consists of five major components: a low-noise amplifier (lna), an lna bypass switch, a downconverter mixer, a local-oscillator (lo) buffer, and a power-management block. low-noise amplifier (lna) the lna is a wideband, single-ended cascode amplifi- er that operates over a wide range of frequencies. the input of the lna (lnain) requires an appropriate matching network and a dc-blocking capacitor. the typical operating circuit shown in figure 1 is optimized for frequencies around 880mhz, requiring only a 0.1? capacitor in series with a 12nh inductor. see table 1 for the lna ??parameters for matching to other fre- quencies. the output of the lna (lnaout) is internally biased to v cc . it is internally matched to 50 ? and incorporates an internal dc-blocking capacitor. lna bypass switch and gain control when a large input signal is present, enable the lna bypass function to increase linearity and reduce supply current. set gain low to enable the lna bypass func- tion. receive mixer the downconverter mixer is a wideband, single-bal- anced design with a low noise figure and high linearity. the rf signal at the mixin port is mixed with the signal at the lo port, and is downconverted to an if frequen- cy at the differential if port. rf input the mixin input requires a simple external matching network and a series dc-blocking capacitor. see figure 1 for a matching network example, optimized for 880mhz operation. table 2 lists mixer ??parameters for matching to other frequencies. max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer _______________________________________________________________________________________ 7 table 1. lna typical s-parameters (v cc = +3v, t a = +25?) | s11 | mag frequency (mhz) 800 0.761 s11 phase (degrees) -64.5 | s21 | mag s21 phase (degrees) 177.9 4.98 | s12 | mag s12 phase (degrees) -163.7 | s22 | mag s22 phase (degrees) -107.3 0.376 0.018 -68.6 167.2 5.06 -167.1 840 0.753 -107.0 0.264 0.022 -73.2 156.6 5.07 -171.3 880 0.747 -94.6 0.172 0.026 -78.0 146.6 4.91 -175.7 920 0.733 -62.9 0.149 0.030 -82.8 137.7 4.68 178.0 960 0.719 -42.4 0.200 0.035 -87.5 130.3 4.40 171.0 1000 0.693 -38.8 0.263 0.039 -45.6 73.0 0.188 71.9 800 0.625 -91.3 0.483 0.191 -48.1 65.5 0.195 64.2 840 0.621 -91.3 0.423 0.198 -50.9 58.1 0.199 56.7 880 0.619 -89.9 0.370 0.201 -53.3 51.6 0.200 50.3 920 0.611 -86.1 0.337 0.202 -55.5 46.1 0.200 44.7 960 0.608 -80.9 0.322 0.201 -57.5 41.2 0.200 40.0 1000 0.607 -76.7 0.317 0.200 high-gain mode (gain = v cc ) low-gain mode (gain = gnd)
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer 8 _______________________________________________________________________________________ table 2. mixer typical s-parameters (v cc = +3v, t a = +25?) s11 mag | s11 | phase (degrees) 152.7 | s22 | mag (ifout+ port only) s22 phase (ifout+ port only) (degrees) -0.4 if frequency (mhz) 10 rf frequency (mhz) 0.996 -1.8 40 800 0.355 0.994 -3.2 80 0.993 153.7 -4.2 110 0.989 840 0.352 -6.2 170 0.988 154.5 -8.0 240 0.983 880 0.351 155.8 920 0.349 156.2 960 0.352 156.9 1000 0.353 142.8 -0.5 10 0.996 -1.8 40 800 0.275 0.995 -3.2 80 0.993 144.1 -4.2 110 0.989 840 0.268 -6.2 170 0.987 145.5 -7.9 240 0.982 880 0.262 147.7 920 0.255 149.0 960 0.254 156.9 1000 0.245 high-gain mode (gain = v cc ) low-gain mode (gain = gnd)
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer _______________________________________________________________________________________ 9 local-oscillator input the lo port is the high-impedance input of the local- oscillator buffer. it requires a series dc-blocking capacitor and a shunt resistor to ground to set the input impedance. see the typical operating characteristics for a graph of lo port return loss vs. frequency. if output port the mixer? downconverted output appears on the dif- ferential ifout+ and ifout- pins. the differential out- put can be converted to a single-ended output, as shown in the max2685 evaluation kit (ev kit). refer to the detailed description in the max2685 ev kit data sheet. shutdown drive shdn low to disable all device functions and place the max2685 in low-power shutdown mode. drive shdn high or connect it to v cc to enable all device functions. applications information layout considerations a properly designed pc board is an essential part of any rf/microwave circuit. note the ic? high-frequency inputs and outputs, and be sure to decouple the dc supply and control pins. for power-supply traces and connections, a star topol- ogy works well. each v cc node in the circuit has its own path to the central v cc node and a decoupling capacitor that provides a low impedance at the rf fre- quency of interest. the central v cc also has a large decoupling capacitor. this provides good isolation between the different sections of the max2685. chip information transistor count: 295
max2685 low-cost, 900mhz, low-noise amplifier and downconverter mixer package information qsop.eps maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2000 maxim integrated products printed usa is a registered trademark of maxim integrated products.
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