19-2301; Rev 0A; 6/02 KIT ATION EVALU E L B A IL AVA LNAs with Step Attenuator and VGA The MAX2371/MAX2373 can work over the frequency range from 100MHz to 1GHz. In practice, only a narrow band is needed in each application, so different matching circuits can be applied. The devices are dynamically configured through the digital/analog control pins to select either maximum gain and low noise figure or power-saving mode. In addition, the MAX2371/MAX2373 feature high/low-current modes, high/low attenuation modes, linearly controlled gain states, and shutdown mode. Features ♦ Low Noise Figure (1.8dB typical) ♦ High Small-Signal Gain (15dB Nominal) ♦ Wide Frequency Range of Operation (100MHz to 1GHz) ♦ 20dB Step Attenuator ♦ 45dB AGC Range Excluding Step Attenuator ♦ 2.65V to 3.3V Single-Supply Operation ♦ Shutdown Mode ♦ 3.5mA Supply Current, Adjustable Down to 2.5mA ♦ 40dB Reverse Isolation Applications Ordering Information Direct Conversion Receiver (DCR) PART Very Low IF Receiver TEMP RANGE PIN-PACKAGE MAX2371EGC -40°C to +85°C 12 QFN MAX2373EGC -40°C to +85°C 12 QFN GND RF_VCC RSET Pin Configuration 12 11 10 TOP VIEW 2 RX_EN 3 MAX2371 MAX2373 4 5 6 LNA_I LNA_E AGC 1 RF_ATTN LNA_IN Functional Diagram GND RSET RF_VCC AGC_BYP MAX2371 MAX2373 LNA_IN 9 AGC_BYP 8 LNA_VCC 7 LNA_OUT LNA_E RF ATTENUATOR RX_EN LNA LNA_VCC AGC AMP LNA_OUT EXPONENTIAL CONVERTER RF_ATTN AGC LNA_I ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX2371/MAX2373 General Description The MAX2371/MAX2373 wideband low-noise amplifier (LNA) ICs are designed for direct conversion receiver (DCR) or very low intermediate frequency (VLIF) receiver applications. They contain single-channel, single-ended LNAs with switchable attenuator and automatic gain control (AGC) intended as a low-noise gain stage. These devices provide high gain-control range (typically 60dB) at radio frequency (RF) with excellent noise and reverse isolation characteristics. MAX2371/MAX2373 LNAs with Step Attenuator and VGA ABSOLUTE MAXIMUM RATINGS VCC to GND ...........................................................-0.3V to +3.6V All Pins Excluding Grounds to Pin GND.....-0.3V to (VCC + 0.3V) LNA Input Power (RX_EN = low) ........................................5dBm Continuous Power Dissipation (TA = +70°C) 12-Pin QFN (derate 11.9mW/°C above +70°C) ...........952mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +160°C Soldering Temperature (10s) ...........................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. DC ELECTRICAL CHARACTERISTICS (VCC = 2.775V, RX_EN = high, RSET = 1.1kΩ, VAGC = VCC/2, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER Supply Voltage SYMBOL CONDITIONS VCC MIN TYP MAX 2.65 UNITS 2.775 3.30 V RX_EN = low, VCC = 3.3V 0.5 20 µA LNA_I = high, RF_ATTN = low 3.5 5.5 mA 3.5 mA VCC V Supply Current ICC Digital Input Logic High VIH Pins LNA_I, RF_ATTN, RX_EN Digital Input Logic Low VIL Pins LNA_I, RF_ATTN, RX_EN LNA_I = low 2.5 0.7 ✕ VCC 0.3 ✕ VCC 0 V Logic Pin Impedance Logic pins RX_EN, RF_ATTN, LNA_I 50 kΩ AGC Pin Impedance Pins AGC 100 kΩ AC ELECTRICAL CHARACTERISTICS (MAX2371/MAX2373 EV Kits, VCC = 2.65V to 3.3V, RX_EN = high, RSET = 1.1kΩ, TA = -40°C to +85°C. Typical values are at VCC = 2.775V; for MAX2371 fRF = 150MHz, for MAX2373 fRF = 850MHz to 940MHz; TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS LNA AND AGC AMP CHARACTERISTICS Radio Frequency Range (Note 2) Input Return Loss (S11) (Note 3) Reverse Isolation (S12) Max Power Gain (Note 3) Low band (MAX2371) 136 150 174 High band (MAX2373) 850 900 940 LNA_I = high; RF_ATTN = low MAX2371 -12 -9.5 MAX2373 -15 -9.5 LNA_I = high; RF_ATTN = high MAX2371 -14 -10 MAX2373 -10 -6.5 Over AGC range LNA_I = high, TA = +25°C, VCC = 2.775V LNA_I = low, TA = +25°C, VCC = 2.775V Gain Variation Over Temperature 2 MAX2371 -40 -35 MAX2373 -42 -35 13 14.5 16 MAX2373 14 15.5 17 MAX2371 10.5 12 MAX2373 10.5 13 MAX2371 TA = -40°C to +85°C, VAGC < 1.8V -2.0 _______________________________________________________________________________________ 2.0 MHz dB dB dB dB LNAs with Step Attenuator and VGA (MAX2371/MAX2373 EV Kits, VCC = 2.65V to 3.3V, RX_EN = high, RSET = 1.1kΩ, TA = -40°C to +85°C. Typical values are at VCC = 2.775V; for MAX2371 fRF = 150MHz, for MAX2373 fRF = 850MHz to 940MHz; TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS LNA_I = high, TA = +25°C, VCC = 2.775V, RF_ATTN = low SSB Noise Figure vs. AGC LNA_I = low, TA = +25°C, VCC = 2.775V, RF_ATTN = low Input 1dB Compression Point RF_ATTN = low, VAGC < 1.8V RF_ATTN = high, VAGC < 1.8V RF_ATTN = low, VAGC = VCC/2 Input IP3 (Notes 4, 5) RF_ATTN = high, VAGC = VCC/2 to 2.575V Input IP3 Over AGC Range MIN TYP MAX VAGC = 1.275V 1.8 2.2 VAGC = 1.575V 5.0 7.7 VAGC = 1.875V 11 14.5 VAGC = 2.175V 20 VAGC = 1.275V 2.1 LNA_I = high -21.5 19.5 LNA_I = low -24 -22 LNA_I = high -3 0 LNA_I = low -9 -6.5 LNA_I = high -5 -1 LNA_I = low MAX2371 -7 -4 MAX2373 -12 -9 9 13 LNA_I = high dB 2.6 dBm dBm dBm MAX2371 -10.5 -8 MAX2373 -12.5 -10.5 VCC = 2.775V, RF_ATTN = low, VAGC = 1.3375V to 2.575V, TA = +25°C 35 45 RF_ATTN = low, VAGC = 1.625V 32 40 47 RF_ATTN = high, VAGC = 1.625V 24 33 41 MAX2371 16.0 17.5 19.0 MAX2373 18.0 19.5 21.0 RF_ATTN = low, LNA_I = high, VAGC = VCC/2 to 1.80V UNITS dBm AGC RESPONSE AGC Attenuation Range (Note 6) AGC Slope Over Control Range dB dB/V RF STEP ATTENUATOR Gain Step Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: RF_ATTN = high to low, LNA_I = high dB Parameters over temperature and supply voltage range are guaranteed by design and characterization, unless otherwise noted. Operation outside these frequency bands is possible but has not been characterized. See Typical Operating Characteristics. Measured with external matching network. fIN1 = 150MHz, fIN2 = 150.1MHz, PIN = -30dBm for both tones (MAX2371). fIN1 = 900MHz, fIN2 = 900.1MHz, PIN = -30dBm for both tones (MAX2373). Parameters are guaranteed by production test. _______________________________________________________________________________________ 3 MAX2371/MAX2373 AC ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (MAX2371/MAX2373 EV Kits, VCC = 2.775V, RX_EN = high, RSET = 1.1kΩ, LNA_I = high, TA = +25°C. For MAX2371, fRF = 150MHz; for MAX2373, fRF = 900MHz, unless otherwise noted.) MAX2371 GAIN vs. VAGC RF_ATTN = LOW 10 TA = -40°C 15 -10 10 -20 TA = +85°C -30 0 RF_ATTN = HIGH -10 RF_ATTN = HIGH RF_ATTN = LOW -60 150 160 170 1.2 180 1.6 2.0 P1dB vs. VAGC TA = +85°C -10.0 25 -15.0 20 15 10 -20.0 5 -25.0 0 1.7 2.2 -10 -15 -20 S11 -25 RF_ATTN = LOW -30 1.7 VAGC (V) -40 2.2 S12 130 2.7 VAGC (V) 140 150 S11, S22, S12 vs. VAGC MAX2371 toc07 S11 S11, S22, S12 (dB) -10 S22 S11 RF_ATTN = LOW -30 RF_ATTN = HIGH -40 -50 S12 -60 1.2 1.7 2.2 2.7 VAGC (V) 4 160 FREQUENCY (MHz) 0 -20 RF_ATTN = HIGH -50 1.2 2.7 S22 -5 -45 1.2 1.8 -35 RF_ATTN = LOW RF_ATTN = LOW 1.7 0 S11, S22, S12 (dB) TA = +25°C 1.6 S11, S22, S12 vs. FREQUENCY RF_ATTN = HIGH NOSIE FIGURE (dB) 0 TA = -40°C 1.5 VAGC (V) 30 MAX2371 toc04 RF_ATTN = HIGH -5.0 1.4 1.3 NOISE FIGURE vs. VAGC 10.0 5.0 2.8 2.4 VAGC (V) FREQUENCY (MHz) MAX2371 toc06 140 -15 MAX2371 toc05 130 TA = -40°C -5 TA = -40°C -50 -10 TA = +25°C TA = +85°C 5 0 TA = +25°C -40 -5 RF_ATTN = HIGH 20 0 IIP3 (dBm) TA = +85°C TA = +25°C 5 GAIN (dB) GAIN (dB) 10 25 MAX2371 toc02 MAX2371 toc01 RF_ATTN = LOW 15 IIP3 vs. VAGC 20 MAX2371 toc03 GAIN vs. FREQUENCY 20 P1dB (dBm) MAX2371/MAX2373 LNAs with Step Attenuator and VGA _______________________________________________________________________________________ 170 180 LNAs with Step Attenuator and VGA MAX2373 RF_ATTN = LOW 10 RF_ATTN = HIGH 15 10 TA = +85°C 0 -10 -20 TA = -40°C TA = +25°C -30 -5 -10 RF_ATTN = LOW -15 -50 860 880 900 920 940 1.2 1.6 2.0 FREQUENCY (MHz) P1dB vs. VAGC 1.5 TA = 85°C -10.0 -15.0 RF_ATTN = LOW 15 RF_ATTN = LOW 10 1.8 S11 -5 -10 -15 S22 -20 -25 S11 RF_ATTN = LOW -30 RF_ATTN = HIGH -35 -40 5 -20.0 1.7 0 MAX2371 toc12 RF_ATTN = HIGH 20 1.6 S11, S22, S12 vs. FREQUENCY 25 NOSIE FIGURE (dB) 0 TA = -40°C TA = +25°C 1.4 VAGC (V) 30 MAX2371 toc11 RF_ATTN = HIGH -5.0 1.3 2.8 NOISE FIGURE vs. VAGC 10.0 5.0 2.4 VAGC (V) S11, S22, S12 (dB) 840 0 RF_ATTN = HIGH -10 TA = +85°C -5 TA = +85°C -40 RF_ATTN = HIGH TA = +25°C TA = -40°C 5 MAX2371 toc13 TA = +25°C GAIN (dB) TA = -40°C 5 IIP3 (dBm) 0 10 GAIN (dB) 20 MAX2371 toc09 MAX2371 toc08 RF_ATTN = LOW 15 S12 -45 -25.0 0 1.7 2.2 2.7 -50 1.2 1.7 VAGC (V) 2.2 2.7 840 VAGC (V) 860 880 900 920 940 FREQUENCY (MHz) S11, S22, S12 vs. VAGC 0 -5 MAX2371 toc14 1.2 S11 -10 S11, S22, S12 (dB) P1dB (dBm) IIP3 vs. VAGC GAIN vs. VAGC 20 MAX2371 toc10 GAIN vs. FREQUENCY 20 -15 S22 -20 -25 S11 -30 RF_ATTN = LOW RF_ATTN = HIGH -35 -40 S12 -45 -50 1.2 1.7 2.2 2.7 VAGC (V) _______________________________________________________________________________________ 5 MAX2371/MAX2373 Typical Operating Characteristics (continued) (MAX2371/MAX2373 EV Kits, VCC = 2.775V, RX_EN = high, RSET = 1.1kΩ, LNA_I = high, TA = +25°C. For MAX2371, fRF = 150MHz; for MAX2373, fRF = 900MHz, unless otherwise noted.) MAX2371/MAX2373 LNAs with Step Attenuator and VGA Table 1. MAX2371 S-Parameters (VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25°C.) LNA (S11) FREQUENCY (MHz) MAGNITUDE PHASE 6 LNA (S21) LNA (S12) LNA (S22) MAGNITUDE PHASE MAGNITUDE PHASE MAGNITUDE PHASE 0.002136 -102.490 0.998803 -1.1632 -4.4481 10 0.943409 -4.8477 5.980672 171.1200 100 0.746965 -29.9420 2.959750 102.1900 0.002021 61.149 0.994752 150 0.728794 -35.6990 2.347308 89.6950 0.003089 138.790 0.985485 -6.0754 200 0.705066 -43.4190 1.769355 75.0130 0.003238 47.793 0.986870 -7.7399 300 0.704636 -55.1180 1.290313 58.1420 0.004439 83.493 0.979073 -11.1180 400 0.719615 -65.2420 1.060230 45.42700 0.003346 82.612 0.963130 -14.6680 500 0.731998 -73.5040 0.930754 36.0670 0.004395 68.614 0.947862 -18.0970 600 0.736258 -80.6450 0.849660 28.4990 0.006155 71.599 0.935998 -21.2670 700 0.738074 -85.6220 0.810047 22.7470 0.004143 56.224 0.930518 -23.5710 800 0.738465 -89.2240 0.796627 18.1080 0.005580 93.741 0.935158 -25.5640 900 0.736843 -91.6690 0.793643 14.3230 0.005309 89.871 0.933372 -27.8980 1000 0.720668 -94.0260 0.801946 9.9632 0.007592 99.418 0.941369 -30.2110 1100 0.712090 -96.1830 0.816554 5.9889 0.008451 122.090 0.940860 -32.2310 1200 0.690343 -98.0560 0.836893 1.1604 0.011955 129.220 0.936774 -34.6290 1300 0.657098 -100.3900 0.861113 -4.3698 0.014966 130.200 0.930219 -37.6190 1400 0.606583 -103.2500 0.891302 -10.2610 0.019602 131.440 0.925103 -40.1400 1500 0.545500 -106.6300 0.925092 -16.1910 0.023963 128.730 0.926670 -42.0800 1600 0.469143 -111.0400 0.966707 -23.1040 0.031521 121.710 0.939042 -43.7830 1700 0.372315 -116.0200 1.002767 -29.9130 0.039505 114.740 0.949456 -45.2980 1800 0.267147 -123.3900 1.021504 -37.6360 0.047321 109.530 0.966296 -46.5300 1900 0.150522 -137.6100 1.021081 -45.7240 0.056859 100.480 0.975001 -48.7600 2000 0.060478 160.4700 0.995004 -53.5490 0.063929 92.788 0.971740 -50.8360 _______________________________________________________________________________________ LNAs with Step Attenuator and VGA MAX2371/MAX2373 Table 2. MAX2373 S-Parameters (VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25°C.) LNA (S11) FREQUENCY (MHz) MAGNITUDE PHASE LNA (S21) LNA (S12) LNA (S22) MAGNITUDE PHASE MAGNITUDE PHASE MAGNITUDE PHASE 10 0.952248 -0.8171 7.273610 -178.830 0.002162 -89.276 1.000092 -0.8184 100 0.933405 -9.1461 7.077013 163.940 0.001346 78.684 0.993482 -2.3140 200 0.884179 -16.6570 6.529802 150.770 0.002137 32.634 0.991791 -3.8136 300 0.824784 -22.6500 5.929253 139.770 0.002217 72.860 0.983762 -5.6360 400 0.767609 -27.4800 5.400078 130.020 0.001332 86.532 0.971102 -7.2455 500 0.709643 -30.9910 4.904559 121.750 0.001641 86.431 0.958562 -8.9841 600 0.656682 -34.5840 4.431492 113.750 0.002297 70.617 0.955972 -10.7250 700 0.616673 -37.2530 4.016983 107.480 0.001701 105.050 0.946259 -12.1890 800 0.586388 -39.7830 3.644182 101.820 0.002688 73.619 0.941846 -13.4650 900 0.558837 -41.8580 3.313218 97.239 0.001077 143.410 0.933168 -15.1090 1000 0.536056 -42.9140 3.059039 92.435 0.001617 102.100 0.938912 -16.8900 1100 0.524439 -44.4030 2.805078 87.484 0.001442 151.320 0.932492 -18.5160 1200 0.516220 -45.9560 2.614027 82.687 0.002973 178.790 0.926200 -20.8080 1300 0.511487 -47.1900 2.417436 78.482 0.003764 -175.540 0.919094 -23.6930 1400 0.508259 -47.9420 2.253642 74.093 0.004195 -176.470 0.919952 -25.7200 1500 0.504028 -49.1020 2.090210 70.061 0.007366 -163.150 0.917498 -27.9410 1600 0.509736 -50.1550 1.975627 66.443 0.008200 -162.620 0.919486 -29.8050 1700 0.510000 -51.3530 1.841259 63.336 0.010929 -163.870 0.923092 -32.1340 1800 0.513009 -52.9500 1.719293 59.870 0.015327 -160.350 0.924634 -33.9510 1900 0.515994 -54.6510 1.597405 56.385 0.016692 -162.560 0.933781 -36.3470 2000 0.510141 -55.6650 1.467185 53.411 0.018843 -177.660 0.933039 -38.8240 Table 3. MAX2371 Typical Noise Parameters (VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25°C, data from design simulation.) FREQUENCY (MHz) NFMIN (dB) ΓOPT ∠ ΓOPT RN (Ω) 130 0.84 0.34 46.4 8.8 140 0.83 0.35 49.3 8.5 150 0.82 0.34 52.7 8.1 160 0.81 0.34 56.2 7.8 170 0.81 0.33 59.8 7.5 180 0.81 0.32 63.4 7.1 _______________________________________________________________________________________ 7 MAX2371/MAX2373 LNAs with Step Attenuator and VGA Table 4. MAX2373 Typical Noise Parameters (VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25°C, data from design simulation.) FREQUENCY (MHz) NFMIN (dB) ΓOPT ∠ ΓOPT RN (Ω) 850 870 890 910 930 950 1.06 1.08 1.10 1.11 1.13 1.15 0.35 0.35 0.34 0.34 0.33 0.33 60.5 61.8 63.3 64.7 66.2 67.7 10.02 9.98 9.94 9.90 9.86 9.82 Pin Description PIN NAME 1 LNA_IN RF Input. Requires DC-blocking capacitor and external matching network. 2 LNA_E LNA Emitter. Connect to GND with an inductor. See inductor value in Table 5. 3 RX_EN LNA Control. Set RX_EN high to enable LNA; set RX_EN low to disable LNA. 4 RF_ATTN 5 AGC AGC Input Voltage. Set AGC to VCC/2 for maximum gain. Set AGC to VCC - 200mV for minimum gain. If left unconnected, the LNA will operate at maximum gain and optimum noise figure. 6 LNA_I LNA Nominal Bias-Current Setting. Set LNA_I high for high-current mode. Set LNA_I low for low-current mode. If left unconnected, the default state of the LNA is high-current mode. 7 LNA_OUT RF Output Pin. Requires a pullup inductor to LNA_VCC and external matching network. 8 LNA_VCC Supply Voltage for the AGC Amplifier 9 AGC_BYP AGC Bypass. Connect a capacitor to ground. The value of the capacitor is a compromise of AGC response time and blocker frequency offset. 10 RSET External pin for precision resistor to ground to set reference bias current for IC; typical bias current is 50µA to 100µA. 11 RF_VCC Supply Voltage for the LNA. Bypass with a capacitor to GND as close to the pin as possible. Do NOT connect any tuned circuits to this supply pin. 12 GND Exposed Pad FUNCTION Attenuator Control. Set RF_ATTN high for low-gain mode; set RF_ATTN low for high-gain mode. Ground RF and DC Ground Table 5. Inductor Selection BAND 150MHz (VHF) L SERIES VALUE (nH) LNA TYPE 33 Low Band 450MHz (UHF) 10 Low Band 450MHz (UHF) 2.7 High Band 800MHz 2.5 High Band 1GHz 1.8 High Band Detailed Description The MAX2371/MAX2373 are single-channel, singleended, low-noise amplifiers with two gain modes and continuous automatic gain control (AGC) in both modes. The devices are intended as low-noise gain 8 stages for direct conversion receivers (DCR) or very low IF (VLIF) receivers. These devices provide high gain-control dynamic range (typ 60dB) at RF with excellent noise and reverse isolation characteristics. Vary the resistor at pin RSET and the inductor at LNA_E to meet a wide range of gain and linearity requirements. The ICs can be dynamically configured through pins LNA_I and RF_ATTN. When LNA_I is connected to VCC, the LNA is in high-current mode, nominally configured for maximum gain and low noise figure of the amplifier. If the LNA_I pin is grounded, the current of the LNA is reduced, and the associated gain, input IP3, and noise figure are degraded. The devices have two gain modes configured by the RF_ATTN pin. Set RF_ATTN high for low-gain mode; set RF_ATTN low for high-gain mode. The gain step between these two gain modes typically is 20dB. _______________________________________________________________________________________ LNAs with Step Attenuator and VGA Applications Information AGC The AGC of the MAX2371/MAX2373 is controlled by an external voltage at pin AGC. The amplifier is at full gain if the voltage at pin AGC is nominally VCC/2. It is at minimum gain if the voltage at pin AGC is VCC. The AGC attenuation range, which is continuously variable, is specified at 45dB. The IP3 will degrade slightly as AGC reduces the gain. The devices include two gain modes. Set RF_ATTN high to enable the low-gain mode, which reduces the gain by about 20dB. Low-gain mode will increase the system IP3 by approximately 18dB, which provides strong signal overload and IM protection. An external pin (RF_ATTN) controls switching between gain modes so this function can be combined with overall AGC control. AGC is independent of the choice of gain mode. The gain step between modes is in addition to the range of AGC, allowing a large overall gain-control range. AGC Response A linear transfer function between the AGC control signal and the AGC attenuation is realized in dB. The linear relationship in dB/V is maintained to ±10% over a specified attenuation range. Any compensation for gain-mode change must come from the AGC control. After reducing gain by switching the RF_ATTN pin, reduce the AGC voltage to achieve the desired overall gain. The LNA current also can be changed by toggling the LNA_I pin. This operation is independent of gain mode and AGC control. The low-current mode is intended as a second (reduced-current) quiescent point of operation for strong-signal operating environments. Matching Networks For best performance, match LNA_IN and LNA_OUT to 50Ω for the band of operation. Typical matching circuits for two bands (136MHz to 174MHz and 850MHz to 940MHz) are shown in the EV kit. The chip impedance changes minimally from low to high gain and with AGC. The input requires a DC-blocking capacitor. The size of this capacitor influences the startup time and IP3. There is a trade-off between these: A large DC-blocking capacitor means a good IP3 and slow startup. The maximum startup time is determined by the equation below: MAXTSTART = 40 ✕ CAC ✕ RSET, where CAC = AC-coupling cap in Farads, RSET = currentsetting resistor in Ω. IP3 will improve with the separation of the interfering tones, so a wider channel system can use a smaller DCblocking capacitor and achieve a better IP3. The customer also can change the emitter inductor at LNA_E to get the desired linearity and gain. Changing this inductor value requires a change to the input match. The output is an open collector and needs a pullup inductor. A load resistor also can be connected across it. The resistor determines the trade-off between the bandwidth of the match and the gain. A small load resistor means a wider match and lower gain. Layout Issues For best performance, pay attention to power-supply issues as well as to the layout of the RFOUT matching network. The EV kit can be used as a layout example. Ground connections followed by supply bypass are the most important. Power-Supply Bypassing The MAX2371/MAX2373 have two supply pins: LNA_VCC and RF_VCC. These must be bypassed separately. It is assumed that there is a large capacitor decoupling the power supply. LNA_VCC and RF_VCC are each decoupled with 1500pF (MAX2371) or 100pF (MAX2373) capacitor. Use separate paths to the ground plane for each of the bypass capacitors, and minimize trace length to reduce inductance. The exposed pad must be connected to system ground with very low impedance vias. Power-Supply Layout To minimize coupling between sections of the IC, the ideal power-supply layout is a star configuration with a large decoupling capacitor at a central VCC node. The VCC traces branch from this central node, each to a separate VCC node in the PC board. At the end of each trace is a bypass capacitor that has low ESR at the RF of operation. This arrangement provides local decoupling at each VCC pin. At high frequencies, any signal leaking out of one supply pin sees a relatively high impedance (formed by the VCC trace inductance) to the central VCC node and an even higher impedance to any other supply pin, as well as a low impedance to ground through the bypass capacitor. _______________________________________________________________________________________ 9 MAX2371/MAX2373 The MAX2371/MAX2373 can be turned off in transmit or battery-save standby mode. The receive-enable pin (RX_EN) also can turn off the devices even if VCC is not removed, because multiple LNAs can be connected to the same VCC for multiband applications. The devices allow external matching networks to configure operation in a wide frequency range. Refer to the EV kit schematic for a guide to designing the matching network. MAX2371/MAX2373 LNAs with Step Attenuator and VGA Typical Operating Circuits 1.1kΩ PRECISION 2.775 VDC GND RF_VCC RSET AGC_BYP RF INPUT MATCH MAX2371 MAX2373 LNA_IN LNA_E RF ATTENUATOR LNA_VCC AGC AMP LNA LNA_OUT RX_EN EXPONENTIAL CONVERTER RF_ATTN AGC LNA_I Chip Information Impedance-Matching Network Layout The input- and output-matching networks are sensitive to layout-related parasitic inductions. To minimize parasitic inductance, keep traces short and place components as close as possible to the chip. To minimize parasitic capacitance, minimize the area of the plane. TRANSISTOR COUNT: 360 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit 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 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.