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19-2301; Rev 0A; 6/02
KIT ATION EVALU ILABLE AVA
LNAs with Step Attenuator and VGA
Features
o Low Noise Figure (1.8dB typical) o High Small-Signal Gain (15dB Nominal) o Wide Frequency Range of Operation (100MHz to 1GHz) o 20dB Step Attenuator o 45dB AGC Range Excluding Step Attenuator o 2.65V to 3.3V Single-Supply Operation o Shutdown Mode o 3.5mA Supply Current, Adjustable Down to 2.5mA o 40dB Reverse Isolation
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. 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.
MAX2371/MAX2373
Applications
Direct Conversion Receiver (DCR) Very Low IF Receiver
PART MAX2371EGC MAX2373EGC
Ordering Information
TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 12 QFN 12 QFN
Pin Configuration
GND RSET TOP VIEW RF_VCC
GND
Functional Diagram
RF_VCC RSET
12 LNA_IN LNA_E RX_EN 1 2 3
11
10 9 AGC_BYP LNA_VCC LNA_OUT
AGC_BYP LNA_IN MAX2371 MAX2373 LNA_VCC
MAX2371 MAX2373
8 7
LNA_E
RF ATTENUATOR
LNA
AGC AMP
LNA_OUT
RX_EN
EXPONENTIAL CONVERTER
4 RF_ATTN
5 AGC
6 LNA_I
RF_ATTN AGC LNA_I
________________________________________________________________ Maxim Integrated Products
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LNAs with Step Attenuator and VGA MAX2371/MAX2373
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 = +70C) 12-Pin QFN (derate 11.9mW/C above +70C) ...........952mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Soldering Temperature (10s) ...........................................+300C
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 = 1.1k, VAGC = VCC/2, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.)
PARAMETER Supply Voltage Supply Current Digital Input Logic High Digital Input Logic Low Logic Pin Impedance AGC Pin Impedance SYMBOL VCC RX_EN = low, VCC = 3.3V ICC VIH VIL LNA_I = high, RF_ATTN = low LNA_I = low Pins LNA_I, RF_ATTN, RX_EN Pins LNA_I, RF_ATTN, RX_EN Logic pins RX_EN, RF_ATTN, LNA_I Pins AGC 0.7 VCC 0 50 100 CONDITIONS MIN 2.65 TYP 2.775 0.5 3.5 2.5 MAX 3.30 20 5.5 3.5 VCC 0.3 VCC UNITS V A mA mA V V k k
AC ELECTRICAL CHARACTERISTICS
(MAX2371/MAX2373 EV Kits, VCC = 2.65V to 3.3V, RX_EN = high, RSET = 1.1k, TA = -40C to +85C. Typical values are at VCC = 2.775V; for MAX2371 fRF = 150MHz, for MAX2373 fRF = 850MHz to 940MHz; TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER LNA AND AGC AMP CHARACTERISTICS Radio Frequency Range (Note 2) Low band (MAX2371) High band (MAX2373) LNA_I = high; RF_ATTN = low LNA_I = high; RF_ATTN = high Over AGC range LNA_I = high, TA = +25C, VCC = 2.775V LNA_I = low, TA = +25C, VCC = 2.775V Gain Variation Over Temperature MAX2371 MAX2373 MAX2371 MAX2373 MAX2371 MAX2373 MAX2371 MAX2373 MAX2371 MAX2373 13 14 10.5 10.5 -2.0 136 850 150 900 -12 -15 -14 -10 -40 -42 14.5 15.5 12 13 2.0 dB 174 940 -9.5 -9.5 -10 -6.5 -35 -35 16 17 dB dB dB MHz CONDITIONS MIN TYP MAX UNITS
Input Return Loss (S11) (Note 3)
Reverse Isolation (S12)
Max Power Gain (Note 3)
TA = -40C to +85C, VAGC < 1.8V
2
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LNAs with Step Attenuator and VGA
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2371/MAX2373 EV Kits, VCC = 2.65V to 3.3V, RX_EN = high, RSET = 1.1k, TA = -40C to +85C. Typical values are at VCC = 2.775V; for MAX2371 fRF = 150MHz, for MAX2373 fRF = 850MHz to 940MHz; TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER CONDITIONS VAGC = 1.275V LNA_I = high, TA = +25C, VCC = 2.775V, RF_ATTN = low SSB Noise Figure vs. AGC LNA_I = low, TA = +25C, VCC = 2.775V, RF_ATTN = low 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 AGC RESPONSE AGC Attenuation Range (Note 6) AGC Slope Over Control Range RF STEP ATTENUATOR Gain Step RF_ATTN = high to low, LNA_I = high MAX2371 MAX2373 16.0 18.0 17.5 19.5 19.0 21.0 dB VCC = 2.775V, RF_ATTN = low, VAGC = 1.3375V to 2.575V, TA = +25C RF_ATTN = low, VAGC = 1.625V RF_ATTN = high, VAGC = 1.625V 35 32 24 45 40 33 47 41 dB dB/V VAGC = 1.575V VAGC = 1.875V VAGC = 2.175V VAGC = 1.275V LNA_I = high LNA_I = low LNA_I = high LNA_I = low LNA_I = high LNA_I = low LNA_I = high MAX2371 MAX2373 MAX2371 MAX2373 -21.5 -24 -3 -9 -5 -7 -12 9 -10.5 -12.5 MIN TYP 1.8 5.0 11 20 2.1 19.5 -22 0 -6.5 -1 -4 -9 13 -8 -10.5 dBm dBm dBm dBm 2.6 MAX 2.2 7.7 14.5 dB UNITS
MAX2371/MAX2373
Input 1dB Compression Point
RF_ATTN = low, LNA_I = high, VAGC = VCC/2 to 1.80V
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6:
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.
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LNAs with Step Attenuator and VGA MAX2371/MAX2373
Typical Operating Characteristics
(MAX2371/MAX2373 EV Kits, VCC = 2.775V, RX_EN = high, RSET = 1.1k, LNA_I = high, TA = +25C. For MAX2371, fRF = 150MHz; for MAX2373, fRF = 900MHz, unless otherwise noted.)
MAX2371
GAIN vs. FREQUENCY
MAX2371 toc01
GAIN vs. VAGC
MAX2371 toc02
IIP3 vs. VAGC
RF_ATTN = HIGH 20 15 IIP3 (dBm) 10 5 0 TA = +85C TA = +25C TA = -40C
MAX2371 toc03
20 RF_ATTN = LOW 15 10 GAIN (dB) 5 0 -5 -10 130 140 150 160 170 RF_ATTN = HIGH TA = +85C TA = +25C TA = -40C
20 RF_ATTN = LOW 10 0 GAIN (dB) -10 -20 -30 -40 -50 -60 TA = +85C TA = +25C TA = -40C RF_ATTN = HIGH
25
-5 -10 RF_ATTN = LOW -15 2.8 1.3 1.4 1.5 1.6 1.7 1.8
180
1.2
1.6
2.0 VAGC (V)
2.4
FREQUENCY (MHz)
VAGC (V)
P1dB vs. VAGC
MAX2371 toc04
NOISE FIGURE vs. VAGC
MAX2371 toc05
S11, S22, S12 vs. FREQUENCY
-5 -10 S11, S22, S12 (dB) -15 -20 -25 -30 -35 RF_ATTN = LOW RF_ATTN = HIGH S11 S22
MAX2371 toc06
10.0 5.0 0 P1dB (dBm) -5.0 -10.0 -15.0 RF_ATTN = LOW -20.0 -25.0 1.2 1.7 VAGC (V) 2.2 2.7 TA = -40C TA = +25C TA = +85C RF_ATTN = HIGH
30 RF_ATTN = HIGH 25 NOSIE FIGURE (dB) 20 15 10 RF_ATTN = LOW 5 0 1.2 1.7 VAGC (V) 2.2 2.7
0
-40 -45 -50 130 140 150 160 170 180 FREQUENCY (MHz) S12
S11, S22, S12 vs. VAGC
S11 -10 S11, S22, S12 (dB) -20 -30 -40 -50 -60 1.2 1.7 VAGC (V) 2.2 2.7 S12 S22 S11 RF_ATTN = LOW RF_ATTN = HIGH
MAX2371 toc07
0
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LNAs with Step Attenuator and VGA
Typical Operating Characteristics (continued)
(MAX2371/MAX2373 EV Kits, VCC = 2.775V, RX_EN = high, RSET = 1.1k, LNA_I = high, TA = +25C. For MAX2371, fRF = 150MHz; for MAX2373, fRF = 900MHz, unless otherwise noted.)
MAX2371/MAX2373
MAX2373
GAIN vs. FREQUENCY
MAX2371 toc08
GAIN vs. VAGC
MAX2371 toc09
IIP3 vs. VAGC
RF_ATTN = HIGH 15 10 IIP3 (dBm) 5 0 -5 -10 TA = -40C TA = +25C TA = +85C
MAX2371 toc10
20 RF_ATTN = LOW 15 10 GAIN (dB)
20 RF_ATTN = LOW 10 0 GAIN (dB) -10 -20 -30 TA = -40C TA = +25C TA = +85C RF_ATTN = HIGH -50
20
5 0 -5
TA = -40C
TA = +25C
TA = +85C
RF_ATTN = HIGH -10 840 860 880 900 920 940 FREQUENCY (MHz)
-40
RF_ATTN = LOW -15 2.8 1.3 1.4 1.5 1.6 1.7 1.8
1.2
1.6
2.0 VAGC (V)
2.4
VAGC (V)
P1dB vs. VAGC
MAX2371 toc11
NOISE FIGURE vs. VAGC
MAX2371 toc12
S11, S22, S12 vs. FREQUENCY
-5 -10 S11, S22, S12 (dB) -15 -20 -25 -30 -35 -40 -45 S12 S11 RF_ATTN = LOW RF_ATTN = HIGH S22 S11
MAX2371 toc13
10.0 5.0 0 P1dB (dBm) -5.0 -10.0 -15.0 RF_ATTN = LOW -20.0 -25.0 1.2 1.7 VAGC (V) 2.2 2.7 TA = -40C TA = +25C TA = 85C RF_ATTN = HIGH
30 25 NOSIE FIGURE (dB) 20 15 RF_ATTN = LOW 10 5 0 1.2 1.7 VAGC (V) 2.2 2.7 RF_ATTN = HIGH
0
-50 840 860 880 900 920 940 FREQUENCY (MHz)
S11, S22, S12 vs. VAGC
-5 -10 S11, S22, S12 (dB) -15 -20 -25 -30 -35 -40 -45 -50 1.2 1.7 VAGC (V) 2.2 2.7 S12 S22 S11 RF_ATTN = LOW RF_ATTN = HIGH S11
MAX2371 toc14
0
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LNAs with Step Attenuator and VGA MAX2371/MAX2373
Table 1. MAX2371 S-Parameters
(VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25C.)
LNA (S11) FREQUENCY (MHz) MAGNITUDE PHASE 10 100 150 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 0.943409 0.746965 0.728794 0.705066 0.704636 0.719615 0.731998 0.736258 0.738074 0.738465 0.736843 0.720668 0.712090 0.690343 0.657098 0.606583 0.545500 0.469143 0.372315 0.267147 0.150522 0.060478 -4.8477 -29.9420 -35.6990 -43.4190 -55.1180 -65.2420 -73.5040 -80.6450 -85.6220 -89.2240 -91.6690 -94.0260 -96.1830 -98.0560 -100.3900 -103.2500 -106.6300 -111.0400 -116.0200 -123.3900 -137.6100 160.4700 LNA (S21) MAGNITUDE 5.980672 2.959750 2.347308 1.769355 1.290313 1.060230 0.930754 0.849660 0.810047 0.796627 0.793643 0.801946 0.816554 0.836893 0.861113 0.891302 0.925092 0.966707 1.002767 1.021504 1.021081 0.995004 PHASE 171.1200 102.1900 89.6950 75.0130 58.1420 45.42700 36.0670 28.4990 22.7470 18.1080 14.3230 9.9632 5.9889 1.1604 -4.3698 -10.2610 -16.1910 -23.1040 -29.9130 -37.6360 -45.7240 -53.5490 LNA (S12) MAGNITUDE 0.002136 0.002021 0.003089 0.003238 0.004439 0.003346 0.004395 0.006155 0.004143 0.005580 0.005309 0.007592 0.008451 0.011955 0.014966 0.019602 0.023963 0.031521 0.039505 0.047321 0.056859 0.063929 PHASE -102.490 61.149 138.790 47.793 83.493 82.612 68.614 71.599 56.224 93.741 89.871 99.418 122.090 129.220 130.200 131.440 128.730 121.710 114.740 109.530 100.480 92.788 LNA (S22) MAGNITUDE 0.998803 0.994752 0.985485 0.986870 0.979073 0.963130 0.947862 0.935998 0.930518 0.935158 0.933372 0.941369 0.940860 0.936774 0.930219 0.925103 0.926670 0.939042 0.949456 0.966296 0.975001 0.971740 PHASE -1.1632 -4.4481 -6.0754 -7.7399 -11.1180 -14.6680 -18.0970 -21.2670 -23.5710 -25.5640 -27.8980 -30.2110 -32.2310 -34.6290 -37.6190 -40.1400 -42.0800 -43.7830 -45.2980 -46.5300 -48.7600 -50.8360
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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 = +25C.)
LNA (S11) FREQUENCY (MHz) MAGNITUDE PHASE 10 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 0.952248 0.933405 0.884179 0.824784 0.767609 0.709643 0.656682 0.616673 0.586388 0.558837 0.536056 0.524439 0.516220 0.511487 0.508259 0.504028 0.509736 0.510000 0.513009 0.515994 0.510141 -0.8171 -9.1461 -16.6570 -22.6500 -27.4800 -30.9910 -34.5840 -37.2530 -39.7830 -41.8580 -42.9140 -44.4030 -45.9560 -47.1900 -47.9420 -49.1020 -50.1550 -51.3530 -52.9500 -54.6510 -55.6650 LNA (S21) MAGNITUDE 7.273610 7.077013 6.529802 5.929253 5.400078 4.904559 4.431492 4.016983 3.644182 3.313218 3.059039 2.805078 2.614027 2.417436 2.253642 2.090210 1.975627 1.841259 1.719293 1.597405 1.467185 PHASE -178.830 163.940 150.770 139.770 130.020 121.750 113.750 107.480 101.820 97.239 92.435 87.484 82.687 78.482 74.093 70.061 66.443 63.336 59.870 56.385 53.411 LNA (S12) MAGNITUDE 0.002162 0.001346 0.002137 0.002217 0.001332 0.001641 0.002297 0.001701 0.002688 0.001077 0.001617 0.001442 0.002973 0.003764 0.004195 0.007366 0.008200 0.010929 0.015327 0.016692 0.018843 PHASE -89.276 78.684 32.634 72.860 86.532 86.431 70.617 105.050 73.619 143.410 102.100 151.320 178.790 -175.540 -176.470 -163.150 -162.620 -163.870 -160.350 -162.560 -177.660 LNA (S22) MAGNITUDE 1.000092 0.993482 0.991791 0.983762 0.971102 0.958562 0.955972 0.946259 0.941846 0.933168 0.938912 0.932492 0.926200 0.919094 0.919952 0.917498 0.919486 0.923092 0.924634 0.933781 0.933039 PHASE -0.8184 -2.3140 -3.8136 -5.6360 -7.2455 -8.9841 -10.7250 -12.1890 -13.4650 -15.1090 -16.8900 -18.5160 -20.8080 -23.6930 -25.7200 -27.9410 -29.8050 -32.1340 -33.9510 -36.3470 -38.8240
Table 3. MAX2371 Typical Noise Parameters
(VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25C, data from design simulation.)
FREQUENCY (MHz) 130 140 150 160 170 180 NFMIN (dB) 0.84 0.83 0.82 0.81 0.81 0.81 OPT 0.34 0.35 0.34 0.34 0.33 0.32 OPT 46.4 49.3 52.7 56.2 59.8 63.4 RN () 8.8 8.5 8.1 7.8 7.5 7.1
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LNAs with Step Attenuator and VGA MAX2371/MAX2373
Table 4. MAX2373 Typical Noise Parameters
(VCC = 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN = -30dBm, TA = +25C, data from design simulation.)
FREQUENCY (MHz) 850 870 890 910 930 950 NFMIN (dB) 1.06 1.08 1.10 1.11 1.13 1.15 OPT 0.35 0.35 0.34 0.34 0.33 0.33 OPT 60.5 61.8 63.3 64.7 66.2 67.7 RN () 10.02 9.98 9.94 9.90 9.86 9.82
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11 12 NAME LNA_IN LNA_E RX_EN RF_ATTN AGC LNA_I LNA_OUT LNA_VCC AGC_BYP RSET RF_VCC GND FUNCTION RF Input. Requires DC-blocking capacitor and external matching network. LNA Emitter. Connect to GND with an inductor. See inductor value in Table 5. LNA Control. Set RX_EN high to enable LNA; set RX_EN low to disable LNA. Attenuator Control. Set RF_ATTN high for low-gain mode; set RF_ATTN low for high-gain mode. 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. 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. RF Output Pin. Requires a pullup inductor to LNA_VCC and external matching network. Supply Voltage for the AGC Amplifier AGC Bypass. Connect a capacitor to ground. The value of the capacitor is a compromise of AGC response time and blocker frequency offset. External pin for precision resistor to ground to set reference bias current for IC; typical bias current is 50A to 100A. 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. Ground RF and DC Ground
Exposed Pad
Table 5. Inductor Selection
BAND 150MHz (VHF) 450MHz (UHF) 450MHz (UHF) 800MHz 1GHz L SERIES VALUE (nH) 33 10 2.7 2.5 1.8 LNA TYPE Low Band Low Band High Band High Band High Band
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.
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
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LNAs with Step Attenuator and VGA
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. 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 . 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.
MAX2371/MAX2373
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.
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.
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.
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
Matching Networks
For best performance, match LNA_IN and LNA_OUT to 50 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
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LNAs with Step Attenuator and VGA MAX2371/MAX2373
Typical Operating Circuits
2.775 VDC GND RF_VCC
1.1k PRECISION RSET
AGC_BYP RF INPUT MATCH LNA_IN
MAX2371 MAX2373
LNA_VCC
LNA_E
RF ATTENUATOR
LNA
AGC AMP
LNA_OUT
RX_EN EXPONENTIAL CONVERTER
RF_ATTN
AGC
LNA_I
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
Chip Information
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