19-2301; Rev 1; 10/06
KIT
ATION
EVALU
E
L
B
AVAILA
LNAs with Step Attenuator and VGA
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.
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
Ordering Information
TEMP RANGE
PINPACKAGE
PKG
CODE
MAX2371EGC
-40°C to +85°C
12 QFN-EP*
G1233-1
Direct Conversion Receiver (DCR)
MAX2371ETC
-40°C to +85°C
12 TQFN-EP*
T1233-3
Very Low IF Receiver
MAX2371ETC+ -40°C to +85°C
12 TQFN-EP*
T1233+3
G1233-1
PART
Applications
MAX2373EGC
-40°C to +85°C
12 QFN-EP*
MAX2373ETC
-40°C to +85°C
12 TQFN-EP*
T1233-3
MAX2373ETC+ -40°C to +85°C
12 TQFN-EP*
T1233+3
*EP = Exposed pad.
+Denotes lead-free package.
Pin Configuration
Functional Diagram
TOP VIEW
GND
GND
12
11
10
AGC_BYP
MAX2371
MAX2373
LNA_IN
LNA_IN
1
9
AGC_BYP
LNA_E
2
8
LNA_VCC
RX_EN
3
7
LNA_OUT
MAX2371
MAX2373
4
RSET
RF_VCC
RF_VCC RSET
5
RF_ATTN AGC
LNA_E
RF
ATTENUATOR
RX_EN
LNA
LNA_VCC
AGC
AMP
LNA_OUT
EXPONENTIAL
CONVERTER
6
LNA_I
RF_ATTN
AGC
LNA_I
QFN/TQFN
________________________________________________________________ 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
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
Low band (MAX2371)
136
150
174
High band (MAX2373)
850
900
940
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)
LNA_I = high;
RF_ATTN = low
MAX2371
-12
-9.5
MAX2373
-15
-9.5
LNA_I = high;
RF_ATTN = high
MAX2371
-14
-10
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
MAX2373
-10
-6.5
MAX2371
-40
-35
MAX2373
-42
-35
MAX2371
13
14.5
16
MAX2373
14
15.5
17
MAX2371
10.5
12
MAX2373
10.5
13
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
TYP
MAX
VAGC = 1.275V
MIN
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
MAX2371
-7
-4
MAX2373
-12
-9
9
13
LNA_I = low
LNA_I = high
RF_ATTN = low, LNA_I = high,
VAGC = VCC/2 to 1.80V
MAX2371
-10.5
-8
MAX2373
-12.5
-10.5
35
45
UNITS
dB
2.6
dBm
dBm
dBm
dBm
AGC RESPONSE
AGC Attenuation Range (Note 6)
AGC Slope Over Control Range
VCC = 2.775V, RF_ATTN = low, VAGC = 1.3375V
to 2.575V, TA = +25°C
dB
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
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
0
15
-10
10
-20
TA = +85°C
-30
0
RF_ATTN = HIGH
-5
TA = -40°C
-50
-10
RF_ATTN = HIGH
RF_ATTN = LOW
-60
-10
140
150
160
170
-15
1.2
180
1.6
2.0
P1dB vs. VAGC
TA = +85°C
-10.0
25
-15.0
20
15
10
5
-25.0
0
1.7
2.2
2.7
S22
-5
-10
-20
S11
-25
RF_ATTN = LOW
-30
1.2
-40
1.7
2.2
2.7
S12
130
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
S12
-60
1.2
1.7
2.2
2.7
VAGC (V)
4
160
FREQUENCY (MHz)
0
-50
RF_ATTN = HIGH
-50
VAGC (V)
-20
1.8
-15
-45
1.2
1.7
-35
RF_ATTN = LOW
RF_ATTN = LOW
-20.0
1.6
0
S11, S22, S12 (dB)
TA = +25°C
1.5
S11, S22, S12 vs. FREQUENCY
RF_ATTN = HIGH
NOSIE FIGURE (dB)
0
TA = -40°C
1.4
VAGC (V)
30
MAX2371 toc04
RF_ATTN = HIGH
-5.0
1.3
NOISE FIGURE vs. VAGC
10.0
5.0
2.8
2.4
VAGC (V)
FREQUENCY (MHz)
MAX2371 toc05
130
TA = -40°C
0
TA = +25°C
-40
-5
TA = +25°C
TA = +85°C
5
MAX2371 toc06
TA = +85°C TA = +25°C
5
GAIN (dB)
GAIN (dB)
10
RF_ATTN = HIGH
20
IIP3 (dBm)
15
25
MAX2371 toc02
MAX2371 toc01
RF_ATTN = LOW
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
10
0.943409
-4.8477
5.980672
171.1200
0.002136
-102.490
0.998803
-1.1632
100
0.746965
-29.9420
2.959750
102.1900
0.002021
61.149
0.994752
-4.4481
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
-0.8171
7.273610
-178.830
0.002162
-89.276
1.000092
-0.8184
10
0.952248
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
2
3
LNA_IN
LNA_E
RX_EN
FUNCTION
4
RF_ATTN
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.
5
AGC
6
LNA_I
7
8
LNA_OUT
LNA_VCC
9
AGC_BYP
10
RSET
11
RF_VCC
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
50µA to 100µA.
12
GND
EP
Exposed
Pad
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
Internally connected to GND. Connect to a large ground plane to maximize thermal performance.
Do not use as the sole ground connection point.
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
capacitor means a good IP3 and slow startup. The maximum startup time is determined by the equation below:
Applications Information
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.
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
MAXTSTART = 40 ✕ CAC ✕ RSET,
where CAC = AC-coupling cap in Farads, RSET = currentsetting resistor in Ω.
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
Revision History
Pages changed at Rev 1: 1, 8, 10
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.
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