Analog-Devices-Inc–Maxim-Integrated-MAX2371ETC-
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19-2301; Rev 1; 10/06
LNAs with Step Attenuator and VGA
General Description
Features
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 con-
trol (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.
♦
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
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 con-
figured 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, lin-
early controlled gain states, and shutdown mode.
♦
3.5mA Supply Current, Adjustable Down to 2.5mA
♦
40dB Reverse Isolation
Ordering Information
PIN-
PACKAGE
PKG
CODE
PART
TEMP RANGE
Applications
Direct Conversion Receiver (DCR)
MAX2371
EGC -40°C
to +85°C
12 QFN-EP*
MAX2371ETC -40°C
to +85°C
12 TQFN-EP*
G1233-1
T1233-3
T1233+3
G1233-1
T1233-3
T1233+3
MAX2371ETC+ -40°C
to +85°C
12 TQFN-EP*
Very Low IF Receiver
MAX2373
EGC -40°C
to +85°C
12 QFN-EP*
MAX2373ETC
-40°C to +85°C
12 TQFN-EP*
MAX2373ETC+ -40°C
to +85°C
12 TQFN-EP*
*
EP = Exposed pad.
+
Denotes lead-free package.
Pin Configuration
Functional Diagram
TOP VIEW
RSET
GND
RF_V
CC
GND RF_V
RSET
10
CC
12
11
AGC_BYP
LNA_V
LNA_IN
MAX2371
MAX2373
CC
LNA_IN
LNA_E
RX_EN
1
2
3
9
8
7
AGC_BYP
RF
AGC
AMP
LNA
LNA_OUT
ATTENUATOR
LNA_E
RX_EN
LNA_V
CC
MAX2371
MAX2373
LNA_OUT
EXPONENTIAL
CONVERTER
4
5
6
RF_ATTN
AGC
LNA_I
RF_ATTN AGC
LNA_I
QFN/TQFN
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
LNAs with Step Attenuator and VGA
ABSOLUTE MAXIMUM RATINGS
CC
All Pins Excluding Grounds to Pin GND…..-0.3V to (V
LNA Input Power (RX_EN = low) ………………………………….5dBm
V
to GN
D
.
………………………………………………….-0.3V to +3.6V
Operating Temperature Range ………………………-40°C to +85°C
Junction Temperatur
e
.
……………………………………………..+150°C
Storage Temperature Rang
e
.
……………………….-65°C to +160°C
Soldering Temperature (10s
)
.
……………………………………+300°C
+ 0.3V)
CC
Continuous Power Dissipation (T
= +70°C)
A
12-Pin QFN (derate 11.9mW/°C above +70°C) ………..952mW
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
(V
= 2.775V, RX_EN = high, R
= 1.1k
Ω
, V
= V
/2, T
= -40°C to +85°C. Typical values are at T
= +25°C, unless other-
CC
SET
AGC
CC
A
A
wise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
2.775
0.5
MAX
3.30
20
UNITS
V
Supply Voltage
Supply Current
V
2.65
CC
RX_EN = low, V
= 3.3V
µA
mA
mA
V
CC
I
LNA_I = high, RF_ATTN = low
LNA_I = low
3.5
5.5
CC
2.5
3.5
✕
Digital Input Logic High
Digital Input Logic Low
Logic Pin Impedance
AGC Pin Impedance
V
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
V
V
CC
IH
CC
✕
V
0
0.3
V
V
IL
CC
50
k
Ω
k
Ω
100
AC ELECTRICAL CHARACTERISTICS
(MAX2371/MAX2373 EV Kits, V
= 2.65V to 3.3V, RX_EN = high, R
= 1.1k
Ω
, T
= -40°C to +85°C. Typical values are at V
=
CC
SET
A
CC
2.775V; for MAX2371 f
= 150MHz, for MAX2373 f
= 850MHz to 940MHz; T
= +25°C, unless otherwise noted.) (Note 1)
RF
RF
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LNA AND AGC AMP CHARACTERISTICS
Low band (MAX2371)
High band (MAX2373)
136
850
150
900
-12
-15
-14
-10
-40
-42
14.5
15.5
12
174
940
-9.5
-9.5
-10
-6.5
-35
-35
16
Radio Frequency Range (Note 2)
MHz
dB
MAX2371
MAX2373
MAX2371
MAX2373
MAX2371
MAX2373
MAX2371
MAX2373
MAX2371
MAX2373
< 1.8V
LNA_I = high;
RF_ATTN = low
Input Return Loss (S11)
(Note 3)
LNA_I = high;
RF_ATTN = high
Reverse Isolation (S12)
Over AGC range
dB
13
14
LNA_I = high, T
=
A
+25°C, V
= 2.775V
CC
17
Max Power Gain (Note 3)
dB
dB
10.5
10.5
-2.0
LNA_I = low, T
=
A
+25°C, V
= 2.775V
CC
13
Gain Variation Over Temperature
T
= -40°C to +85°C, V
2.0
A
AGC
2
_______________________________________________________________________________________
LNAs with Step Attenuator and VGA
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2371/MAX2373 EV Kits, V
= 2.65V to 3.3V, RX_EN = high, R
= 1.1k
Ω
, T
= -40°C to +85°C. Typical values are at V
=
CC
CC
SET
A
2.775V; for MAX2371 f
= 150MHz, for MAX2373 f
= 850MHz to 940MHz; T
= +25°C, unless otherwise noted.) (Note 1)
RF
RF
A
PARAMETER
CONDITIONS
MIN
TYP
1.8
5.0
11
MAX
2.2
UNITS
V
V
V
V
= 1.275V
= 1.575V
= 1.875V
= 2.175V
AGC
AGC
AGC
AGC
LNA_I = high, T
=
A
7.7
+25°C, V
= 2.775V,
CC
14.5
RF_ATTN = low
SSB Noise Figure vs. AGC
dB
20
LNA_I = low, T
=
A
+25°C, V
= 2.775V,
V
= 1.275V
2.1
2.6
CC
AGC
RF_ATTN = low
LNA_I = high
LNA_I = low
LNA_I = high
LNA_I = low
LNA_I = high
-21.5
-24
-3
19.5
-22
0
RF_ATTN = low,
V
< 1.8V
AGC
Input 1dB Compression Point
Input IP3 (Notes 4, 5)
dBm
dBm
RF_ATTN = high,
< 1.8V
V
AGC
-9
-6.5
-1
-5
RF_ATTN = low,
= V
/2
MAX2371
MAX2373
-7
-4
V
AGC
CC
LNA_I = low
LNA_I = high
-12
-9
RF_ATTN = high,
= V
/2 to 2.575V
9
13
dBm
dBm
V
AGC
CC
MAX2371
MAX2373
-10.5
-12.5
-8
RF_ATTN = low, LNA_I = high,
Input IP3 Over AGC Range
AGC RESPONSE
V
= V
/2 to 1.80V
CC
AGC
-10.5
V
= 2.775V, RF_ATTN = low, V
= 1.3375V
CC
AGC
AGC Attenuation Range (Note 6)
35
45
dB
to 2.575V, T
= +25°C
A
RF_ATTN = low, V
= 1.625V
32
24
40
33
47
41
AGC
AGC Slope Over Control Range
RF STEP ATTENUATOR
Gain Step
dB/V
RF_ATTN = high, V
= 1.625V
AGC
MAX2371
MAX2373
16.0
18.0
17.5
19.5
19.0
21.0
RF_ATTN = high to low,
LNA_I = high
dB
Note 1:
Parameters over temperature and supply voltage range are guaranteed by design and characterization, unless otherwise noted.
Note 2:
Operation outside these frequency bands is possible but has not been characterized. See
Typical Operating Characteristics
.
Note 3:
Measured with external matching network.
Note 4:
f
Note 5:
f
= 150MHz, f
= 900MHz, f
= 150.1MHz, P
= -30dBm for both tones (MAX2371).
IN1
IN1
IN2
IN2
IN
= 900.1MHz, P
= -30dBm for both tones (MAX2373).
IN
Note 6:
Parameters are guaranteed by production test.
_______________________________________________________________________________________
3
LNAs with Step Attenuator and VGA
T
y
pical Operating Characteristics
(MAX2371/MAX2373 EV Kits, V
CC
= 2.775V, RX_EN = high, R
= 1.1k
Ω
, LNA_I = high, T
= +25°C. For MAX2371, f
= 150MHz;
A RF
SET
for MAX2373, f
= 900MHz, unless otherwise noted.)
RF
MAX2371
GAIN vs. FREQUENCY
GAIN vs. V
IIP3 vs. V
AGC
AGC
20
15
10
5
20
10
25
20
15
10
5
RF_ATTN = HIGH
RF_ATTN = LOW
RF_ATTN = LOW
0
-10
-20
-30
-40
-50
-60
T
= -40
°
C
T
= +25
°
C
T
= +85
°
C
A
A
A
T
= +85
°
C
T
= +25
°
C
T =
-40
°
C
A
A
A
T
= +85
°
C
A
0
0
T
= +25
°
C
A
-5
T
= -40
°
C
-5
-10
A
RF_ATTN = HIGH
-10
-15
RF_ATTN = HIGH
2.4 2.8
RF_ATTN = LOW
1.4
130
140
150
160
170
180
1.2
1.6
2.0
1.3
1.5
1.6
(V)
1.7
1.8
FREQUENCY (MHz)
V
(V)
V
AGC
AGC
P
1dB
vs. V
NOISE FIGURE vs. V
AGC
S11, S22, S12 vs. FREQUENCY
AGC
10.0
5.0
30
25
20
15
10
5
0
-5
S22
RF_ATTN = HIGH
RF_ATTN = HIGH
-10
-15
-20
-25
-30
-35
-40
-45
-50
0
S11
-5.0
-10.0
-15.0
-20.0
-25.0
T
= +85
°
C
T
= -40
°
C
T
= +25
°
C
A
A
A
RF_ATTN = LOW
RF_ATTN = HIGH
RF_ATTN = LOW
RF_ATTN = LOW
2.2
S12
130
0
1.2
1.7
2.7
1.2
1.7
2.2
2.7
140
150
160
170
180
V
(V)
V
(V)
AGC
FREQUENCY (MHz)
AGC
S11, S22, S12 vs. V
AGC
0
-10
-20
-30
-40
-50
-60
S11
S22
S11
RF_ATTN = HIGH
RF_ATTN = LOW
S12
1.2
1.7
2.2
2.7
V
(V)
AGC
4
_______________________________________________________________________________________
LNAs with Step Attenuator and VGA
T
y
pical Operating Characteristics (continued)
(MAX2371/MAX2373 EV Kits, V
CC
= 2.775V, RX_EN = high, R
= 1.1k
Ω
, LNA_I = high, T
= +25°C. For MAX2371, f
= 150MHz;
A RF
SET
for MAX2373, f
= 900MHz, unless otherwise noted.)
RF
MAX2373
GAIN vs. V
IIP3 vs. V
GAIN vs. FREQUENCY
AGC
AGC
20
15
10
5
20
15
10
5
20
10
RF_ATTN = HIGH
RF_ATTN = LOW
RF_ATTN = LOW
0
T
= +85
°
C
T
= +25
°
C
T
= -40
°
C
A
A
A
-10
-20
-30
-40
-50
T
= -40
°
C
T
= +25
°
C
T =
+85
°
C
A
A
A
0
T
= -40
°
C
A
0
T
= +25
°
C
-5
A
-5
-10
T
= +85
°
C
A
-10
-15
RF_ATTN = HIGH
RF_ATTN = HIGH
2.4 2.8
RF_ATTN = LOW
1.4
1.3
1.5
1.6
(V)
1.7
1.8
840
860
880
900
920
940
1.2
1.6
2.0
V
FREQUENCY (MHz)
V
(V)
AGC
AGC
P
1dB
vs. V
AGC
NOISE FIGURE vs. V
S11, S22, S12 vs. FREQUENCY
AGC
10.0
5.0
30
25
20
15
10
5
0
-5
S11
RF_ATTN = HIGH
-10
-15
-20
-25
-30
-35
-40
-45
-50
S22
0
RF_ATTN = HIGH
-5.0
-10.0
-15.0
-20.0
-25.0
T
= -40
°
C
T
= +25
°
C
T
= 85
°
C
A
A
A
S11
RF_ATTN = LOW
RF_ATTN = HIGH
RF_ATTN = LOW
RF_ATTN = LOW
2.2
S12
0
1.2
1.7
2.7
1.2
1.7
2.2
(V)
2.7
840
860
880
900
920
940
V
(V)
V
AGC
FREQUENCY (MHz)
AGC
S11, S22, S12 vs. V
AGC
0
-5
S11
-10
-15
-20
S22
S11
-25
-30
-35
RF_ATTN = HIGH
RF_ATTN = LOW
-40
-45
-50
S12
1.2
1.7
2.2
2.7
V
(V)
AGC
_______________________________________________________________________________________
5
LNAs with Step Attenuator and VGA
Table 1. MAX2371 S-Parameters
(V
= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, P
= -30dBm, T
= +25°C.)
IN A
CC
LNA (S11)
LNA (S21)
LNA (S12)
LNA (S22)
FREQUENCY
(MHz)
MAGNITUDE
PHASE
-4.8477
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
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
MAGNITUDE
PHASE
-1.1632
10
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
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
100
-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
-4.4481
150
138.790
47.793
-6.0754
200
-7.7399
300
83.493
-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
400
82.612
500
68.614
600
71.599
700
56.224
800
93.741
900
89.871
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
99.418
5.9889
122.090
129.220
130.200
131.440
128.730
121.710
114.740
109.530
100.480
92.788
1.1604
-4.3698
-10.2610
-16.1910
-23.1040
-29.9130
-37.6360
-45.7240
-53.5490
6
_______________________________________________________________________________________
LNAs with Step Attenuator and VGA
Table 2. MAX2373 S-Parameters
(V
= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, P
= -30dBm, T
= +25°C.)
IN A
CC
LNA (S11)
LNA (S21)
LNA (S12)
LNA (S22)
FREQUENCY
(MHz)
MAGNITUDE
PHASE
-0.8171
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
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
MAGNITUDE
PHASE
-0.8184
10
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
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
100
-9.1461
-2.3140
200
-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
32.634
-3.8136
300
72.860
-5.6360
400
86.532
-7.2455
500
86.431
-8.9841
600
70.617
-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
700
105.050
73.619
800
900
143.410
102.100
151.320
178.790
-175.540
-176.470
-163.150
-162.620
-163.870
-160.350
-162.560
-177.660
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
Table 3. MAX2371 Typical Noise Parameters
(V
= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, P
= -30dBm, T
= +25°C, data from design simulation.)
CC
IN
A
FREQUENCY (MHz)
NF
(dB)
⎜Γ
⎟
∠ Γ
R (
Ω
)
N
MIN
OPT
OPT
130
140
150
160
170
180
0.84
0.83
0.82
0.81
0.81
0.81
0.34
0.35
0.34
0.34
0.33
0.32
46.4
8.8
8.5
8.1
7.8
7.5
7.1
49.3
52.7
56.2
59.8
63.4
_______________________________________________________________________________________
7
LNAs with Step Attenuator and VGA
Table 4. MAX2373 Typical Noise Parameters
(V
= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, P
= -30dBm, T
= +25°C, data from design simulation.)
CC
IN
A
FREQUENCY (MHz)
NF
(dB)
⎜Γ
⎟
∠ Γ
R (
Ω
)
N
MIN
OPT
OPT
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
10.02
9.98
9.94
9.90
9.86
9.82
61.8
63.3
64.7
66.2
67.7
Pin Description
PIN
1
NAME
LNA_IN
LNA_E
RX_EN
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.
2
3
4
RF_ATTN
Attenuator Control. Set RF_ATTN high for low-gain mode; set RF_ATTN low for high-gain mode.
AGC Input Voltage. Set AGC to V
/2 for maximum gain. Set AGC to V
– 200mV for minimum gain.
If
left unconnected, the LNA will operate at maximum gain and optimum noise figure.
CC
CC
5
6
AGC
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.
LNA_I
7
8
LNA_OUT
RF Output Pin. Requires a pullup inductor to LNA_V
Supply Voltage for the AGC Amplifier
and external matching network.
CC
LNA_V
CC
AGC Bypass. Connect a capacitor to ground. The value of the capacitor is a compromise of AGC
response time and blocker frequency offset.
9
AGC_BYP
RSET
External pin for precision resistor to ground to set reference bias current for IC; typical bias current is
50µA to 100µA.
10
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.
11
12
EP
RF_V
CC
GND
Ground
Exposed
Pad
Internally connected to GND. Connect to a large ground plane to maximize thermal performance.
Do not use as the sole ground connection point.
stages for direct conversion receivers (DCR) or very
Table 5. Inductor Selection
low IF (VLIF) receivers. These devices provide high
gain-control dynamic range (typ 60dB) at RF with
excellent noise and reverse isolation characteristics.
L SERIES VALUE
BAND
(nH)
LNA TYPE
Vary the resistor at pin RSET and the inductor at LNA_E
to meet a wide range of gain and linearity require-
ments. The ICs can be dynamically configured through
pins LNA_I and RF_ATTN. When LNA_I is connected to
150MHz (VHF)
450MHz (UHF)
450MHz (UHF)
800MHz
33
10
Low Band
Low Band
High Band
High Band
High Band
2.7
2.5
1.8
V
, the LNA is in high-current mode, nominally config-
CC
ured 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.
1GHz
Detailed Description
The MAX2371/MAX2373 are single-channel, single-
ended, 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
_______________________________________________________________________________________
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 V
is not
capacitor means a good IP3 and slow startup. The maxi-
mum startup time is determined by the equation below:
CC
removed, because multiple LNAs can be connected to
the same V
for multiband applications.
MAXT
= 40
✕
C
✕
R
AC SET
,
START
CC
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.
where C
= AC-coupling cap in Farads, R
AC
= current-
SET
setting resistor in
Ω
.
IP3 will improve with the separation of the interfering
tones, so a wider channel system can use a smaller DC-
blocking capacitor and achieve a better IP3. The cus-
tomer also can change the emitter inductor at LNA_E to
get the desired linearity and gain. Changing this induc-
tor value requires a change to the input match. The out-
put is an open collector and needs a pullup inductor. A
load resistor also can be connected across it. The resis-
tor determines the trade-off between the bandwidth of
the match and the gain. A small load resistor means a
wider match and lower gain.
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 V
/2. It is at min-
CC
imum gain if the voltage at pin AGC is V
. The AGC
CC
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 inde-
pendent of the choice of gain mode. The gain step
between modes is in addition to the range of AGC, allow-
ing 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_V
and RF_V
. These must be bypassed sepa-
CC
CC
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
10ꢀ over a speci-
fied 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.
rately. It is assumed that there is a large capacitor
decoupling the power supply. LNA_V
and RF_V
CC
CC
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.
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 V
node. The
CC
V
traces branch from this central node, each to a sep-
CC
Matching Networks
For best performance, match LNA_IN and LNA_OUT to
50
Ω
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
arate V
node in the PC board. At the end of each
CC
trace is a bypass capacitor that has low ESR at the RF of
operation. This arrangement provides local decoupling
at each V
pin. At high frequencies, any signal leaking
CC
out of one supply pin sees a relatively high impedance
(formed by the V
trace inductance) to the central V
CC
CC
node and an even higher impedance to any other supply
pin, as well as a low impedance to ground through the
bypass capacitor.
_______________________________________________________________________________________
9
LNAs with Step Attenuator and VGA
T
y
pical Operating Circuits
1.1k
Ω
PRECISION
2.775 V
DC
RF_V
GND
CC
RSET
AGC_BYP
MAX2371
MAX2373
LNA_IN
RF
LNA_V
CC
INPUT MATCH
RF
LNA_E
RX_EN
AGC
AMP
LNA
ATTENUATOR
LNA_OUT
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.
Chip Information
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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