MAXIM MAX2371, MAX2373 Technical data

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.

Applications

Direct Conversion Receiver (DCR)

Very Low IF Receiver

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

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

19-2301; Rev 1; 10/06

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.

EVALUATION KIT

AVAILABLE

PART

TEMP RANGE

PIN­PACKAGE

PKG

CODE

MAX2371EGC

12 QFN-EP*

G1233-1

MAX2371ETC

T1233-3

MAX2371ETC+

T1233+3

MAX2373EGC

12 QFN-EP*

G1233-1

MAX2373ETC

T1233-3

MAX2373ETC+

T1233+3

TOP VIEW

12

GND11RF_V

CC

10

RSET

45

AGC6LNA_I

1

2LNA_E

3

9

8

7RX_EN

AGC_BYP

LNA_V

CC

LNA_OUT

MAX2371
MAX2373

LNA_IN

RF_ATTN

QFN/TQFN

Pin Configuration

AGC

RF_V

CC

GND

LNA_OUT

LNA_IN

AGC_BYP

EXPONENTIAL

CONVERTER

AGC
AMP

LNA

RF_ATTN

RF

ATTENUATOR

LNA_V

CC

LNA_I

RX_EN

LNA_E

RSET

MAX2371
MAX2373

Functional Diagram

*EP = Exposed pad.
+Denotes lead-free package.

-40°C to +85°C

-40°C to +85°C 12 TQFN-EP*

-40°C to +85°C 12 TQFN-EP*

-40°C to +85°C

-40°C to +85°C 12 TQFN-EP*

-40°C to +85°C 12 TQFN-EP*

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(VCC= 2.775V, RX_EN = high, R

SET

= 1.1kΩ, V

AGC

= VCC/2, TA= -40°C to +85°C. Typical values are at TA= +25°C, unless other-

wise noted.)

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.

VCCto GND...........................................................-0.3V to +3.6V

All Pins Excluding Grounds to Pin GND.....-0.3V to (V

CC

+ 0.3V)

LNA Input Power (RX_EN = low) ........................................5dBm

Continuous Power Dissipation (T

A

= +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

PARAMETER

CONDITIONS

UNITS

Supply Voltage V

CC

V

RX_EN = low, VCC = 3.3V 0.5 20 µA

LNA_I = high, RF_ATTN = low 3.5 5.5 mASupply Current I

CC

LNA_I = low 2.5 3.5 mA

Digital Input Logic High V

IH

Pins LNA_I, RF_ATTN, RX_EN 0.7 ✕ V

CC

V

Digital Input Logic Low V

IL

Pins LNA_I, RF_ATTN, RX_EN 0

V

Logic Pin Impedance Logic pins RX_EN, RF_ATTN, LNA_I 50 kΩ

AGC Pin Impedance Pins AGC

kΩ

AC ELECTRICAL CHARACTERISTICS

(MAX2371/MAX2373 EV Kits, VCC= 2.65V to 3.3V, RX_EN = high, R

SET

= 1.1kΩ, TA= -40°C to +85°C. Typical values are at VCC=

2.775V; for MAX2371 f

RF

= 150MHz, for MAX2373 fRF= 850MHz to 940MHz; TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER CONDITIONS

UNITS

LNA AND AGC AMP CHARACTERISTICS

Low band (MAX2371)

Radio Frequency Range (Note 2)

High band (MAX2373)

MHz

MAX2371 -12

LNA_I = high;
RF_ATTN = low

MAX2373 -15

MAX2371 -14 -10

Input Return Loss (S11)
(Note 3)

LNA_I = high;
RF_ATTN = high

MAX2373 -10

dB

MAX2371 -40 -35

Reverse Isolation (S12) Over AGC range

MAX2373 -42 -35

dB

MAX2371 13

16

LNA_I = high, TA =
+25°C, V

CC

= 2.775V

MAX2373 14

17

MAX2371

12

Max Power Gain (Note 3)

LNA_I = low, T

A

=

+25°C, V

CC

= 2.775V

MAX2373

13

dB

Gain Variation Over Temperature TA = -40°C to +85°C, V

AGC

< 1.8V

2.0 dB

SYMBOL

MIN TYP MAX

2.65 2.775 3.30

0.3 ✕ V

100

MIN TYP MAX

136 150 174

850 900 940

14.5

15.5

10.5

10.5

-2.0

V

CC

CC

-9.5

-9.5

-6.5

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

_______________________________________________________________________________________ 3

AC ELECTRICAL CHARACTERISTICS (continued)

(MAX2371/MAX2373 EV Kits, VCC= 2.65V to 3.3V, RX_EN = high, R

SET

= 1.1kΩ, TA= -40°C to +85°C. Typical values are at VCC=

2.775V; for MAX2371 f

RF

= 150MHz, for MAX2373 fRF= 850MHz to 940MHz; TA= +25°C, unless otherwise noted.) (Note 1)

PARAMETER CONDITIONS

UNITS

V

AGC

= 1.275V 1.8 2.2

V

AGC

= 1.575V 5.0 7.7

V

AGC

= 1.875V 11

LNA_I = high, TA =
+25°C, V

CC

= 2.775V,

RF_ATTN = low

V

AGC

= 2.175V 20

SSB Noise Figure vs. AGC

LNA_I = low, T

A

=

+25°C, V

CC

= 2.775V,

RF_ATTN = low

V

AGC

= 1.275V 2.1 2.6

dB

LNA_I = high

RF_ATTN = low,
V

AGC

< 1.8V

LNA_I = low -24 -22

LNA_I = high -3 0

Input 1dB Compression Point

RF_ATTN = high,
V

AGC

< 1.8V

LNA_I = low -9

dBm

LNA_I = high -5 -1

-7 -4

RF_ATTN = low,
V

AGC

= VCC/2

-12 -9

dBm

Input IP3 (Notes 4, 5)

RF_ATTN = high,

LNA_I = high 9 13

dBm

MAX2371

-8

Input IP3 Over AGC Range

RF_ATTN = low, LNA_I = high,
V

AGC

= V

CC

/2 to 1.80V

MAX2373

dBm

AGC RESPONSE

AGC Attenuation Range (Note 6)

V

CC

= 2.775V, RF_ATTN = low, V

AGC

= 1.3375V

to 2.575V, T

A

= +25°C

35 45 dB

RF_ATTN = low, V

AGC

= 1.625V 32 40 47

AGC Slope Over Control Range

RF_ATTN = high, V

AGC

= 1.625V 24 33 41

dB/V

RF STEP ATTENUATOR

MAX2371

Gain Step

RF_ATTN = high to low,
LNA_I = high

MAX2373

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

IN1

= 150MHz, f

IN2

= 150.1MHz, PIN= -30dBm for both tones (MAX2371).

Note 5: f

IN1

= 900MHz, f

IN2

= 900.1MHz, PIN= -30dBm for both tones (MAX2373).

Note 6: Parameters are guaranteed by production test.

V

AGC

= V

/2 to 2.575V

CC

LNA_I = low

MIN TYP MAX

14.5

-21.5 19.5

-6.5

MAX2371

MAX2373

-10.5

-12.5 -10.5

16.0 17.5 19.0

18.0 19.5 21.0

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

4 _______________________________________________________________________________________

Typical Operating Characteristics

(MAX2371/MAX2373 EV Kits, VCC= 2.775V, RX_EN = high, R

SET

= 1.1kΩ, LNA_I = high, TA= +25°C. For MAX2371, fRF= 150MHz;

for MAX2373, fRF= 900MHz, unless otherwise noted.)

GAIN vs. FREQUENCY

MAX2371 toc01

FREQUENCY (MHz)

GAIN (dB)

170160150140

-5

0

5

10

15

20

-10
130 180

TA = +85°C

TA = -40°C

TA = +25°C

RF_ATTN = LOW

RF_ATTN = HIGH

GAIN vs. V

AGC

MAX2371 toc02

V

AGC

(V)

GAIN (dB)

2.42.01.6

-50

-40

-30

-20

-10

0

10

20

-60

1.2 2.8

RF_ATTN = LOW

RF_ATTN = HIGH

TA = +85°C

TA = +25°C

TA = -40°C

IIP3 vs. V

AGC

MAX2371 toc03

V

AGC

(V)

IIP3 (dBm)

1.71.61.4 1.5

-10

-5

0

5

10

15

20

25

-15

1.3 1.8

RF_ATTN = LOW

RF_ATTN = HIGH

TA = +85°C

TA = +25°C

TA = -40°C

P

1dB

vs. V

AGC

MAX2371 toc04

V

AGC

(V)

P

1dB

(dBm)

2.72.21.7

-20.0

-15.0

-10.0

-5.0

0

5.0

10.0

-25.0

1.2

TA = +25°C

RF_ATTN = LOW

RF_ATTN = HIGH

TA = +85°C

TA = -40°C

NOISE FIGURE vs. V

AGC

MAX2371 toc05

V

AGC

(V)

NOSIE FIGURE (dB)

2.72.21.7

5

10

15

20

25

30

0

1.2

RF_ATTN = LOW

RF_ATTN = HIGH

S11, S22, S12 vs. FREQUENCY

MAX2371 toc06

FREQUENCY (MHz)

S11, S22, S12 (dB)

170160150140

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-50
130 180

S22

S11

S12

RF_ATTN = LOW RF_ATTN = HIGH

S11, S22, S12 vs. V

AGC

MAX2371 toc07

V

AGC

(V)

S11, S22, S12 (dB)

2.72.21.7

-50

-40

-30

-20

-10

0

-60

1.2

S22

S11

S11

S12

RF_ATTN = HIGH

RF_ATTN = LOW

MAX2371

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

_______________________________________________________________________________________ 5

IIP3 vs. V

AGC

MAX2371 toc10

V

AGC

(V)

IIP3 (dBm)

1.71.61.51.4

-10

-5

0

5

10

15

20

-15

1.3 1.8

RF_ATTN = LOW

RF_ATTN = HIGH

TA = -40°C

TA = +25°C

TA = +85°C

P

1dB

vs. V

AGC

MAX2371 toc11

V

AGC

(V)

P

1dB

(dBm)

2.72.21.7

-20.0

-15.0

-10.0

-5.0

0

5.0

10.0

-25.0

1.2

TA = -40°C

TA = 85°C

TA = +25°C

RF_ATTN = LOW

RF_ATTN = HIGH

NOISE FIGURE vs. V

AGC

MAX2371 toc12

V

AGC

(V)

NOSIE FIGURE (dB)

2.72.21.7

5

10

15

20

25

30

0

1.2

RF_ATTN = LOW

RF_ATTN = HIGH

Typical Operating Characteristics (continued)

(MAX2371/MAX2373 EV Kits, VCC= 2.775V, RX_EN = high, R

SET

= 1.1kΩ, LNA_I = high, TA= +25°C. For MAX2371, fRF= 150MHz;

for MAX2373, fRF= 900MHz, unless otherwise noted.)

S11, S22, S12 vs. FREQUENCY

MAX2371 toc13

FREQUENCY (MHz)

S11, S22, S12 (dB)

920900880860

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-50
840 940

S22

S11

S12

S11

RF_ATTN = LOW RF_ATTN = HIGH

S11, S22, S12 vs. V

AGC

MAX2371 toc14

V

AGC

(V)

S11, S22, S12 (dB)

2.72.21.7

-35

-40

-30

-25

-20

-15

-10

-5

0

-50

-45

1.2

S22

S11

S11

S12

RF_ATTN = HIGH

RF_ATTN = LOW

GAIN vs. FREQUENCY

MAX2371 toc08

FREQUENCY (MHz)

GAIN (dB)

920900880860

-5

0

5

10

15

20

-10
840 940

TA = +85°C

TA = -40°C

TA = +25°C

RF_ATTN = LOW

RF_ATTN = HIGH

GAIN vs. V

AGC

MAX2371 toc09

V

AGC

(V)

GAIN (dB)

2.42.01.6

-40

-30

-20

-10

0

10

20

-50

1.2 2.8

RF_ATTN = LOW

RF_ATTN = HIGH

TA = -40°C

TA = +25°C

TA = +85°C

MAX2373

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

6 _______________________________________________________________________________________

Table 1. MAX2371 S-Parameters

(VCC= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN= -30dBm, TA= +25°C.)

LNA (S11) LNA (S21) LNA (S12) LNA (S22)

FREQUENCY

(MHz)

PHASE

PHASE

PHASE

PHASE

10

-4.8477

0.002136 -102.490

-1.1632

100

-29.9420

0.002021 61.149

-4.4481

150

-35.6990

89.6950 0.003089 138.790

-6.0754

200

-43.4190

75.0130 0.003238 47.793

-7.7399

300

-55.1180

58.1420 0.004439 83.493

-11.1180

400

-65.2420

0.003346 82.612

-14.6680

500

-73.5040

36.0670 0.004395 68.614

-18.0970

600

-80.6450

28.4990 0.006155 71.599

-21.2670

700

-85.6220

22.7470 0.004143 56.224

-23.5710

800

-89.2240

18.1080 0.005580 93.741

-25.5640

900

-91.6690

14.3230 0.005309 89.871

-27.8980

1000

-94.0260

9.9632 0.007592 99.418

-30.2110

1100

-96.1830

5.9889 0.008451 122.090

-32.2310

1200

-98.0560

1.1604 0.011955 129.220

-34.6290

1300

-4.3698 0.014966 130.200

-37.6190

1400

-10.2610 0.019602 131.440

-40.1400

1500

-16.1910 0.023963 128.730

-42.0800

1600

-23.1040 0.031521 121.710

-43.7830

1700

-29.9130 0.039505 114.740

-45.2980

1800

-37.6360 0.047321 109.530

-46.5300

1900

-45.7240 0.056859 100.480

-48.7600

2000

-53.5490 0.063929 92.788

-50.8360

MAGNITUDE

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 -100.3900 0.861113

0.606583 -103.2500 0.891302

0.545500 -106.6300 0.925092

0.469143 -111.0400 0.966707

0.372315 -116.0200 1.002767

0.267147 -123.3900 1.021504

0.150522 -137.6100 1.021081

0.060478 160.4700 0.995004

MAGNITUDE

5.980672 171.1200

2.959750 102.1900

2.347308

1.769355

1.290313

1.060230 45.42700

0.930754

0.849660

0.810047

0.796627

0.793643

0.801946

0.816554

0.836893

MAGNITUDE

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

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

_______________________________________________________________________________________ 7

Table 2. MAX2373 S-Parameters

(VCC= 2.775V, RX_EN = high, LNA_I = high, RF_ATTN = low, PIN= -30dBm, TA= +25°C.)

LNA (S11) LNA (S21) LNA (S12) LNA (S22)

FREQUENCY

(MHz)

PHASE

PHASE

PHASE

PHASE

10

-0.8171

-178.830 0.002162 -89.276

-0.8184

100

-9.1461

163.940 0.001346 78.684

-2.3140

200

-16.6570

150.770 0.002137 32.634

-3.8136

300

-22.6500

139.770 0.002217 72.860

-5.6360

400

-27.4800

130.020 0.001332 86.532

-7.2455

500

-30.9910

121.750 0.001641 86.431

-8.9841

600

-34.5840

113.750 0.002297 70.617

-10.7250

700

-37.2530

107.480 0.001701 105.050

-12.1890

800

-39.7830

101.820 0.002688 73.619

-13.4650

900

-41.8580

97.239 0.001077 143.410

-15.1090

1000

-42.9140

92.435 0.001617 102.100

-16.8900

1100

-44.4030

87.484 0.001442 151.320

-18.5160

1200

-45.9560

82.687 0.002973 178.790

-20.8080

1300

-47.1900

78.482 0.003764 -175.540

-23.6930

1400

-47.9420

74.093 0.004195 -176.470

-25.7200

1500

-49.1020

70.061 0.007366 -163.150

-27.9410

1600

-50.1550

66.443 0.008200 -162.620

-29.8050

1700

-51.3530

63.336 0.010929 -163.870

-32.1340

1800

-52.9500

59.870 0.015327 -160.350

-33.9510

1900

-54.6510

56.385 0.016692 -162.560

-36.3470

2000

-55.6650

53.411 0.018843 -177.660

-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) NF

MIN

(dB) ⎜Γ

OPT

⎟∠ Γ

OPT

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

MAGNITUDE

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

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

MAGNITUDE

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

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

8 _______________________________________________________________________________________

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

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.

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) NF

MIN

(dB) ⎜Γ

OPT

⎟∠ Γ

OPT

RN (Ω)

850 1.06 0.35 60.5 10.02
870 1.08 0.35 61.8 9.98
890 1.10 0.34 63.3 9.94
910 1.11 0.34 64.7 9.90
930 1.13 0.33 66.2 9.86
950 1.15 0.33 67.7 9.82

Pin Description

PIN NAME FUNCTION

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

Attenuator Control. Set RF_ATTN high for low-gain mode; set RF_ATTN low for high-gain mode.

5 AGC

AGC Input Voltage. Set AGC to V

CC

/2 for maximum gain. Set AGC to V

CC

- 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

RF Output Pin. Requires a pullup inductor to LNA_VCC and external matching network.

8

Supply Voltage for the AGC Amplifier

9

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_V

CC

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 Ground

EP

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.

Table 5. Inductor Selection

RF_ATTN

LNA_OUT

LNA_V

CC

AGC_BYP

BAND

150MHz (VHF) 33 Low Band

450MHz (UHF) 10 Low Band

450MHz (UHF) 2.7 High Band

800MHz 2.5 High Band

1GHz 1.8 High Band

L SERIES VALUE

(nH)

LNA TYPE

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

_______________________________________________________________________________________ 9

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 VCCis not
removed, because multiple LNAs can be connected to
the same VCCfor 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.

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:

MAXT

START

= 40 ✕ C

AC

✕ R

SET

,

where CAC= AC-coupling cap in Farads, R

SET

= current-

setting 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_VCCand RF_VCC. These must be bypassed sepa­rately. It is assumed that there is a large capacitor
decoupling the power supply. LNA_VCCand RF_V

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.

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 VCCnode. The
VCCtraces branch from this central node, each to a sep­arate VCCnode 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 VCCpin. At high frequencies, any signal leaking
out of one supply pin sees a relatively high impedance
(formed by the VCCtrace inductance) to the central V

CC

node and an even higher impedance to any other supply
pin, as well as a low impedance to ground through the
bypass capacitor.

MAX2371/MAX2373

LNAs with Step Attenuator and VGA

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.

_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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

AGC

RF_V

CCGND

LNA_OUT

LNA_IN

2.775 V

DC

AGC_BYP

EXPONENTIAL

CONVERTER

AGC

AMP

LNA

RF_ATTN

RF

ATTENUATOR

RF

INPUT MATCH

LNA_V

CC

LNA_I

RSET

1.1kΩ

PRECISION

RX_EN

LNA_E

MAX2371
MAX2373

Typical Operating Circuits

Revision History

Pages changed at Rev 1: 1, 8, 10