Maxim MAX2440EAI, MAX2442EAI, MAX2441EAI Datasheet

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General Description

The MAX2440/MAX2441/MAX2442 highly integrated
front-end receiver ICs provide the lowest cost solution for
cordless phones and ISM-band radios operating in the
900MHz band. All devices incorporate receive image­reject mixers to reduce filter cost. They operate with a
+2.7V to +4.8V power supply, allowing direct connection
to a 3-cell battery stack.

The signal path incorporates an adjustable-gain LNA
and an image-reject downconverter with 35dB image
suppression. These features yield excellent combined
downconverter noise figure (4dB) and high linearity with
an input third-order intercept point (IP3) of up to +2dBm.

All devices include an on-chip local oscillator (LO),
requiring only an external varactor-tuned LC tank for
operation. The integrated divide-by-64/65 dual-modulus
prescaler can also be set to a direct mode, in which it
acts as an LO buffer amplifier. Three separate power­down inputs can be used for system power manage­ment, including a 0.5µA shutdown mode. These parts
are compatible with commonly used modulation
schemes such as FSK, BPSK, and QPSK, as well as fre­quency hopping and direct sequence spread-spectrum
systems. All devices come in a 28-pin SSOP package.

Evaluation kits are available for the MAX2420/
MAX2421/MAX2422. The MAX2420/MAX2421/MAX2422
are transceivers whose receive sections and pinout are
identical to the MAX2440/MAX2441/MAX2442.

For complete transceiver devices, refer to the MAX2420/
MAX2421/MAX2422/MAX2460/MAX2463 and MAX2424/
MAX2426 data sheets.

________________________Applications

Cordless Phones Spread-Spectrum Communications
Wireless Telemetry Two-Way Paging
Wireless Networks

Features

♦ Receive Mixer with 35dB Image Rejection
♦ Adjustable-Gain LNA
♦ Up to +2dBm Combined Receiver Input IP3
♦ 4dB Combined Receiver Noise Figure
♦ Low Current Consumption: 23mA Receive

9.5mA Oscillator

♦ 0.5µA Shutdown Mode
♦ Operates from Single +2.7V to +4.8V Supply

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

________________________________________________________________

Maxim Integrated Products

1

28
27
26
25
24
23
22
21
20
19
18
17
16
15

1
2
3
4
5
6
7
8

9
10
11
12
13
14

GND
GND
GND

TANK

GND

PREOUT
PREGND

MOD
DIV1
VCOON
RXON

GND

GND

GND

LNAGAIN

GND

GND

GND

RXIN

GND

RXOUT

CAP1

SSOP

TOP VIEW

MAX2440
MAX2441
MAX2442

TANK

V

CC

V

CC

V

CC

V

CC

V

CC

___________________Pin Configuration

19-1352; Rev 0; 4/98

PART

MAX2440EAI
MAX2441EAI
MAX2442EAI

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

28 SSOP
28 SSOP
28 SSOP

_______________Ordering Information

Functional Diagram appears at end of data sheet.

High side

INJECTION

TYPE

fRF+ 10.7

LO FREQ

(MHz)

High side

High side

fRF+ 70

fRF+ 46

MAX2442

MAX2441

70

46

MAX2440

PART

10.7

IF FREQ

(MHz)

______________________Selector Guide

EVALUATION KIT

AVAILABLE

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(VCC= +2.7V to +4.8V, no RF signals applied, LNAGAIN = unconnected, V

VCOON

= 2.4V, V

RXON

= V

MOD

= V

DIV1

= 0.45V, PREGND

= GND, T

A

= T

MIN

to T

MAX

. Typical values are at TA= +25°C, VCC= +3.3V, unless otherwise 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.

Note 1: Calculated by measuring the combined oscillator and prescaler supply current and subtracting the oscillator supply current.
Note 2: Calculated by measuring the combined oscillator and LO buffer supply current and subtracting the oscillator supply current.
Note 3: Calculated by measuring the combined receive and oscillator supply current and subtracting the oscillator supply current.

With LNAGAIN = GND, the supply current drops by 4.5mA.

V

CC

to GND...........................................................-0.3V to +5.5V

Voltage on LNAGAIN, RXON, VCOON,

DIV1, MOD ...............................................-0.3V to (V

CC

+ 0.3V)

RXIN Input Power..............................................................10dBm

TANK,

TANK Input Power...................................................2dBm

Continuous Power Dissipation (T

A

= +70°C)

SSOP (derate 9.50mW/°C above +70°C) ......................762mW

Operating Temperature Range

MAX244_EAI.....................................................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +165°C

Lead Temperature (soldering, 10sec).............................+300°C

PARAMETER

MIN TYP MAX UNITS

Receive Supply Current 23 36 mA

Prescaler Supply Current
(buffer mode)

5.4 8.5 mA

Oscillator Supply Current

Supply-Voltage Range 2.7 4.8 V

9.5 14 mA

Prescaler Supply Current
(divide-by-64/65 mode)

4.2 6 mA

CONDITIONS

V

RXON

= 2.4V, PREGND = unconnected (Note 3)

V

DIV1

= 2.4V (Note 2)

PREGND = unconnected

(Note 1)

Digital Input Voltage Low 0.45 V

0.5

RXON, DIV1, VCOON, MOD

VCOON = RXON = MOD =
DIV1 = GND

Digital Input Current ±1 ±10 µAVoltage on any one digital input = VCCor GND

Digital Input Voltage High V2.4RXON, DIV1, VCOON, MOD

Shutdown Supply Current

10

µA

TA= +25°C
TA= T

MIN

to T

MAX

MAX2442

AC ELECTRICAL CHARACTERISTICS

(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f

RXIN

= 915MHz; P

RXIN

= -35dBm; V

LNAGAIN

= 2V; V

VCOON

= V

RXON

= 2.4V; RXON = MOD = DIV1 = PREGND = GND; TA= +25°C;

unless otherwise noted.)

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

_______________________________________________________________________________________ 3

CONDITIONS UNITSMIN TYP MAXPARAMETER

MHz800 1000

36 46 55

8.5 10.7 12.5
MHz

20 22 24.5

dB

26 35Image Frequency Rejection

55 70 85

19.5 25

12

19 21 23.5

(Note 6)

-16

(Notes 4, 7) dBm

-8

Input Third-Order Intercept

-19 -17

(Note 8) ns500Receiver Turn-On Time

Receiver on or off dBm-60LO to RXIN Leakage

V

LNAGAIN

= 1V

dBm

-18

Input 1dB Compression

LNAGAIN = V

CC

-26

18 24

LNAGAIN = VCC,
TA= T

MIN

to T

MAX

(Note 4)

4 5

dB

12

Noise Figure

RECEIVER

dB

IF Frequency Range

(Notes 4, 5)

(Notes 4, 5)

Input Frequency Range

Conversion Power Gain

DIV1 = V

CC

(Notes 4, 6)

MAX2441
MAX2442

LNAGAIN = V

CC

V

LNAGAIN

= 1V

V

LNAGAIN

= 1V

LNAGAIN = V

CC

MAX2442

V

LNAGAIN

= 1V

LNAGAIN = GND

MAX2440

LNAGAIN = VCC,
TA= +25°C

MAX2440/MAX2441

MAX2440/MAX2441
MAX2442

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

4 _______________________________________________________________________________________

AC ELECTRICAL CHARACTERISTICS (continued)

(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f

RXIN

= 915MHz; P

RXIN

= -35dBm; V

LNAGAIN

= 2V; V

VCOON

= V

RXON

= 2.4V; RXON = MOD = DIV1 = PREGND = GND; TA= +25°C;

unless otherwise noted.)

Oscillator Phase Noise

Oscillator Frequency Range 690 1100 MHz

82 dBc/Hz

8

(Notes 4, 9)

10kHz offset (Note 10)
Standby to RX

Note 4: Guaranteed by design and characterization.
Note 5: Image rejection typically falls to 30dBc at the frequency extremes.
Note 6: Refer to the

Typical Operating Characteristics

for plots showing receiver gain versus LNAGAIN voltage, input IP3 versus

LNAGAIN voltage, and noise figure versus LNAGAIN voltage.

Note 7: Two tones at P

RXIN

= -45dBm each, f1 = 915.0MHz and f2 = 915.2MHz.

Note 8: Time delay from RXON = 0.45V to RXON = 2.4V transition to the time the output envelope reaches 90% of its final value.
Note 9: Refers to useable operating range. Tuning range of any given tank circuit design is typically much narrower (refer to Figure 1).
Note 10: Using tank components shown in Figure 1.
Note 11: This approximates a typical application in which a transmitter is followed by an external PA and a T/R switch with finite

isolation.

Note 12: Relative to the rising edge of PREOUT.

Prescaler Output Level

500 mVp-p

-11 -8

Required Modulus Setup Time 10 ns

ZL= 100kΩ

| |

10pF

Divide-by-64/65 mode (Notes 4, 12)

Required Modulus Hold Time 0 ns

Divide-by-64/65 mode (Notes 4, 12)

Standby mode with P

RXIN

= -45dBm to

P

RXIN

= 0dBm (Note 11)

70

Oscillator Buffer Output Level

-12

dBm

Oscillator Pulling kHz

PARAMETER

MIN TYP MAX

UNITSCONDITIONS

TA= T

MIN

to T

MAX

TA= +25°C

OSCILLATOR AND PRESCALER

DIV1 = 2.4V, ZL= 50Ω

(Note 4)

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

_______________________________________________________________________________________

5

24

28
26

34
32
30

40
38
36

42

-40 0 20-20 40 60 80 100

RECEIVER SUPPLY CURRENT

vs. TEMPERATURE

MAX2440/1/2-01

TEMPERATURE (°C)

I

CC

(mA)

VCC = 2.7V

PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT

VCC = 3.3V

VCC = 4.8V

0

1.0

0.5

2.5

2.0

1.5

4.0

3.5

3.0

4.5

-40 0 20-20 40 60 80 100

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

MAX2440/1/2-02

TEMPERATURE (°C)

I

CC

(µA)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

VCOON = GND
RXON = GND

25
20
15
10

5
0

-5

-10

-15

-20
0 0.5 1.0 1.5 2.0

RECEIVER GAIN vs. LNAGAIN

MAX2440/1/2-03

LNAGAIN VOLTAGE (V)

RECEIVER GAIN (dB)

ADJUSTABLE

GAIN

MAX
GAIN

LNA

PARTIALLY

BIASED

LNA
OFF

AVOID

THIS

REGION

18

22

20

26

24

-40 0 20-20 40 60 80 100

MAX2440

RECEIVER GAIN vs. TEMPERATURE

MAX2440/1/2-06

TEMPERATURE (°C)

RECEIVER GAIN (dB)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

LNAGAIN = V

CC

-20

-15

-10

-5

0

5

0 0.5 1.0 1.5 2.0

RECEIVER INPUT IP3 vs. V

LNAGAIN

MAX2440/1/2-04

LNAGAIN VOLTAGE (V)

IIP3 (dBm)

ADJUSTABLE

GAIN

AVOID

THIS

REGION

MAX
GAIN

LNA

PARTIALLY

BIASED

LNA
OFF

0

5

15
10

25
20

30

40
35

0 0.5 1.0 1.5 2.0

RECEIVER NOISE FIGURE

vs. LNAGAIN

MAX2440/1/2-05

LNAGAIN VOLTAGE (V)

NOISE FIGURE (dB)

ADJUSTABLE

GAIN

AVOID

THIS

REGION

MAX

GAIN

LNA

PARTIALLY

BIASED

LNA
OFF

DIV1 = V

CC

3.0

4.0

3.5

5.0

5.5

4.5

-40 0 20-20 40 60 80 100

RECEIVER NOISE FIGURE vs.

TEMPERATURE AND SUPPLY VOLTAGE

MAX2440/1/2-07

TEMPERATURE (°C)

NOISE FIGURE (dB)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

LNAGAIN = V

CC

DIV1 = V

CC

-20

-16

-18

-8

-10

-6

-12

-14

-40 0 20-20 40 60 80 100

RECEIVER INPUT IP3

vs. TEMPERATURE

MAX2440/1/2-08

TEMPERATURE (°C)

IIP3 (dBm)

V

LNAGAIN

= 1V

V

LNAGAIN

= 2V

Typical Operating Characteristics

(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f

RXIN

= 915MHz; P

RXIN

= -35dBm; V

LNAGAIN

= 2V; V

VCOON

= 2.4V; RXON = VCC; MOD = DIV1 = PREGND = GND; TA= +25°C;

unless otherwise noted.)

-9

-8

-4

-5

-3

-6

-7

-40 0 20-20 40 60 80

MAX2440

RXOUT 1dB COMPRESSION POINT

vs. TEMPERATURE

MAX2440/1/2-9

TEMPERATURE (°C)

1dB COMPRESSION POINT (dBm)

VCC = 2.7V

VCC = 4.8V

VCC = 3.3V

550
500

0

1 1k 10k100 100k

PRESCALER OUTPUT LEVEL

vs. LOAD RESISTANCE

100

50

MAX2440/1/2-13

LOAD RESISTANCE (Ω)

PRESCALER OUTPUT LEVEL (mVp-p)

200
150

350
300
250

450
400

LOAD IS PLOTTED RESISTANCE
IN PARALLEL WITH A 10pF
OSCILLOSCOPE PROBE
(÷ 64/65 MODE)

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f

RXIN

= 915MHz; P

RXIN

= -35dBm; V

LNAGAIN

= 2V; V

VCOON

= 2.4V; RXON = VCC; MOD = DIV1 = PREGND = GND; TA= +25°C;

unless otherwise noted.)

-20

10

-10

0

30
20

50
40

60

0 400 800 1200 1600 2000

RECEIVER IMAGE REJECTION

vs. RF FREQUENCY

MAX2440/1/2-10

RF FREQUENCY (MHz)

IMAGE REJECTION (dB)

RXON = V

CC

40

0

1 100010010

RECEIVER IMAGE REJECTION

vs. IF FREQUENCY

20
15
10

5

30
25

35

MAX2440/1/2-11

IF FREQUENCY (MHz)

IMAGE REJECTION (dB)

MAX2440

MAX2441

MAX2442

0

25

30

15

20

10

5

35

40

45

50

-0

-60

-40

-20

-80

-100

800600 1000 1200 1400

RXIN INPUT IMPEDANCE

vs. FREQUENCY

MAX2440/1/2-12

FREQUENCY (MHz)

REAL IMPEDANCE (Ω)

REAL

IMAGINARY

IMAGINARY IMPEDANCE (Ω)

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

_______________________________________________________________________________________ 7

Pin Description

DIV118

Driving DIV1 with a logic high disables the divide-by-64/65 prescaler and connects the PREOUT pin
directly to an oscillator buffer amplifier, which outputs -8dBm into a 50Ω load. Tie DIV1 low for divide-by­64/65 operation. Pull this pin low when in shutdown to minimize off current.

RXON

VCOON

MOD

16

Driving RXON with a logic high enables the LNA, receive mixer, and IF output buffer. VCOON must also
be high.

17

Driving VCOON with a logic high turns on the VCO, phase shifters, VCO buffers, and prescaler. The
prescaler can be selectively disabled by floating the PREGND pin.

19

Modulus Control for the Divide-by-64/65 Prescaler: high = divide-by-64, low = divide-by-65. Note that
the DIV1 pin must be at logic low when using the prescaler mode.

PREGND

PREOUT

20

V

CC

11

Supply Voltage Input for Signal-Path Blocks, except LNA. Bypass with a 47pF low-inductance capacitor
and 0.01µF to GND (pin 8 recommended).

GND8 Ground Connection for Signal-Path Blocks, except LNA. Connect directly to ground plane.

NAME

V

CC

CAP1

RXOUT

GND7 Ground Connection for Receive Low-Noise Amplifier. Connect directly to ground plane using multiple vias.

LNAGAIN10

Low-Noise Amplifier Gain-Control Input. Drive this pin high for maximum gain. When LNAGAIN is pulled
low, the LNA is capacitively bypassed and the supply current is reduced by 4.5mA. This pin can also be
driven with an analog voltage to adjust the LNA gain in intermediate states. Refer to the Receiver Gain
vs. LNAGAIN Voltage graph in the

Typical Operating Characteristics,

as well as Table 1.

PIN FUNCTION

1

Supply-Voltage Input for Master Bias Cell. Bypass with a 47pF low-inductance capacitor and 0.1µF to
GND (pin 28 recommended).

2

Receive Bias Compensation Pin. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND.
Do not make any other connections to this pin.

3 Single-Ended, 330Ω IF Output. AC couple to this pin.

Ground connection for the Prescaler. Tie PREGND to ground for normal operation. Leave floating to
disable the prescaler and the output buffer. Tie MOD and DIV1 to ground and leave PREOUT floating
when disabling the prescaler.

21

Prescaler/Oscillator Buffer Output. In divide-by-64/65 mode (DIV1 = low), the output level is 500mVp-p
into a high-impedance load. In divide-by-1 mode (DIV1 = high), this output delivers -8dBm into a 50Ω
load. AC couple to this pin.

GND

RXIN

V

CC

4, 9,

12–15

Ground Connection

5

Receiver RF Input, single-ended. The input match shown in Figure 1 maintains an input VSWR of better
than 2:1 from 902MHz to 928MHz.

6

Supply Voltage Input for Receive Low-Noise Amplifier. Bypass with a 47pF low-inductance capacitor to
GND (pin 7 recommended).

V

CC

22

Supply-Voltage Input for Prescaler. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND
(pin 20 recommended).

V

CC

23

Supply-Voltage Input for VCO and Phase Shifters. Bypass with a 47pF low-inductance capacitor to GND
(pin 26 recommended).

TANK

24

Differential Oscillator Tank Port. See

Applications Information

for information on tank circuits or on using

an external oscillator.

TANK25

Differential Oscillator Tank Port. See

Applications Information

for information on tank circuits or on using

an external oscillator.

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

8 _______________________________________________________________________________________

Pin Description (continued)

Ground Connection for VCO and Phase Shifters26 GND
Ground (substrate)27 GND
Ground Connection for Master Bias Cell28 GND

FUNCTIONPIN NAME

V

CC

V

CC

17
16
15

18

19

21

1000pF

VARACTOR:
ALPHA SMV1299-004
OR EQUIVALENT

RECEIVE IF OUTPUT (330Ω)

SEE

APPLICATIONS INFORMATION

SECTION

L3: COILCRAFT 0805HS-060TMBC

27

23

26

3

12

20

22

1

28

RECEIVE

RF INPUT

5

9

7

6

0.01µF

47pF

V

CCVCC

0.1µF

V

CC

V

CC

2

47pF0.1µF

8.2nH

12nH

47pF

47pF

47pF

8

11

0.01µF

47pF

0.01µF
MAX2440

MAX2441
MAX2442

6.8

6.8

6.8

L3

(nH)

PART

VCO TANK COMPONENTS FOR

915MHz TYPICAL RF

C26
(pF)

C2, C3

(pF)

2.0

1.5

1.5

2.0

2.7

2.0

47pF

14

RXIN

GND

GND

V

CC

V

CC

GND

GND

13

GND

4

GND

GND

CAP1

V

CC

V

CC

GND

RXON

VCOON

DIV1

MOD

PREOUT

RXON

VCOON

DIV1

MOD

TO PLL

GND

RXOUT

GND

100nH

GND

PREGND

47pF

V

CC

24

25

VCO
ADJUST

C3

1k

47k

47pF

1k

C2

10Ω

10Ω

V

CC

L3 C26

TANK

LNAGAIN

LNAGAIN

10

MAX2440
MAX2441
MAX2442

TANK

Figure 1. Typical Operating Circuit

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

_______________________________________________________________________________________ 9

Detailed Description

The following sections describe each of the blocks
shown in the

Functional Diagram.

Receiver

The MAX2440/MAX2441/MAX2442’s receive path con­sists of a 900MHz low-noise amplifier, an image-reject
mixer, and an IF buffer amplifier.

The LNA’s gain and biasing are adjustable via the
LNAGAIN pin. Proper operation of this pin can provide
optimum performance over a wide range of signal lev­els. The LNA can be placed in four modes by applying
a DC voltage on the LNAGAIN pin. See Table 1, as well
as the relevant

Typical Operating Characteristics

plots.

At low LNAGAIN voltages, the LNA is shut off, and the
input signal capacitively couples directly into the mixer
to provide maximum linearity for large-signal operation
(receiver close to transmitter). As the LNAGAIN voltage
is raised, the LNA begins to turn on. Between 0.5V and
1V at LNAGAIN, the LNA is partially biased and
behaves like a Class C amplifier. Avoid this operating
mode for applications where linearity is a concern. As
the LNAGAIN voltage reaches 1V, the LNA is fully
biased into Class A mode, and the gain is monotonical­ly adjustable at LNAGAIN voltages above 1V. See the
Receiver Gain, Receiver IP3, and Receiver Noise
Figure vs. LNAGAIN plots in the

Typical Operating

Characteristics

for more information.

The downconverter is implemented using an image­reject mixer consisting of an input buffer with two out­puts, each of which is fed to a double-balanced mixer.
The local-oscillator (LO) port of each mixer is driven
from a quadrature LO. The LO is generated from an on­chip oscillator and an external tank circuit. Its signal is
buffered and split into phase shifters, which provide
90° of phase shift across their outputs. This pair of LO
signals is fed to the mixers. The mixers’ outputs are
then passed through a second pair of phase shifters,
which provide a 90° phase shift across their outputs. The

resulting mixer outputs are then summed together. The
final phase relationship is such that the desired signal is
reinforced and the image signal is canceled. The down­converter mixer output appears on the RXOUT pin, a
single-ended 330

Ωoutput.

Phase Shifters

MAX2440/MAX2441/MAX2442 devices use passive
networks to provide quadrature phase shifting for the
receive IF and LO signals. Because these networks are
frequency selective, proper part selection is important.
Image rejection degrades as the IF and RF move away
from the designed optimum frequencies. Refer to the

Selector Guide

on the front page of this data sheet.

Local Oscillator (LO)

The on-chip LO is formed by an emitter-coupled differ­ential pair. An external LC resonant tank sets the oscil­lation frequency. A varactor diode is typically used to
create a voltage-controlled oscillator (VCO). See the

Applications Information

section and Figure 2 for an

example VCO tank circuit.
The LO may be overdriven in applications where an

external signal is available. The external LO signal
should be about 0dBm from 50Ω, and should be AC
coupled into either the TANK or TANK pin. Both TANK
and TANK require pull-up resistors to VCC. See the

Applications Information

section and Figure 3 for

details.
The local oscillator resists LO pulling caused by changes

in load impedance that occur as the part is switched
from standby mode. The amount of LO pulling will be
affected if there is power at the RXIN port due to imper­fect isolation in an external transmit/receive (T/R) switch.

Prescaler

The on-chip prescaler can be used in two different
modes: as a dual-modulus divide-by-64/65, or as oscil­lator buffer amplifier. The DIV1 pin controls this func­tion. When DIV1 is low, the prescaler is in dual-modulus
divide-by-64/65 mode; when it is high, the prescaler is
disabled and the oscillator buffer amplifier is enabled.
The buffer typically outputs -8dBm into a 50Ω load. To
minimize shutdown supply current, pull the DIV1 pin
low when in shutdown mode.

In divide-by-64/65 mode, the division ratio is controlled
by the MOD pin. When MOD is high, the prescaler is in
divide-by-64 mode; when it is low, it divides the LO fre­quency by 65. The DIV1 pin must be at a logic low in
this mode.

LNA partially biased. Avoid this mode—
the LNA operates in a Class C manner

LNA capacitively bypassed, minimum
gain, maximum IP3

MODE

LNA at maximum gain (remains monotonic)

LNA gain is monotonically adjustable

1.5 < V ≤ V

CC

1.0 < V ≤ 1.5

0.5 < V < 1.0

0 < V ≤ 0.5

LNAGAIN

VOLTAGE (V)

Table 1. LNA Modes

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

10 ______________________________________________________________________________________

To disable the prescaler entirely, leave PREGND and
PREOUT floating. Also tie the MOD and DIV1 pins to
GND. Disabling the prescaler does not affect operation
of the VCO stage.

Power Management

MAX2440/MAX2441/MAX2442 supports three different
power-management features to conserve battery life.
The VCO section has its own control pin (VCOON),
which also serves as a master bias pin. When VCOON is
high, the LO, quadrature LO phase shifters, and
prescaler or LO buffer are all enabled. The VCO can be
powered up prior to receiving to allow it to stabilize. With
VCOON high, bringing RXON high enables the receive
path, which consists of the LNA, image-reject mixers,
and IF output buffer. When this pin is low, the receive
path is inactive.

To disable all chip functions and reduce the supply
current to typically less than 0.5µA, pull VCOON, DIV1,
MOD, and RXON low.

Applications Information

Oscillator Tank

The on-chip oscillator requires a parallel-resonant tank
circuit connected across TANK and TANK. Figure 2
shows an example of an oscillator tank circuit. It typically
oscillates between 902MHz + IF and 928MHz + IF with a
control voltage between 0 and 3.3V. Inductor L4 pro­vides DC bias to the tank ports. L3 and the series combi­nation of capacitors C2, C3, and both halves of the
varactor diode capacitances set the resonant frequency
as follows:

where CD1is the capacitance of one varactor diode.
Choose the tank components according to your appli-

cation needs, such as phase-noise requirements, tun­ing range, and VCO gain. Higher-Q inductors yield
lower phase noise but are more likely to produce a sec­ond-harmonic oscillation mode. Air-core spring induc­tors provide high Q, but radiate more than chip
inductors. It may be necessary to shield the tank circuit
for optimal isolation of the LO to other circuitry. R6 and
R7 are 5Ω to 10Ω resistors that reduce the Q of para­sitic resonances due to package inductance.

Oscillator-Tank PC Board Layout

The parasitic PC board capacitance, as well as PCB
trace inductance and package inductance, can affect
oscillation frequency, so be careful in laying out the PC
board for the oscillator tank. Keep the tank layout as
symmetrical, tightly packed, and close to the device as
possible to minimize LO feedthrough. When using a PC
board with a ground plane, a cut-out in the ground
plane (and any other planes) below the oscillator tank
will reduce parasitic capacitance.

Using an External Oscillator

If an external 50Ω LO signal source is available, it can
be used as an input to the TANK or TANK pin in place
of the on-chip oscillator (Figure 3). The oscillator signal
is AC coupled into the TANK pin and should have a
level of about 0dBm from a 50Ω source. For proper
biasing of the oscillator input stage, TANK and TANK
must be pulled up to the VCCsupply via 50Ω resistors.

If a differential LO source such as the MAX2620 is
available, AC couple the inverting output into TANK.

C =

1

1

C2

EFF

+ +











+

132

26

1

C C

C

D

f =

1

2 L3 C

r

EFF

π

( )( )

MAX2440
MAX2441
MAX2442

TANK

L3

C26

L4

100nH

R5
1k

R4
1k

D1 = ALPHA SMV1299-004

SEE FIGURE 1 FOR C2, C3, C26, AND L3 COMPONENT VALUES.

1/2 D1

1/2 D1

C1
47pF

VCO_CTRL

R7

10Ω

R6

10Ω

C3

R8

47k

C2

V

CC

TANK

Figure 2. Oscillator Tank Schematic, Using the On-Chip VCO

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

______________________________________________________________________________________ 11

900MHz Image-Reject Receivers

MAX2440/MAX2441/MAX2442

Functional Diagram

MAX2440
MAX2441
MAX2442

TANK

50Ω

50Ω

EXT LO

EXTERNAL LO LEVEL IS
0dBm FROM A 50Ω
SOURCE.

V

CC

C

BLOCK

0.01µF

V

CC

TANK

RXON

CAP1

RXIN

LNAGAIN

90°

90°0°

Σ

MAX2440
MAX2441
MAX2442

PHASE

SHIFTER

÷1/64/65

BIAS

RXOUT

DIV1
MOD

PREOUT
PREGND

TANK

TANK
VCOON

0°

Figure 3. Using an External Local Oscillator

Chip Information

TRANSISTOR COUNT: 2802

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.

12

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

© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

Package Information

SSOP.EPS