Maxim MAX24276EAI, MAX2424EAI Datasheet

________________General Description

The MAX2424/MAX2426 highly integrated front-end ICs
provide the lowest cost solution for cordless and ISM­band radios operating in the 900MHz band. Both devices
incorporate a receive image-reject mixer (to reduce filter
cost) as well as a versatile transmit mixer. The devices
operate from a +2.7V to +4.8V single power supply,
allowing direct connection to a 3-cell battery stack.

The receive 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 (IIP3) of up to +2dBm.

The transmitter consists of a double-balanced mixer and
a power amplifier (PA) predriver that produces up to
0dBm (in some applications serving as the final power
stage). It can be used in a variety of configurations,
including BPSK modulation, direct VCO modulation, and
transmitter upconversion. For devices featuring trans­mit as well as receive image rejection, refer to the
MAX2420/MAX2421/MAX2422/MAX2460/MAX2463
data sheet.

The MAX2424/MAX2426 have 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. Four separate power­down inputs can be used for system power manage­ment, including a 0.5µA shutdown mode.

The MAX2424/MAX2426 come in a 28-pin SSOP pack­age.

________________________Applications

Cordless Phones

Wireless Telemetry

Wireless Networks

Spread-Spectrum Communications

Two-Way Paging

____________________________Features

♦ Receive Mixer with 35dB Image Rejection
♦ Adjustable-Gain LNA
♦ Up to +2dBm Combined Receiver Input IP3
♦ 4dB Combined Receiver Noise Figure
♦ Optimized for Common Receiver IF Frequencies:

10.7MHz (MAX2424)
70MHz (MAX2426)

♦ PA Predriver Provides up to 0dBm
♦ Low Current Consumption: 23mA Receive

20mA Transmit

9.5mA Oscillator

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

MAX2424/MAX2426

900MHz Image-Reject Receivers

with Transmit Mixer

________________________________________________________________

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

TXON

PREOUT

PREGND

MOD

DIV1

VCOON

RXON

CAP2

TXIN

TXIN

LNAGAIN

TXOUT

GND

GND

RXIN

GND

RXOUT

CAP1

SSOP

TOP VIEW

MAX2424
MAX2426

TANK

V

CC

V

CC

V

CC

V

CC

V

CC

___________________Pin Configuration

19-1350 Rev 2; 2/99

PART

MAX2424EAI

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

28 SSOP

_______________Ordering Information

Functional Diagram appears at end of data sheet.

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

MAX2426EAI

-40°C to +85°C 28 SSOP

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone].

MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

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

TXIN

= V

TXIN

= 2.3V, V

VCOON

= 2.4V, V

RXON

= V

TXON

=

V

MOD

= V

DIV1

= 0.45V, PREGND = GND, TA= -40°C to +85°C. Typicals 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.

Note 4: Calculated by measuring the combined transmit and oscillator supply current and subtracting the oscillator supply current.

V

CC

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

TXIN, TXIN Differential Voltage..............................................+2V

Voltage on TXOUT......................................-0.3V to (V

CC

+ 1.0V)

Voltage on LNAGAIN, TXON, RXON, VCOON,

DIV1, MOD, TXIN, TXIN............................-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 ...........................-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 (Note 3) 23 36 mA

Prescaler Supply Current
(buffer mode) (Note 2)

5.4 8.5 mA

Oscillator Supply Current

Supply-Voltage Range 2.7 4.8 V

9.5 14 mA

Prescaler Supply Current
(÷ 64/65 mode) (Note 1)

4.2 6 mA

CONDITIONS

V

RXON

= 2.4V, PREGND = unconnected

V

DIV1

= 2.4V

PREGND = unconnected

Digital Input Voltage Low 0.45 V

Shutdown Supply Current

0.5

RXON, TXON, DIV1, VCOON, MOD

VCOON = RXON = TXON
= MOD = DIV1 = GND

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

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

10

µA

TA= +25°C
TA= -40°C to +85°C

Transmitter Supply Current (Note 4) 20 32 mA

V

RXON

= 0.45V, V

TXON

= 2.4V,

PREGND = unconnected

AC ELECTRICAL CHARACTERISTICS

(MAX2424/MAX2426 EV kit, VCC= +3.3V, f

RXIN

= 915MHz, P

RXIN

= -35dBm, V

TXIN

= V

TXIN

= 2.3V (DC bias), V

TXIN

= 250mVp-p,

f

TXIN

= 1MHz, V

LNAGAIN

= 2V, V

VCOON

= 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)

MAX2424/MAX2426

900MHz Image-Reject Receiver

with Transmit Mixer

_______________________________________________________________________________________ 3

(Note 11)

MAX2424 (Notes 5, 6)

TA= T

MIN

to T

MAX

(Note 5)

TA= +25°C

(Notes 5, 6)

(Notes 5, 10)

(Note 9)

Receiver on or off

LNAGAIN = GND (Note 7)

V

LNAGAIN

= 1V (Note 7)

V

LNAGAIN

= 1V (Notes 5, 8)

LNAGAIN = V

CC

(Notes 5, 8)

V

LNAGAIN

= VCC,

TA= -40°C to +85°C (Notes 5, 7)

MAX2426 (Notes 5, 6)

V

LNAGAIN

= VCC,

TA= +25°C (Note 7)

V

LNAGAIN

= 1V (Notes 5, 7)

LNAGAIN = V

CC

(Notes 5, 7)

CONDITIONS

dBc30Carrier Suppression

dBm3.5Output Third-Order Intercept (OIP3)

dBm-0.5Output 1dB Compression

-10 -4.5

dBm

-9.5 -7 -5

Output Power

MHz125Baseband 3dB Bandwidth

MHz800 1000Output Frequency Range

ns500Receiver Turn-On Time

dBm-60LO to RXIN Leakage

-8

dB

-19 -17

Input Third-Order Intercept
(IIP3)

12

dB

45

Noise Figure

MHz

8.5 10.7 12.5

MHz800 1000Input Frequency Range

-16

12

18 24

19 25

55 70 85

IF Frequency Range

dB26 35Image Frequency Rejection

dB

20 22 24.5

Conversion Power Gain

19 21 23.5

UNITSMIN TYP MAXPARAMETER

MAX2424
MAX2426
MAX2424
MAX2426

V

LNAGAIN

= 1V

LNAGAIN = V

CC

-18

dBm

-26

Input 1dB Compression

(Note 12) ns220Transmitter Turn-On Time

dBm/Hz-140Output Noise Density

RECEIVER (V

RXON

= 2.4V, fLO= 925.7MHz (MAX2424), fLO= 985MHz (MAX2426))

TRANSMITTER (V

TXON

= 2.4V, fLO= 915MHz)

V

DIV1

= 2.4V, ZL= 50Ω,

MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

4 _______________________________________________________________________________________

AC ELECTRICAL CHARACTERISTICS (continued)

(MAX2424/MAX2426 EV kit, VCC= +3.3V, f

RXIN

= 915MHz, P

RXIN

= -35dBm, V

TXIN

= V

TXIN

= 2.3V (DC bias), V

TXIN

= 250mVp-p,

f

TXIN

= 1MHz, V

LNAGAIN

= 2V, V

VCOON

= 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)

PARAMETER MIN TYP MAX UNITS

Oscillator Phase Noise

Oscillator Frequency Range 800 1100 MHz

82

dBc/Hz

(Note 5)

CONDITIONS

Note 5: Guaranteed by design and characterization.
Note 6: Image rejection typically falls to 30dBc at the frequency extremes.
Note 7: Refer to the

Typical Operating Characteristics

for a plot showing Receiver Gain vs. LNAGAIN Voltage, Input IP3 vs.

LNAGAIN Voltage, and Noise Figure vs. LNAGAIN Voltage.

Note 8: Two tones at P

RXIN

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

Note 9: Time delay from V

RXON

= 0.45V to V

RXON

= 2.4V transition to the time the output envelope reaches 90% of its final value.

Note 10: Output power typically falls to -10dBm at the frequency extremes.
Note 11: Two tones at V

TXIN

= 125mVp-p, f1 = 1.0MHz, and f2 = 1.2MHz.

Note 12: Time delay from V

TXON

= 0.45V to V

TXON

= 2.4V transition to the time the output envelope reaches 90% of its final value.

Note 13: Using tank components L3 = 5.0nH (Coilcraft A02T), C2 = C3 = C26 = 3.3pF, R6 = R7 = 10Ω.
Note 14: This approximates a typical application in which TXOUT is followed by an external PA and a T/R switch with finite isolation.
Note 15: Relative to the rising edge of PREOUT.

Prescaler Output Level

500 mVp-p

-11 -8

Required Modulus Setup Time
(Notes 5, 15)

10 ns

ZL= 100kΩ

| |

10pF

÷ 64/65 mode

Required Modulus Hold Time
(Notes 5, 15)

0 ns

÷ 64/65 mode

Oscillator Buffer Output Level
(Notes 5, 13)

-12

dBm

V

DIV1

= 2.4V,

ZL= 50Ω

10kHz offset (Note 13)

72

Standby to TX or Standby to RX

35

Oscillator Pulling

8

kHz

110

RX to TX with P

RXIN

=-45dBm (RX mode)

to P

RXIN

= 0dBm (TX mode) (Note 14)

MAX2424
MAX2426
MAX2424
MAX2426
MAX2424
MAX2426

70

TA= +25°C
TA= -40°C to +85°C

OSCILLATOR AND PRESCALER

MAX2424/MAX2426

900MHz Image-Reject Receiver

with Transmit Mixer

_______________________________________________________________________________________

5

28

32

30

38

36

34

42

40

24

26

-40 0 20-20 40 60 80

RECEIVER SUPPLY CURRENT

vs. TEMPERATURE

MAX2424/6-01

TEMPERATURE (°C)

I

CC

(mA)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

RXON = V

CC

PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT

37

35

33

31

29

27

25

23

21

39

-40 0 20-20 40 60 80

TRANSMITTER SUPPLY CURRENT

vs. TEMPERATURE

MAX2424/6-02

TEMPERATURE (°C)

I

CC

(mA)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

TXON = V

CC

PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT

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

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

MAX2424/6-03

TEMPERATURE (°C)

I

CC

(µA)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

VCOON = GND

25

20

15

10

5

0

-5

-10

-15

-20
0 0.5 1.0 1.5 2.0

RECEIVER GAIN vs. LNAGAIN

MAX2424/6-04

LNAGAIN VOLTAGE (V)

RECEIVER GAIN (dB)

ADJUSTABLE

GAIN

MAX
GAIN

LNA

PARTIALLY

BIASED

LNA
OFF

AVOID

THIS

REGION

RXON = V

CC

18

22

20

26

24

-40 0 20-20 40 60 80

MAX2424

RECEIVER GAIN vs. TEMPERATURE

MAX2424/6-07

TEMPERATURE (°C)

RECEIVER GAIN (dB)

VCC = 2.7V

VCC = 3.3V

VCC = 4.8V

LNAGAIN = V

CC

RXON = V

CC

-20

-15

-10

-5

0

5

0 0.5 1.0 1.5 2.0

RECEIVER INPUT IP3 vs. LNAGAIN

MAX2424/6-05

LNAGAIN VOLTAGE (V)

IIP3 (dBm)

ADJUSTABLE

GAIN

AVOID

THIS

REGION

MAX
GAIN

LNA

PARTIALLY

BIASED

LNA
OFF

RXON = V

CC

0

5

15

10

25

20

30

40

35

0 0.5 1.0 1.5 2.0

RECEIVER NOISE FIGURE

vs. LNAGAIN

MAX2424/6-06

LNAGAIN VOLTAGE (V)

NOISE FIGURE (dB)

ADJUSTABLE

GAIN

AVOID

THIS

REGION

MAX

GAIN

LNA

PARTIALLY

BIASED

LNA
OFF

RXON = V

CC

DIV1 = V

CC

3.0

4.0

3.5

5.0

5.5

4.5

-40 0 20-20 40 60 80

RECEIVER NOISE FIGURE vs.

TEMPERATURE AND SUPPLY VOLTAGE

MAX2424/6-08

TEMPERATURE (°C)

NOISE FIGURE (dB)

VCC = 3.3V

LNAGAIN = V

CC

RXON = V

CC

DIV1 = V

CC

VCC = 4.8V

V

CC

= 2.7V

-20

-16

-18

-8

-10

-6

-12

-14

-40 0 20-20 40 60 80

RECEIVER INPUT IP3

vs. TEMPERATURE

MAX2424/6-09

TEMPERATURE (°C)

IIP3 (dBm)

V

LNAGAIN

= 1V

RXON = V

CC

V

LNAGAIN

= 2V

__________________________________________Typical Operating Characteristics

(MAX2424/MAX2426 EV kit, VCC= +3.3V; f

LO(

RX)

= 925.7MHz (MAX2424), 985MHz (MAX2426); f

RXIN

= 915MHz, P

RXIN

=

-35dBm, f

LO(TX)

= 915MHz, V

TXIN

= V

TXIN

= 2.3V (DC bias), V

TXIN

= 250mVp-p, f

TXIN

= 1MHz, V

LNAGAIN

= 2V, V

VCOON

= 2.4V,

RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)

MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

6 _______________________________________________________________________________________

______________________________Typical Operating Characteristics (continued)

(MAX2424/MAX2426 EV kit, VCC= +3.3V; f

LO(

RX)

= 925.7MHz (MAX2424), 985MHz (MAX2426); f

RXIN

= 915MHz, P

RXIN

=

-35dBm, f

LO(TX)

= 915MHz, V

TXIN

= V

TXIN

= 2.3V (DC bias), V

TXIN

= 250mVp-p, f

TXIN

= 1MHz, V

LNAGAIN

= 2V, V

VCOON

= 2.4V,

RXON = TXON = 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

MAX2424/6-11

RF FREQUENCY (MHz)

IMAGE REJECTION (dB)

RXON = V

CC

-9

-8

-4

-5

-3

-6

-7

-40 0 20-20 40 60 80

MAX2424

RECEIVER OUTPUT 1dB

COMPRESSION POINT vs. TEMPERATURE

MAX2424/6-10

TEMPERATURE (°C)

1dB COMPRESSION POINT (dBm)

VCC = 2.7V

VCC = 4.8V

RXON = V

CC

VCC = 3.3V

0

10

20

30

5

15

25

35

40

1 10 100 1000

RECEIVER IMAGE REJECTION

vs. IF FREQUENCY

MAX2424/6-12

IF FREQUENCY (MHz)

IMAGE REJECTION (dB)

RXON = V

CC

MAX2424 MAX2426

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

MAX2424/6-13

FREQUENCY (MHz)

REAL IMPEDANCE (Ω)

IMAGINARY IMPEDANCE (Ω)

REAL

IMAGINARY

RXON = V

CC

-300

-200

-250

-50

-100

-150

0

50

100

150

800600 1000 1200 1400 1600 1800 2000

TXOUT OUTPUT IMPEDANCE

vs. FREQUENCY

MAX2424/6-16

FREQUENCY (MHz)

REAL OR IMAGINARY IMPEDANCE (Ω)

REAL

IMAGINARY

TXON = V

CC

5

-25

-15

-20

-5

-10

0

TRANSMITTER OUTPUT POWER

vs. INPUT VOLTAGE

MAX2424/6-14

INPUT VOLTAGE (mVp-p)

OUTPUT POWER (dBm)

10 100 1000

VCC = 2.7V

V

CC

= 4.8V

V

CC

= 3.3V

TXON = V

CC

-14

-2

-3

-4

-5

-6

-7

-8

-9

-10

-11

-12

-13

-40 0

20

-20

40 60 80

TRANSMITTER OUTPUT POWER

vs. TEMPERATURE

MAX2424/6-15

TEMPERATURE (°C)

OUTPUT POWER (dBm)

VCC = 2.7V

VCC = 4.8V

VCC = 3.3V

TXON = V

CC

-100

-80

-90

-60

-70

-40

-50

-30

-10

-20

0

910 912 913 914911 915 916 917 919918 920

TRANSMITTER OUTPUT SPECTRUM

MAX2424/6-17

FREQUENCY (MHz)

POWER (dBm)

DOUBLE-SIDE
BAND
FUNDAMENTAL

LO

TXON = V

CC

-7

-5

-6

-3

-4

0

-1

-2

1

-40 0-20 20 40 60 80

TRANSMITTER 1dB COMPRESSION POINT

vs. TEMPERATURE

MAX2424/6-18

TEMPERATURE (°C)

OUTPUT 1dB COMPRESSION (dBm)

VCC = 4.8V

VCC = 3.3V

VCC = 2.7V

TXON = V

CC

MAX2424/MAX2426

900MHz Image-Reject Receiver

with Transmit Mixer

_______________________________________________________________________________________

7

-36

3
0

-3

-6

-9

-12

-15

-18

-21

-24

-27

-30

-33

1 10 100 1000

TRANSMITTER BASEBAND

FREQUENCY RESPONSE

MAX2424/6-20

FREQUENCY (MHz)

TXOUT (dBc)

TXON = V

CC

-100

10

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

10 100 1000

POWER vs. TXIN VOLTAGE

MAX2424/6-19

TXIN VOLTAGE (mVp-p)

POWER (dBm)

TXON = V

CC

NOTE: TXIN IS TOTAL
VOLTAGE FOR TWO TONES
(PEAK-TO-PEAK)

FUNDAMENTAL

IM3 LEVEL

______________________________Typical Operating Characteristics (continued)

(MAX2424/MAX2426 EV kit, VCC= +3.3V; f

LO(

RX)

= 925.7MHz (MAX2424), 985MHz (MAX2426); f

RXIN

= 915MHz, P

RXIN

=

-35dBm, f

LO(TX)

= 915MHz, V

TXIN

= V

TXIN

= 2.3V (DC bias), V

TXIN

= 250mVp-p, f

TXIN

= 1MHz, V

LNAGAIN

= 2V, V

VCOON

= 2.4V,

RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)

______________________________________________________________Pin Description

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

6

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.

5

Ground Connection4

V

CC

RXIN

GND

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

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.

2

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

1

FUNCTIONPIN

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.

10

PA Predriver Output. See Figure 1 for an example matching network, which provides better than 2:1
VSWR from 902MHz to 928MHz.

9

LNAGAIN

TXOUT

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

7 GND

RXOUT

CAP1

V

CC

NAME

Ground Connection for Signal-Path Blocks, except LNA8 GND

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

11 V

CC

MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

8 _______________________________________________________________________________________

_________________________________________________Pin Description (continued)

FUNCTIONPIN NAME

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

14

Transmit Mixer’s Inverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port.
See Figure 1.

13

CAP2

TXIN

Transmit Mixer’s Noninverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input
port. See Figure 1.

12 TXIN

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.

21

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

20

PREOUT

PREGND

Modulus Control for the Divide-by-64/65 Prescaler. Drive MOD high for divide-by-64 mode. Drive MOD
low for divide-by-65 mode.

19

Drive VCOON with a logic high to turn on the VCO, phase shifters, VCO buffers, and prescaler. To dis­able the prescaler, leave the PREGND pin unconnected.

17

Drive RXON and VCOON with a logic high to enable the LNA, receive mixer, and IF output buffer.
See

Power Management

section.

16

MOD

VCOON

RXON

Drive TXON and VCOON with a logic high to enable the transmit IF variable-gain amplifier, upconverter
mixer, and PA predriver. See

Power Management

section.

15 TXON

Drive DIV1 with a logic high to disable the divide-by-64/65 prescaler and connect the PREOUT pin
directly to an oscillator buffer amplifier, which outputs -8dBm into a 50Ω load. Drive DIV1 low for divide­by-64/65 operation. Drive this pin low when in shutdown to minimize shutdown current.

18 DIV1

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

22 V

CC

Differential Oscillator Tank Port. See

Applications Information

for information on tank circuits or on using

an external oscillator.

24

TANK

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

23 V

CC

Differential Oscillator Tank Port. See

Applications Information

for information on tank circuits or on using

an external oscillator.

25 TANK

Ground Connection for VCO and Phase Shifters26 GND

Ground (substrate)27 GND

Ground Connection for Master Bias Cell28 GND

MAX2424/MAX2426

900MHz Image-Reject Receiver

with Transmit Mixer

_______________________________________________________________________________________ 9

V

CC

V

CC

17

16

15

18

19

21

1000pF

VARACTORS:
ALPHA SMV1299-004
OR EQUIVALENT

WHEN USING DIFFERENTIAL
SOURCE, REMOVE RESISTORS
AND REPLACE CAPACITORS WITH
SHORTS. FOR SINGLE-ENDED
SOURCE, DRIVE ONLY MODULATOR
INPUT. CHOOSE R

A

AND RB VALUES

AS SHOWN IN

TRANSMITTER

SECTION.

RECEIVE IF OUTPUT (330Ω)

27

23

26

3

20

22

1

28

RECEIVE

RF INPUT

TRANSMIT

RF OUTPUT

5

9

7

6

0.01µF

47pF

V

CCVCC

0.1µF

V

CC

V

CC

V

CC

2

47pF

47pF

0.1µF

8.2nH

12nH

22nH

18nH

47pF

47pF

47pF

8

11

0.01µF

47pF

0.01µF

VCO TANK COMPONENTS

FOR 915MHz RF FREQUENCY

47pF

14

0.01µF

47pF

RXIN

TXOUT

GND

V

CC

V

CC

GND

GND

CAP2

GND

CAP1

V

CC

V

CC

TXON

RXON

VCOON

DIV1

MOD

PREOUT

TXON

RXON

VCOON

DIV1

MOD

TO PLL

GND

RXOUT

100nH

GND

PREGND

47pF

24

25

VCO
ADJUST

C3

1k

47k

47pF

1k

C2

C26

R6

R7

V

CC

V

CC

R

A

R

B

10k

10k

L3

TANK

MODULATOR INPUT

12

0.01µF*

TXIN

MODULATOR INPUT

13

0.01µF*

TXIN

LNAGAIN

LNAGAIN

4

47pF

10

MAX2424
MAX2426

TANK

*

MAX2424

MAX2426

DEVICE

10

20

R6, R7

(Ω)

2.0

4.0

C26
(pF)

6.8

3.3

L3

(nH)

3.3

8.0

C2, C3

(pF)

Figure 1. Typical Operating Circuit

MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

10 ______________________________________________________________________________________

_______________Detailed Description

The following sections describe each of the functional
blocks shown in the

Functional Diagram.

Receiver

The MAX2424/MAX2426’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 provides optimum
performance over a wide range of signal levels. The LNA
has four modes determined by the DC voltage applied 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 mixer to
provide maximum linearity for large-signal operation
(receiver close to transmitter). As the LNAGAIN voltage
increases, the LNA turns 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 for LNA­GAIN voltages above 1V. See the receiver gain, IP3, and
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.
A quadrature LO drives the local-oscillator (LO) port of

each mixer. An on-chip oscillator and an external tank
circuit generates the LO. Its signal is buffered and split
into two phase shifters, which provide 90° of phase shift
across their outputs. This pair of LO signals is fed to the
mixers. The mixers’ outputs then pass 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 330Ω output.

Transmitter

The MAX2424/MAX2426 transmitter consists of a bal­anced mixer and a PA driver amplifier. The mixer inputs
are accessible via the TXIN and TXIN pins. An equiva­lent circuit for the TXIN and TXIN pins is shown in
Figure 2. Because TXIN and TXIN are linearly coupled
to the mixer stage, they can accept spectrally shaped
input signals. Typically, the mixer can be used to multi­ply the LO with a baseband signal, generating BPSK or
ASK modulation. Transmit upconversion can also be
implemented by applying a modulated IF signal to
these inputs. For applications requiring image rejection
on the transmitter, refer to the MAX2420/MAX2421/
MAX2422/MAX2460/MAX2463 data sheet.

Set the common-mode voltage at TXIN, TXIN to 2.3V by
selecting appropriate values for RAand RB(Figure 1). The
total series impedance of RAand RBshould be approxi­mately 100kΩ.

Frequency modulation (FM) is realized by modulating
the VCO tuning voltage. Apply the appropriate differen­tial and common-mode voltages to TXIN and TXIN to
control transmitter output power (Figure 3).

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

LNAGAIN

≤ V

CC

1.0 < V

LNAGAIN

≤ 1.5

0.5 < V

LNAGAIN

< 1.0

0 < V

LNAGAIN

≤ 0.5

LNAGAIN

VOLTAGE (V)

Table 1. LNA Modes

MAX2424
MAX2426

TXIN

2M

1.5µA

1.5µA

VMIXER INPUT

TXIN

Figure 2. TXIN, TXIN Equivalent Circuit

MAX2424/MAX2426

900MHz Image-Reject Receiver

with Transmit Mixer

______________________________________________________________________________________ 11

For example, if VCC= 3.3V and P

OUT

= -8dBm, choose
RT= 100kΩ for sufficient current through the divider, so
that bias currents for TXIN and TXIN have little effect
over temperature. Set V

TXIN

= 2.3V to satisfy common-

mode voltage range requirements at VCC= 3.3V.
Use the Transmit Output Power vs. Input Voltage graph

in the

Typical Operating Characteristics

to determine

the input voltage (in mVp-p) required to produce the
desired output. Divide this value by 2√2 and use it for
V

DIFF

. A -8dBm transmitter output requires 250mVp-p /

2√2 = 88.4mV.

V

TXIN

= 2.3V + 0.0884V = 2.3884V

RT= R1 + R2 + R3

Solve for resistors R1, R2, and R3 with the following
equations:

Since the transmit and receive sections typically require
different LO frequencies, it is not recommended to have
both transmit and receive active at the same time.

Phase Shifter

The MAX2424/MAX2426 uses passive networks to pro­vide quadrature phase shifting for the receive IF and LO
signals. Because these networks are frequency selec­tive, both the RF and IF frequency operating ranges are
limited. Image rejection degrades as the IF and RF
moves away from the designed optimum frequencies.
The MAX2424/MAX2426’s phase shifters are arranged
such that the LO frequency is higher than the RF carrier
frequency (high-side injection).

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 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 for details.

The local oscillator resists pulling caused by changes
in load impedance that occur as the part is switched
from standby mode, with just the oscillator running to
either transmit or receive mode. The amount of LO
pulling is affected if a signal is present at the RXIN port
in transmit mode. The most common cause of pulling is
imperfect isolation in an external transmit/
receive (T/R) switch. The

AC Electrical Characteristics

table contains specifications for this case as well.

Prescaler

The on-chip prescaler operates in two different modes:
as a dual-modulus divide-by-64/65, or as an 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 drive mode, the division ratio is con­trolled by the MOD pin. Drive MOD high to operate the
prescaler in divide-by-64 mode. Drive MOD and DIV1
low to operate the prescaler in divide-by-65 mode.

R3

V x R

V

R2 V – V x

R

V

R1 R – R2 – R3

T

CC

TXIN

T

CC

T

=

=

()

=

TXIN

TXIN

RT = R1 + R2 + R

3

V

DIFF

= V

TXIN

- V

TXIN

R1 i

R2

R3

2M

V

CC

1.5µA

TXIN

1.5µA

TXIN

MAX2424
MAX2426

Figure 3. Biasing TXIN and TXIN for FM

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

Power Management

The MAX2424/MAX2426 supports four different power­management 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. Stabilize VCO by powering it up
prior to transmitting or receiving. For transmit-to-receive
switching, the receiver and transmitter sections have
their own enable control inputs, RXON and TXON. 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. The TXON input enables the upcon­verter mixer and PA predriver. VCOON must be high for
the transmitter to operate. When TXON is low, the trans­mitter is off.

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

___________Applications Information

Oscillator Tank

The on-chip oscillator requires a parallel-resonant tank
circuit connected across TANK and TANK. Figure 4
shows an example of an oscillator tank circuit. Inductor
L4 provides DC bias to the tank ports. Inductor L3,
capacitor C26, and the series combination of capaci­tors C2, C3, and both halves of the varactor diode
capacitance set the resonant frequency as follows:

where CD1is the capacitance of one varactor diode.

Choose tank components according to your application
needs, such as phase-noise requirements, tuning
range, and VCO gain. High Q inductors such as air­core micro springs yield low phase noise. Use a low­tolerance inductor (L3) for predictable oscillation
frequency. Resistors R6 and R7 can be chosen from 0
to 20Ω to reduce the Q of parasitic resonance due to
series package inductance L

T

. Keep R6 and R7 as
small as possible to minimize phase noise, yet large
enough to ensure oscillator start-up in fundamental
mode. Oscillator start-up with be most critical with high
tuning bandwidth (low tank Q) and high temperature.
Capacitors C2 and C3 couple in the varactor. Light
coupling of the varactor is a way to reduce the effects
of high varactor tolerance and increase loaded Q. For a
wider tuning range, use larger values for C2 and C3 or
a varactor with a large capacitance ratio. Capacitor
C26 is used to trim the tank oscillator frequency. Larger
values for C26 will help negate the effect of stray PCB
capacitance and parasitic inductor capacitance (L3).
Choose a low-tolerance capacitor for C26.

C =

1

1C21

C32C

EFF

D1

++











+ C26

f =

1

2L3C

r

EFF

π

()

()











MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

12 ______________________________________________________________________________________

MAX2424
MAX2426

TANK

L3

6.8nH

L4

100nH

R5
1k

R4
1k

1/2 D1

1/2 D1

D1 = ALPHA SMV1299-004

SEE FIGURE 1 FOR R6, R7, C2, C3, C26, AND L3 COMPONENT VALUES.

C1
47pF

VCO_CTRL

R7

R6

C3

R8

47k

C2

C26

V

CC

TANK

Figure 4. Oscillator Tank Schematic Using the On-Chip VCO

For applications that require a wide tuning range and
low phase noise, a series-coupled resonant tank may
be required as shown in Figure 5. This tank will use the
package inductance in series with inductors L1, L2,
and capacitance of varactor D1 to set the net equiva­lent inductance which resonates in parallel with the
internal oscillator capacitance. Inductors L1 and L2
may be implemented as microstrip inductors, saving
component cost. Bias is provided to the tank port
through chokes L3 and L5. R1 and R3 should be cho­sen large enough to de-Q the parasitic resonance due
to L3 and L5 but small enough to minimize the voltage
drop across them due to bias current. Values for R1
and R3 should be kept between 0 and 50Ω. Proper
high frequency bypassing (C1) should be used for the
bias voltage to eliminate power supply noise from
entering the tank.

Oscillator Tank PC Board Layout

The parasitic PC board capacitance, as well as PCB
trace inductance and package inductance, 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
reduces 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 6). 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, pull up the TANK
and TANK pins to the VCCsupply via 50Ω resistors.

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

MAX2424/MAX2426

900MHz Image-Reject Receiver

with Transmit Mixer

______________________________________________________________________________________ 13

MAX2424

TANK

50Ω

50Ω

50Ω

47pF

50Ω

EXT LO

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

V

CC

47pF

V

CC

TANK

Figure 6. Using an External Local Oscillator

MAX2424
MAX2426

TANK

L1

L

T

L

T

L2

L3

L4

L5

R1

R2

R3

C

i

1/2 D1

1/2 D1

C1C2

V

CC

V

TUNE

TANK

Figure 5. Series-Coupled Resonant Tank for Wide Tuning Range and Low Phase Noise

MAX2424/MAX2426

900MHz Image-Reject Receiver
with Transmit Mixer

14 ______________________________________________________________________________________

_________________________________________________________Functional Diagram

RXON
TXON

CAP2

TXOUT

CAP1

RXIN

LNAGAIN

90°

90°0°

0°

Σ

MAX2424
MAX2426

PHASE

SHIFTER

÷ 1/64/65

BIAS

RXOUT

DIV1
MOD

PREOUT

PREGND

TANK

TANK

VCOON

TXIN

0°

TXIN

________________________________________________________Package Information

SSOP.EPS