Rainbow Electronics MAX2685 User Manual

General Description

The MAX2685’s low-noise amplifier (LNA) and down­converter mixer comprise the major blocks of an RF
front-end receiver. Optimized for 900MHz operation,
the device’s low noise figure, high gain, and high linear­ity make it ideal for cellular, cordless, and wireless data
applications. A low supply current of 8.5mA (high-gain
mode) and 3.8mA (low-gain mode) plus a low operating
supply voltage range of +2.7V to +5.5V make it suitable
for use in 3-cell NiCd or 1-cell lithium-ion (Li+) battery
applications. A low-power shutdown mode further
extends battery life by reducing supply current below

0.1µA.

The MAX2685 includes an LNA, LNA bypass switch,
downconverter mixer, and local-oscillator (LO) buffer.
The LNA has a low noise figure of 1.4dB, a high gain of
15dB, and an input third-order intercept point (IP3) of

-4dBm. The mixer has a noise figure of 13dB, a gain of
6dB, and an input IP3 of +7dBm. In addition, an LNA
bypass switch allows two levels of gain, reducing
power consumption when high gain is not needed.

The downconverter mixer has a single-ended RF input
port and differential IF output ports. Differential opera­tion of the IF ports offers improved even-order harmonic
rejection and increased immunity to noise. An LO buffer
allows the LO port to be driven with only -8dBm of LO
power. The MAX2685 is offered in a space-saving 16­pin QSOP package.

Applications

Cellular/Cordless Phones 900MHz ISM-Band Radios

Wireless Data 868MHz European ISM Band

Features

♦ 800MHz to 1000MHz RF Frequency Range

♦ +2.7V to +5.5V Single-Supply Operation

♦ Integrated LNA + Mixer + LO Buffer

♦ Logic-Controlled LNA Bypass Switch Reduces

Supply Current

♦ LNA Performance (High/Low Gain)

Gain: +15dB/-12dB
NF: 1.4dB/12dB
Input IP3: -4dBm/+16dBm

♦ Mixer Performance (High/Low Gain)

Gain: 6dB/4.6dB
NF: 13dB/12dB
Input IP3: +7dBm/-1.5dBm

♦ Supply Current

8.5mA (High Gain)

3.8mA (Low Gain)

♦ <0.1µA Supply Current in Shutdown Mode

♦ 0.8µs Receiver Enable Time

MAX2685

Low-Cost, 900MHz, Low-Noise Amplifier

and Downconverter Mixer

________________________________________________________________ Maxim Integrated Products 1

Functional Diagram

19-1493; Rev 1; 12/00

PART

MAX2685EEE -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 QSOP

EVALUATION KIT

AVAILABLE

Pin Configuration

Ordering Information

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.

MIXIN

LNAOUT

LNA

LNA BYPASS

MAX2685

POWER

MIXER

LO

BUFFER

LO

TOP VIEW

1

GND

2

LNAIN

3

GND

4

GAIN

5

V

CC

6

SHDN

7

LO

8

GND

MAX2685

QSOP

16

15

14

13

12

11

10

9

LNAOUT

V

CC

GND

MIXIN

GND

GND

IFOUT+

IFOUT-

LNAIN

GAIN

V

CC

SHDN

GND

MANAGEMENT

IFOUT+

IFOUT-

MAX2685

Low-Cost, 900MHz, Low-Noise Amplifier
and Downconverter Mixer

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(VCC= +2.7V to +5.5V, V

SHDN

= +2V, V

GAIN

= +2V, LNAIN = LNAOUT = MIXIN = LO = unconnected, IFOUT+ = IFOUT- = VCC, T

A

= -40°C to +85°C. Typical values are at TA= +25°C and VCC= +3V, unless otherwise noted.)

AC ELECTRICAL CHARACTERISTICS

(MAX2685 EV kit, VCC= V

SHDN

= +3V, f

LNAIN

= f

MIXIN

= 880MHz, fLO= 960MHz, P

LNAIN

= -30dBm, PLO= -8dBm, P

MIXIN

= -25dBm,

differential IFOUT operation, Z

o

= 50Ω, TA= +25°C, 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.

VCCto GND..............................................................-0.3V to +6V

LNAIN Input Power (50Ω source)...................................+10dBm

LO Input Power (50Ω source) ........................................+10dBm

MIXIN Input Power (50Ω source) ...................................+10dBm

IFOUT+, IFOUT- to GND ..........................................-0.3V to +6V

LNAOUT to GND ......................................................-0.3V to +6V

GAIN, SHDN to GND..................................-0.3V to (V

CC

+ 0.3V)

Continuous Power Dissipation (T

A

= +70°C)

16-Pin QSOP (derate 8.3mW/°C above +70°C)............667mW

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

Operating Temperature Range ...........................-40°C to +85°C

Storage Temperature Range .............................-65°C to +150°C

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

SHDN = GND (Note 1)

GAIN = V

CC

(Note 1)

GAIN, SHDN
GAIN, SHDN

V

SHDN

= V

GAIN

= 0 to 5.5V (Note 1)

CONDITIONS

µA0.1 1.0Shutdown Supply Current

8.5 14.1

V2.7 5.5Supply Voltage Range

V2.0Logic Input Voltage High

V0.5Logic Input Voltage Low

µA±0.01 ±1Logic Input Current

UNITSMIN TYP MAXPARAMETER

GAIN = GND (Note 1)

mA

3.8 6.4

Operating Supply Current

GAIN = GND (Note 1)

dB

-14 -12 -10.3

GAIN = VCC, TA= T

MIN

to T

MAX

(Note 3)

LNA Gain

GAIN = V

CC

(Note 1)

GAIN = V

CC

GAIN = GND

GAIN = V

CC

CONDITIONS

dB0.9 1.6LNA Gain Variation over Temperature

13 15 16.2

1.4
dB

12.2

LNA Noise Figure

-18.4LNA Input 1dB Compression

UNITSMIN TYP MAXPARAMETER

MHz800 1000RF Frequency Range (Note 2)

GAIN = V

CC

GAIN = GND

dBm

-18.6
dB

-11.3

LNAOUT Port Return Loss

MHz800 1000RF Frequency Range (Note 2)

GAIN = GND (Note 1)

dB

2.5 4.6 6.0

Mixer Conversion Gain

GAIN = V

CC

(Note 1) 4.7 6.1 7.0

GAIN = V

CC

(Note 4)

GAIN = GND (Note 5)

-4.1
dBm

+16.2

LNA Input IP3

LOW-NOISE AMPLIFIER (LNA)

DOWNCONVERTER MIXER

MAX2685

Low-Cost, 900MHz, Low-Noise Amplifier

and Downconverter Mixer

_______________________________________________________________________________________ 3

AC ELECTRICAL CHARACTERISTICS (continued)

(MAX2685 EV kit, VCC= V

SHDN

= +3V, f

LNAIN

= f

MIXIN

= 880MHz, fLO= 960MHz, P

LNAIN

= -30dBm, PLO= -8dBm, P

MIXIN

= -25dBm,

differential IFOUT operation, Z

o

= 50Ω, TA= +25°C, unless otherwise noted.)

Note 1: Performance at temperatures greater than or equal to +25°C are guaranteed by production test; performance at tempera-

tures less than +25°C are guaranteed by design and characterization.

Note 2: This is the recommended operating frequency range.
Note 3: Maximum and minimum limits are guaranteed by design and device characterization and are not production tested.
Note 4: Two tones at 880MHz and 880.1MHz, -30dBm per tone.
Note 5: Two tones at 880MHz and 880.1MHz, -10dBm per tone.
Note 6: Two tones at 880MHz and 880.1MHz, -25dBm per tone.
Note 7: Time from SHDN = high, until the cascaded receive gain is within 1dB of its final value. Measured with 47pF blocking

capacitors on LNAIN and LNAOUT. Matching network removed from IFOUT output.

Typical Operating Characteristics

(MAX2685 EV kit, VCC= V

SHDN

= +3V, f

LNAIN

= f

MIXIN

= 880MHz, fLO= 960MHz, P

LNAIN

= -30dBm, PLO= -8dBm, P

MIXIN

= -25dBm,

differential IFOUT operation, Z

o

= 50Ω, TA= +25°C, unless otherwise noted.)

0

3

2

1

4

5

6

7

8

9

10

2.5 3.53.0 4.0 4.5 5.0 5.5

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX2685 toc01

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

GAIN = HIGH

GAIN = LOW

TA = +85°C

TA = +25°C

TA = -40°C

TA = +85°C

TA = +25°C

TA = -40°C

0

3

2

1

4

5

6

7

8

9

10

2.5 3.53.0 4.0 4.5 5.0 5.5

SHUTDOWN SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX2685 toc02

SUPPLY VOLTAGE (V)

SHUTDOWN SUPPLY CURRENT (nA)

SHDN = GND

TA = -40°C

TA = +25°C

TA = +85°C

-15

-5

-10

5

0

15

10

20

2.5 3.5 4.03.0 4.5 5.0 5.5

LNA GAIN vs. SUPPLY VOLTAGE

MAX2685 toc03

SUPPLY VOLTAGE (V)

GAIN (dB)

GAIN = HIGH

GAIN = LOW

TA = +85°C

TA = +25°C

TA = -40°C

TA = +85°C

TA = +25°C

TA = -40°C

GAIN = GND

dB

12.1

Mixer Noise Figure (SSB)

GAIN = VCC, TA= T

MIN

to T

MAX

(Note 3)

GAIN = V

CC

dB12

Mixer Conversion Gain Variation over
Temperature

(Note 7)

dB

GAIN = V

CC

GAIN = GND

CONDITIONS

µs0.8Receiver Enable Time

13

7

dBm

-1.5

Mixer Input IP3 (Note 6)

11LO Port Return Loss

UNITSMIN TYP MAXPARAMETER

dB

SHDN = VCCor GND

53LO-to-LNAIN Isolation

dB

dB

28LNAOUT-to-MIXIN Isolation

31LO-to-MIXIN Isolation

OVERALL SYSTEM