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General Description

The MAX2685’s low-noise amplifier (LNA) and down-

converter 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 linear-

ity 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 opera-

tion 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 16-

pin QSOP package.

Applications

Cellular/Cordless Phones

900MHz ISM-Band Radios

Wireless Data

868MHz European ISM Band

Features

o 800MHz to 1000MHz RF Frequency Range

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

o Integrated LNA + Mixer + LO Buffer

o Logic-Controlled LNA Bypass Switch Reduces

Supply Current

o LNA Performance (High/Low Gain)

Gain: +15dB/-12dB

NF: 1.4dB/12dB

Input IP3: -4dBm/+16dBm

o Mixer Performance (High/Low Gain)

Gain: 6dB/4.6dB

NF: 13dB/12dB

Input IP3: +7dBm/-1.5dBm

o Supply Current

8.5mA (High Gain)

3.8mA (Low Gain)

o <0.1µA Supply Current in Shutdown Mode

o 0.8µs Receiver Enable Time

Low-Cost, 900MHz, Low-Noise Amplifier

and Downconverter Mixer

________________________________________________________________

Maxim Integrated Products

1

IFOUT+

IFOUT-

MAX2685

LNAIN

GAIN

LNA

LO

LNAOUT MIXIN

LNA BYPASS

LO

BUFFER

MIXER

SHDN

POWER

MANAGEMENT

GND

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

LNAOUT

GND

MIXIN

GND

GND

IFOUT+

IFOUT-

TOP VIEW

MAX2685

QSOP

LNAIN

SHDN

GAIN

GND

GND

LO

GND

Functional Diagram

19-1493; Rev 0; 7/99

PART

MAX2685EEE

-40°C to +85°C

TEMP. RANGE

PIN-PACKAGE

16 QSOP

EVALUATION

KIT MANUAL

FOLLOWS

DATA

SHEET

Pin Configuration

Ordering Information