19-1493; Rev 1; 12/00
Low-Cost, 900MHz, Low-Noise Amplifier
and Downconverter Mixer
General Description
Features
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.
ꢀ 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
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.
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
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.
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
Applications
MAX2685EEE
-40°C to +85°C
16 QSOP
Cellular/Cordless Phones
Wireless Data
900MHz ISM-Band Radios
868MHz European ISM Band
Functional Diagram
Pin Configuration
LNAOUT MIXIN
TOP VIEW
LNA
MIXER
1
16
GND
LNAOUT
IFOUT+
IFOUT-
2
15
LNAIN
GAIN
LNAIN
V
CC
3
14
13
12
11
10
9
GND
GND
LNA BYPASS
4
GAIN
MIXIN
GND
5
V
CC
MAX2685
6
7
8
MAX2685
GND
SHDN
LO
LO
BUFFER
V
CC
POWER
MANAGEMENT
IFOUT+
IFOUT-
SHDN
GND
GND
QSOP
LO
________________________________________________________________ Maxim Integrated Products
1
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.
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