General Description
The MAX2645 is a versatile, high-linearity, low-noise
amplifier designed for 3.4GHz to 3.8GHz wireless local
loop (WLL), wireless broadband access, and digital
microwave radio applications. The device features an
externally adjustable bias control, set with a single resistor, that allows the user to meet minimum linearity requirements while minimizing current consumption. The
amplifier’s high-gain, low-noise performance and
adjustable input third-order intercept (IP3) allow it to be
used as a low-noise amplifier (LNA) in the receive path, a
PA predriver in the transmit path, or as an LO buffer.
The MAX2645 features a logic-level gain control that provides a 25dB step reduction in gain, which improves IP3
performance for operation during high input signal level
conditions. Supply current is reduced from 9mA in highgain mode to 3mA in low-gain mode. The device also
includes a logic-controlled shutdown mode, which
reduces supply current to 0.1µA. The MAX2645 operates
from a +3V to +5.5V supply and is offered in the miniature
10-pin µMAX package (5mm ✕3mm) with an exposed
paddle. Its performance has been optimized for use with
the MAX2683/MAX2684 3.5GHz SiGe mixers to provide a
complete high-performance, front-end solution for 3.5GHz
applications.
Applications
Wireless Local Loop
Wireless Broadband Access
Digital Microwave Radios
Features
♦ 3.4GHz to 3.8GHz Frequency Range
♦ LNA Performance (High/Low-Gain Modes)
Gain: +14.4dB/-9.7dB
NF: 2.3dB/15.5dB
Input IP3: +4dBm/+13dBm
Supply Current: 9.2mA/2.7mA
♦ Highly Versatile Application
Receive Path 1st and 2nd Stage LNA
Transmit PA Predriver
LO Buffer
♦ Adjustable IP3 and Supply Current
♦ 0.1µA Supply Current in Shutdown Mode
♦ +3.0V to +5.5V Single-Supply Operation
♦ 10-Pin µMAX-EP Package (5.0mm x 3.0mm)
MAX2645
________________________________________________________________ Maxim Integrated Products 1
19-1759; Rev 0; 7/00
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
Ordering Information
Pin Configuration appears at end of data sheet.
PART TEMP. RANGE
PIN-PACKAGE
MAX2645EUB -40°C to +85°C 10 µMAX-EP*
*Exposed paddle
Typical Operating Circuit
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
V
CC
GAIN STEP
LOGIC
INPUTS
INPUT
3.5GHz
SHUTDOWN
R
BIAS
RF
C1
RFIN
Z1
GND
BIAS AND POWER
HIGH
GAIN
LOW
GAIN
MANAGEMENT
MAX2645
RADIAL STUB
APPLICATION
CIRCUIT
LNA, LOW NF 14.4/-9.7 2.3/15.5
LNA, HIGH IP3
PA PREDRIVER
T
LINE
RF
OUTPUT
GAIN
(dB)
14.9/-10.7
15.2/-9.7
NF
(dB)
2.6/16
2.6/16
IIP3
(dBm)
+4/+13
+10/+15.5
+11.8/+16.2
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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 +6.0V
GAIN, SHDN, RFOUT to GND .....................0.3V to (V
CC
+ 0.3V)
RFIN Input Power (50Ω source)........................................16dBm
Minimum R
BIAS
....................................................................10kΩ
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX-EP
(derate 10.3mW/°C above T
A
= +70°C) ....................825mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
DC ELECTRICAL CHARACTERISTICS
(VCC= +3.0V to +5.5V, GAIN = SHDN = VCC, R
BIAS
= 20kΩ, no RF signals applied, TA= -40°C to +85°C. Typical values are at V
CC
= +3.3V, TA= +25°C, unless otherwise indicated.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage 3.0
V
GAIN = V
CC
9.2
R
BIAS
= 20kΩ,
T
A
= +25°C
GAIN = GND 2.7
GAIN = V
CC
R
BIAS
= 20kΩ,
T
A
= -40°C to +85°C
GAIN = GND
GAIN = V
CC
12
Operating Supply Current
R
BIAS
= 15kΩ,
T
A
= +25°C
GAIN = GND 3.6
mA
Shutdown Supply Current SHDN = GND 0.1 2 µA
Input Logic Voltage High GAIN, SHDN 2.0 V
Input Logic Voltage Low GAIN, SHDN
V
GAIN = SHDN = V
CC
1
Input Logic Bias Current
GAIN = SHDN = GND -10
µA
5.5
10.9
3.9
11.6
4.0
0.6
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
_______________________________________________________________________________________ 3
AC ELECTRICAL CHARACTERISTICS—LNA (Low-Noise Figure Application Circuit)
(MAX2645 EV kit, VCC= GAIN = SHDN = +3.3V,R
BIAS
= 20kΩ ±1%, P
RFIN
= -20dBm, f
RFIN
= 3550MHz, Zo= 50Ω,
T
A
= +25°C, unless otherwise noted.)
PARAMETER CONDITIONS
Frequency Range (Note 1)
GAIN = V
CC
Gain (Note 2)
GAIN = GND
dB
Gain Variation over Temperature TA = -40°C to +85°C, GAIN = VCC or GND (Note 3)
dB
Gain Step
dB
GAIN = VCC (Note 4) +4
Input Third-Order Intercept
GAIN = GND (Note 5)
GAIN = V
CC
-5
Input 1dB Compression Point
GAIN = GND 0
GAIN = VCC (Notes 3, 6) 2.3 3.0
Noise Figure
GAIN = GND
dB
GAIN = V
CC
25
Reverse Isolation
GAIN = GND 19
dB
Gain Step Transition Time (Note 7) 1 µs
Turn-On/Turn-Off Time (Note 8) 0.5 µs
AC ELECTRICAL SPECIFICATIONS—LNA (High-Input IP3 Application Circuit)
(MAX2645 EV kit, VCC= GAIN = SHDN = +3.3V,R
BIAS
= 20kΩ ±1%, P
RFIN
= -20dBm, f
RFIN
= 3550MHz, Zo= 50Ω,
T
A
= +25°C, unless otherwise noted.)
PARAMETER CONDITIONS
UNITS
Frequency Range (Note 1)
MHz
GAIN = V
CC
Gain
GAIN = GND
dB
Gain Variation over Temperature TA = -40°C to +85°C, GAIN = VCC or GND
dB
Gain Step
dB
GAIN = VCC (Note 5)
Input Third-Order Intercept
GAIN = GND (Note 6)
dBm
GAIN = V
CC
-4
Input 1dB Compression Point
GAIN = GND 0
dBm
GAIN = V
CC
2.6
Noise Figure
GAIN = GND 16
dB
GAIN = V
CC
25
Reverse Isolation
GAIN = GND 19
dB
MIN TYP MAX UNITS
3400 3800 MHz
12.9 14.4 15.4
-11.8 -9.7 -8.0
±0.3 ±0.7
±24.1
+13
15.5
dBm
dBm
MIN TYP MAX
3400 3800
14.9
-10.7
±0.3
25.6
+10.0
+15.5
7
8
9
10
11
12
13
14
15
3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(HIGH-GAIN MODE)
MAX2645-01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
TA = +25°C
TA = +85°C
TA = -40°C
TA = +25°C
TA = +85°C
R
BIAS
= 20kΩ
TA = -40°C
R
BIAS
= 15kΩ
2.0
3.0
2.5
4.0
3.5
4.5
5.0
3.0 4.03.5 4.5 5.0 5.5
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(LOW-GAIN MODE)
MAX2645-02
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
TA = +85°C
TA = +25°C
TA = +25°C
TA = +85°C
TA = -40°C
TA = -40°C
R
BIAS
= 15kΩ
R
BIAS
= 20kΩ
20
15
10
5
0
15 20 25
SUPPLY CURRENT vs. R
BIAS
MAX2645-03
R
BIAS
(kΩ)
SUPPLY CURRENT (mA)
HIGH GAIN
LOW GAIN
VCC = 3.3V
VCC = 5V
VCC = 5V
VCC = 3.3V
Typical Operating Characteristics
(MAX2645 EV kit, VCC= +3.3V, R
BIAS
= 20kΩ, f
RFIN
= 3550MHz, TA = +25°C, unless otherwise noted.)
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
4 _______________________________________________________________________________________
AC ELECTRICAL SPECIFICATIONS—PA Predriver Application Circuit
(MAX2645 EV kit, VCC= GAIN = SHDN = +3.3V,R
BIAS
= 20kΩ ±1%, P
RFIN
= -20dBm, f
RFIN
= 3550MHz, Zo= 50Ω,
T
A
= +25°C, unless otherwise noted.)
PARAMETER CONDITIONS
UNITS
Frequency Range (Note 1)
MHz
GAIN = V
CC
Gain
GAIN = GND
dB
Gain Variation over Temperature TA = -40°C to +85°C, GAIN = VCC or GND
dB
Gain Step
dB
GAIN = VCC (Note 5)
Input Third-Order Intercept
GAIN = GND (Note 6)
dBm
GAIN = V
CC
Input 1dB Compression Point
GAIN = GND 0
dBm
GAIN = V
CC
2.6
Noise Figure
GAIN = GND 16
dB
GAIN = V
CC
25
Reverse Isolation
GAIN = GND 19
dB
Note 1: This is the recommended operating frequency range. Operation outside this frequency range is possible but has not been
characterized. The device is characterized and tested at 3550MHz. For optimum performance at a given frequency, the output matching network must be properly designed. See Applications Information section.
Note 2: Specifications are corrected for board losses (0.25dB at input, 0.25dB at output).
Note 3: Guaranteed by design and characterization.
Note 4: Input IP3 measured with two tones, f
1
= 3550MHz and f2= 3551MHz, at -20dBm per tone.
Note 5: Input IP3 measured with two tones, f
1
= 3550MHz and f2= 3551MHz, at -12dBm per tone.
Note 6: Specifications are corrected for board losses (0.25dB at input).
Note 7: Time from when GAIN changes state to when output power reaches 1dB of its final value.
Note 8: Time from when SHDN changes state to when output power reaches 1dB of its final value.
MIN TYP MAX
3400 3800
15.2
-9.7
±0.3
24.9
+11.8
+16.2
-1.8
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(MAX2645 EV kit, VCC= +3.3V, R
BIAS
= 20kΩ, f
RFIN
= 3550MHz, TA = +25°C, unless otherwise noted.)
GAIN vs. FREQUENCY
(HIGH-GAIN MODE)
17
16
15
14
13
12
GAIN (dB)
11
10
9
8
LOW-NOISE FIGURE CIRCUIT
7
3.4 3.5 3.6 3.7 3.8
TA = +25°C
FREQUENCY (GHz)
TA = -40°C
TA = +85°C
GAIN vs. SUPPLY VOLTAGE
(LOW-GAIN MODE)
-7.0
-7.5
-8.0
-8.5
-9.0
GAIN (dB)
-9.5
-10.0
-10.5
LOW-NOISE FIGURE CIRCUIT
-11.0
3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)
TA = -40°C
TA = +25°C
TA = +85°C
MAX2645-04
MAX2645-07
GAIN vs. FREQUENCY
(LOW-GAIN MODE)
-5
-6
-7
-8
-9
-10
GAIN (dB)
-11
-12
-13
-14
-15
TA = -40°C
TA = +25°C
TA = +85°C
LOW-NOISE FIGURE CIRCUIT
3.4 3.5 3.6 3.7 3.8
FREQUENCY (GHz)
GAIN STEP
vs. SUPPLY VOLTAGE
26.0
25.5
25.0
24.5
24.0
GAIN STEP (dB)
23.5
23.0
22.5
22.0
TA = +85°C
LOW-NOISE FIGURE CIRCUIT
3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)
TA = +25°C
TA = -40°C
MAX2645-05
MAX2645-08
15.0
14.8
14.6
14.4
14.2
14.0
GAIN (dB)
13.8
13.6
13.4
13.2
13.0
15.0
14.8
14.6
GAIN (dB)
14.4
14.2
14.0
GAIN vs. SUPPLY VOLTAGE
(HIGH-GAIN MODE)
TA = -40°C
TA = +25°C
TA = +85°C
LOW-NOISE FIGURE CIRCUIT
3.0 3.5 4.5 5.0 5.5
4.0
SUPPLY VOLTAGE (V)
GAIN vs. R
BIAS
(HIGH-GAIN MODE)
VCC = 5V
VCC = 3.3V
LOW-NOISE FIGURE CIRCUIT
15.0 20.017.5 22.5 25.0
R
(kΩ)
BIAS
MAX2645-06
MAX2645-09
GAIN vs. R
BIAS
(LOW-GAIN MODE)
-10.0
-10.2
-10.4
-10.6
-10.8
-11.0
GAIN (dB)
-11.2
-11.4
-11.6
-11.8
LOW-NOISE FIGURE CIRCUIT
-12.0
15.0 17.5 20.0 22.5 25.0
R
BIAS
VCC = 5V
VCC = 3.3V
(kΩ)
MAX2645-10
NOISE FIGURE vs. FREQUENCY
(HIGH-GAIN MODE)
5
4
3
2
NOISE FIGURE (dB)
1
LOW-NOISE FIGURE CIRCUIT
0
3.4 3.63.5 3.7 3.8
FREQUENCY (GHz)
MAX2645-11
NOISE FIGURE vs. FREQUENCY
(LOW-GAIN MODE)
20
19
18
17
16
15
14
NOISE FIGURE (dB)
13
12
11
LOW-NOISE FIGURE CIRCUIT
10
3.4 3.5 3.6 3.7 3.8
FREQUENCY (GHz)
MAX2645-12
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(MAX2645 EV kit, VCC= +3.3V, R
BIAS
= 20kΩ, f
RFIN
= 3550MHz, TA = +25°C, unless otherwise noted.)
0
1
3
2
4
5
NOISE FIGURE vs. R
BIAS
(HIGH-GAIN MODE)
MAX2645-13
R
BIAS
(kΩ)
NOISE FIGURE (dB)
15.0 20.017.5 22.5 25.0
LOW-NOISE FIGURE CIRCUIT
1.0
2.5
2.0
1.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
3.0 3.5 4.5 5.0 5.5
INPUT IP3 vs. SUPPLY VOLTAGE
(HIGH-GAIN MODE)
MAX2645-14
SUPPLY VOLTAGE (V)
INPUT IP3 (dBm)
4.0
TA = -40°C
TA = +85°C
TA = +25°C
LOW-NOISE FIGURE CIRCUIT
10.5
12.0
11.5
11.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
3.0 3.5 4.5 5.0 5.5
INPUT IP3 vs. SUPPLY VOLTAGE
(LOW-GAIN MODE)
MAX2645-15
SUPPLY VOLTAGE (V)
INPUT IP3 (dBm)
4.0
TA = +85°C
TA = +25°C
TA = -40°C
LOW-NOISE FIGURE CIRCUIT
-1
1
5
3
7
9
INPUT IP3 vs. R
BIAS
(HIGH-GAIN MODE)
MAX2645-16
R
BIAS
(kΩ)
INPUT IP3 (dBm)
15.0 20.017.5 22.5 25.0
VCC = 5V
VCC = 3.3V
LOW-NOISE FIGURE CIRCUIT
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
15.0 17.5 20.0 22.5 25.0
INPUT IP3 vs. R
BIAS
(LOW-GAIN MODE)
MAX2645-17
R
BIAS
(kΩ)
INPUT IP3 (dBm)
VCC = 5V
VCC = 3.3V
LOW-NOISE FIGURE CIRCUIT
-8.5
-7.0
-7.5
-8.0
-6.5
-6.0
-5.5
-5.0
-4.5
-4.0
-3.5
3.0 3.5 4.5 5.0 5.5
INPUT P1dB vs. SUPPLY VOLTAGE
(HIGH-GAIN MODE)
MAX2645-18
SUPPLY VOLTAGE (V)
INPUT P1dB (dBm)
4.0
TA = -40°C
TA = +25°C
TA = +85°C
LOW-NOISE FIGURE CIRCUIT
-25
-15
-20
-5
-10
5
0
10
-10.0 -5.0 0 5.0
OUTPUT POWER vs. INPUT POWER
(LOW-GAIN MODE)
MAX2645-19
INPUT POWER (dBm)
OUTPUT POWER (dBm)
TA = +25°C
TA = +85°C
TA = -40°C
LOW-NOISE FIGURE CIRCUIT
-6
-7
-4
-5
-3
-2
INPUT P1dB vs. R
BIAS
(HIGH-GAIN MODE)
MAX2645-20
R
BIAS
(kΩ)
INPUT P1dB (dBm)
15.0 20.017.5 22.5 25.0
VCC = 5V
VCC = 3.3V
LOW-NOISE FIGURE CIRCUIT
1.00
1.50
1.25
2.00
1.75
2.25
2.50
3.4 3.63.5 3.7 3.8
INPUT VSWR vs. FREQUENCY
MAX2645-21
FREQUENCY (GHz)
VSWR
HIGH GAIN
LOW GAIN
LOW-NOISE FIGURE CIRCUIT
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(MAX2645 EV kit, VCC= +3.3V, R
BIAS
= 20kΩ, f
RFIN
= 3550MHz, TA = +25°C, unless otherwise noted.)
OUTPUT VSWR vs. FREQUENCY
6.0
LOW-NOISE FIGURE CIRCUIT
5.5
5.0
VSWR
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
LOW GAIN
HIGH GAIN
3.4 3.5 3.6 3.7 3.8
FREQUENCY (GHz)
GAIN vs. FREQUENCY
(LOW-GAIN MODE)
-10.0
-10.5
-11.0
-11.5
-12.0
-12.5
GAIN (dB)
-13.0
-13.5
-14.0
-14.5
-15.0
TA = +25°C
TA = -40°C
HIGH-INPUT IP3 CIRCUIT
3.4 3.5 3.6 3.7 3.8
FREQUENCY (GHz)
TA = +85°C
MAX2645-22
MAX2645-25
GAIN vs. FREQUENCY
REVERSE ISOLATION vs. FREQUENCY
0
LOW-NOISE FIGURE CIRCUIT
-5
-10
-15
LOW GAIN
-20
-25
REVERSE ISOLATION (dB)
HIGH GAIN
-30
-35
3.4 3.5 3.6 3.7 3.8
FREQUENCY (GHz)
INPUT VSWR
vs. FREQUENCY
5.0
HIGH-INPUT IP3 CIRCUIT
4.5
4.0
3.5
3.0
VSWR
2.5
2.0
1.5
1.0
LOW GAIN
HIGH GAIN
3.4 3.5 3.6 3.7 3.8
FREQUENCY (GHz)
MAX2645-23
MAX2645-26
17.0
16.5
16.0
15.5
15.0
14.5
GAIN (dB)
14.0
13.5
13.0
12.5
12.0
3.4 3.5 3.6 3.7 3.8
20
VCC = 5V
19
18
17
16
15
GAIN (dB)
14
13
12
11
10
3.4 3.5 3.6 3.7 3.8
(HIGH-GAIN MODE)
HIGH-INPUT IP3 CIRCUIT
TA = -40°C
TA = +25°C
TA = +85°C
FREQUENCY (GHz)
GAIN vs. FREQUENCY
(HIGH-GAIN MODE)
TA = -40°C
TA = +25°C
TA = +85°C
PA PREDRIVER CIRCUIT
FREQUENCY (GHz)
MAX2645-24
MAX2645-27
GAIN vs. FREQUENCY
(LOW-GAIN MODE)
-5
VCC = 5V
-6
-7
-8
-9
-10
TA = -40°C
GAIN (dB)
-11
-12
-13
-14
PA PREDRIVER CIRCUIT
-15
3.4 3.5 3.6 3.7 3.8
TA = +85°C
TA = +25°C
FREQUENCY (GHz)
MAX2645-28
GAIN vs. SUPPLY VOLTAGE
(HIGH-GAIN MODE)
16.5
VCC = 5V
16.0
15.5
15.0
14.5
GAIN (dB)
14.0
13.5
13.0
PA PREDRIVER CIRCUIT
12.5
3.0 3.5 4.0 4.5 5.0 5.5
TA = -40°C
TA = +25°C
TA = +85°C
SUPPLY VOLTAGE (V)
MAX2645-29
GAIN vs. SUPPLY VOLTAGE
(LOW-GAIN MODE)
-8.5
VCC = 5V
-9.0
TA = -40°C
-9.5
-10.0
-10.5
GAIN (dB)
-11.0
-11.5
-12.0
PA PREDRIVER CIRCUIT
-12.5
3.0 3.5 4.0 4.5 5.0 5.5
TA = +25°C
TA = +85°C
SUPPLY VOLTAGE (V)
MAX2645-30
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(MAX2645 EV kit, VCC= +3.3V, R
BIAS
= 20kΩ, f
RFIN
= 3550MHz, TA = +25°C, unless otherwise noted.)
7
9
8
3.0 4.03.5 4.5 5.0 5.5
OUTPUT P1dB POINT vs. SUPPLY VOLTAGE
(HIGH-GAIN MODE)
MAX2645-31
SUPPLY VOLTAGE (V)
TA = +25°C
TA = +85°C
TA = -40°C
PA PREDRIVER CIRCUIT
VCC = 5V
-25
-15
-20
-5
-10
5
0
10
-10.0 -5.0 0 5.0
OUTPUT POWER vs. INPUT POWER
(LOW-GAIN MODE)
MAX2645-32
INPUT POWER (dBm)
OUTPUT POWER (dBm)
TA = +25°C
TA = +85°C
TA = -40°C
PA PREDRIVER CIRCUIT
VCC = 5V
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
3.4 3.5 3.6 3.7 3.8
INPUT VSWR vs. FREQUENCY
MAX2645-33
FREQUENCY (GHz)
VSWR
HIGH GAIN
LOW GAIN
PA PREDRIVER CIRCUIT
VCC = 5V
Pin Description
PIN NAME FUNCTION
1, 2, 4, 7,
EP
GND
Ground. Connect to ground plane with a low-inductance connection. Solder exposed paddle evenly
to the board ground plane.
3 RFIN
RF Input Port to Amplifier. Requires a matching network and a DC-blocking capacitor that may be
part of this network. See Figure 1 for recommended component values.
5 BIAS
Bias-Setting Resistor Connection. A resistor, R
BIAS
, placed from BIAS to ground sets the linearity
and supply current of the amplifier.
6 RFOUT
RF Open-Collector Output Port of Amplifier. Requires a matching network composed of an
inductance to VCC and a DC-blocking capacitor. See Figure 1 for recommended component
values.
8 SHDN
Shutdown Control Logic-Level Input. A logic high enables the device for normal operation. A logic
low places the device in low-power shutdown mode.
9 GAIN
Gain Control Logic-Level Input. A logic high places the device in high-gain mode. A logic low
places the device in low-gain mode, reducing the gain by 25dB.
10 V
CC
Power Supply Input. Bypass directly to ground with a capacitor as close to the supply pin as
possible. See Figure 1 for recommended component values.
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
_______________________________________________________________________________________ 9
Detailed Description
The MAX2645 is a versatile amplifier with high-gain,
high-linearity, and low-noise performance—features that
make it suitable for use as an LNA, high-linearity/lownoise amplifier, PA predriver, or LO buffer in the 3.4GHz
to 3.8GHz frequency range. See Figure 1, MAX2645
Typical Application Circuit, for recommended component values. A single external bias-setting resistor allows
the system designer to trade off linearity for reduced
supply current. A logic-level control reduces gain by a
25dB step to further improve input IP3 performance. A
low-power shutdown mode disables the device and
reduces current consumption to 0.1µA.
Bias Circuitry
The linearity and supply current of the MAX2645 are
externally programmable with a single resistor (R
BIAS
)
placed from BIAS to GND. Larger resistor values result
in lower IP3 performance and lower supply current, while
smaller resistor values result in higher IP3 performance
and higher supply current. Use resistor values in the
15kΩ to 25kΩ range, with a nominal value of 20kΩ
suitable for most applications. See Typical Operating
Characteristics for performance variation vs. R
BIAS
value.
Gain Step Control
The MAX2645 features a logic-level gain step control
input (GAIN) that places the device in high-gain or lowgain mode. A logic-level high places the device in highgain mode, where the gain is 14.5dB. A logic-level low
places the device in low-gain/high-linearity mode, where
the gain is reduced to 10dB and the input IP3 performance is increased.
Shutdown Control
The MAX2645 features a logic-level shutdown control
input. A logic high on SHDN enables the device for normal operation. A logic low on SHDN disables all device
functions and reduces supply current to 0.1µA.
Applications Information
RF Input
The RFIN port is internally biased and requires an external DC-blocking capacitor. A matching network is
required for best performance. Figure 1 shows component values optimized for best noise-figure performance,
low-noise figure, high-input IP3 performance, and highoutput P1dB performance in the 3.4GHz to 3.8GHz frequency range. For matching to other frequencies, see
Tables 1 and 2.
Table 1. MAX2645 S-Parameters
S11 S21 S12 S22
FREQ
(MHz)
MAG PHASE MAG PHASE MAG PHASE MAG PHASE
R
BIAS
= 20kΩ, VCC = +3.3V, TA = +25°C
3400 0.468 -149.8 5.061 -44.6 0.053 -55.5 0.660 -57.0
3450 0.466 -150.4 4.975 -46.3 0.058 -60.8 0.658 -58.4
3500 0.472 -151.6 5.098 -49.9 0.056 -64.6 0.661 -60.6
3550 0.469 -153.4 4.883 -53.7 0.054 -62.7 0.658 -63.0
3600 0.471 -154.6 4.814 -53.7 0.056 -64.4 0.647 -64.2
3650 0.477 -155.0 5.118 -57.4 0.058 -68.9 0.657 -66.2
3700 0.485 -156.6 4.769 -63.4 0.054 -70.5 0.657 -69.8
3750 0.484 -156.5 4.780 -62.3 0.058 -72.0 0.654 -70.9
3800 0.492 -157.0 4.939 -66.6 0.060 -75.4 0.654 -72.3
R
BIAS
= 15kΩ, VCC = +5V, TA = +25°C
3400 0.454 -146.6 5.350 -41.8 0.057 -51.3 0.651 -52.3
3450 0.457 -147.4 5.245 -43.5 0.061 -56.7 0.646 -53.7
3500 0.465 -147.9 5.375 -46.6 0.060 -61.2 0.654 -55.6
3550 0.468 -149.7 5.165 -50.3 0.057 -61.0 0.652 -58.3
3600 0.472 -150.5 5.066 -50.2 0.060 -62.7 0.645 -59.3
3650 0.481 -150.5 5.386 -53.4 0.063 -67.6 0.652 -60.7
3700 0.486 -152.2 5.040 -59.4 0.060 -67.8 0.648 -63.9
3750 0.486 -152.4 5.019 -58.3 0.062 -67.0 0.642 -64.8
3800 0.499 -152.6 5.207 -62.0 0.065 -73.3 0.643 -66.2
RF Output
The RFOUT port is an open-collector output that must be
tied to VCCthrough an inductance for proper biasing.
The MAX2645 EV kit uses a length of transmission line
equivalent to 1.5nH of inductance. A DC-blocking
capacitor is required and can be part of the output
matching network. See Figure 1 for component values
recommended for operation over the 3.4GHz to 3.8GHz
frequency range. See Table 1 for matching to other frequencies. This transmission line is terminated at the
VCCnode with a radial stub for high-frequency bypassing. This arrangement provides a high-Q, low-loss bias
network used to optimize performance. The radial stub
can be replaced with an appropriate microwave
capacitor.
Power-Supply, Bias Circuitry, and Logic-
Input Bypassing
Proper power-supply bypassing is essential for high-frequency circuit stability. Bypass VCCwith 10µF, 0.1µF,
and 50pF capacitors located as close to the VCCpin as
possible.
To minimize the amount of noise injected into the bias
circuitry and logic inputs, bypass the pins with capacitors located as near to the device pin as possible. For
additional isolation on the logic-control pins, place resistors between the logic-control inputs and the bypass
capacitors. See Figure 1 for recommended component
values; refer to MAX2645 EV kit manual for recommended board layout.
Layout Considerations
A properly designed PC board is an essential part of any
RF/microwave circuit. Keep RF signal lines as short as
possible to reduce losses, radiation, and inductance.
Use separate, low-inductance vias to the ground plane
for each ground pin. For best performance, solder the
exposed paddle on the bottom of the device package
evenly to the board ground plane.
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
10 ______________________________________________________________________________________
Table 2. MAX2645 Noise Parameters
FREQUENCY (MHz) F
3400 2.098 0.237 144.1
3450 2.122 0.235 146.1
3500 2.148 0.235 148.2
3550 2.173 0.234 150.3
3600 2.198 0.233 152.4
3650 2.225 0.232 154.5
3700 2.251 0.231 156.5
3750 2.279 0.230 158.6
3800 2.306 0.229 160.7
3400 2.103 0.210 146.3
3450 2.127 0.209 148.4
3500 2.152 0.208 150.5
3550 2.177 0.207 152.6
3600 2.203 0.206 154.7
3650 2.229 0.206 156.8
3700 2.256 0.205 158.9
3750 2.282 0.204 161.0
3800 2.310 0.204 163.1
(dB) |Γ
MIN
| Γ
opt
R
= 20kΩ, VCC = +3.3V, TA = +25°C
BIAS
R
= 15kΩ, VCC = +5V, TA = +25°C
BIAS
opt
ANGLE
RN (Ω)
31.1
31.5
32.0
32.5
32.9
33.5
33.9
34.5
35.0
31.1
31.6
32.1
32.5
33.0
33.5
34.0
34.6
35.1
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
______________________________________________________________________________________ 11
Figure 1. Typical Application Circuit
Figure 2. Typical System Application Block Diagram
MAX2645
MAX2645
MAX2683
MAX2684
MAX2645
MAX2645
MAX2683
MAX2684
MAX2645
LO BUFFER
LO BUFFER
TRANSMIT
IF INPUT
RECEIVE
IF OUTPUT
LO
LO
IF
BANDPASS
FILTER
RF
IMAGE-REJECT
FILTER
HIGH IP3
LNA
LOW NF
LNA
DUPLEXER
PA
PA PREDRIVER
RF
BANDPASS
FILTER
1
GND
2
GND
MAX2645
C1
RF INPUT
3.4GHz to 3.8GHz
Z1
220pF
APPLICATION CIRCUIT
LNA, LOW NF
LNA, HIGH INPUT IP3
PA PREDRIVER
BOARD MATERIAL = GETek, COPPER THICKNESS = 1 oz
*
BOARD THICKNESS = 0.012in, DIELECTRIC CONSTANT = 3.8
3
RFIN
4
GND
5
BIAS
RF
R
BIAS
V
CC
9
GAIN
8
SHDN
7
GND
8
OUT
C1
1.5pFZ11.8nH
1000pF
0.01µF
L
EQUIV
0.75pF
0.75pF
0.75pF
47pF
T
LINE
HIGH GAIN
LOW GAIN
ON
OFF
RADIAL STUB*
= 1.5nH
RF
OUTPUT
R
BIAS
20
20
15
40°
(kΩ)
294mils
V
CC
0.1µF
V
CC
1000pF
V
(V)
CC
3.3
3.3
5.0
MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
12 ______________________________________________________________________________________
Pin Configuration
Chip Information
TRANSISTOR COUNT: 271
S
Package Information
TOP VIEW
GND
GND
RFIN
1
2
3
4
5
10
V
CC
9
MAX2645
MAX-EP
µ
GAIN
8
SHDN
7
GNDGND
RFOUTBIAS
6
10LUMAX.EP
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