General Description
The MAX2440/MAX2441/MAX2442 highly integrated
front-end receiver ICs provide the lowest cost solution for
cordless phones and ISM-band radios operating in the
900MHz band. All devices incorporate receive imagereject mixers to reduce filter cost. They operate with a
+2.7V to +4.8V power supply, allowing direct connection
to a 3-cell battery stack.
The signal 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 (IP3) of up to +2dBm.
All devices include 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. Three separate powerdown inputs can be used for system power management, including a 0.5µA shutdown mode. These parts
are compatible with commonly used modulation
schemes such as FSK, BPSK, and QPSK, as well as frequency hopping and direct sequence spread-spectrum
systems. All devices come in a 28-pin SSOP package.
Evaluation kits are available for the MAX2420/
MAX2421/MAX2422. The MAX2420/MAX2421/MAX2422
are transceivers whose receive sections and pinout are
identical to the MAX2440/MAX2441/MAX2442.
For complete transceiver devices, refer to the MAX2420/
MAX2421/MAX2422/MAX2460/MAX2463 and MAX2424/
MAX2426 data sheets.
________________________Applications
Cordless Phones Spread-Spectrum Communications
Wireless Telemetry Two-Way Paging
Wireless Networks
Features
♦ Receive Mixer with 35dB Image Rejection
♦ Adjustable-Gain LNA
♦ Up to +2dBm Combined Receiver Input IP3
♦ 4dB Combined Receiver Noise Figure
♦ Low Current Consumption:
23mA Receive
9.5mA Oscillator
♦ 0.5µA Shutdown Mode
♦ Operates from Single +2.7V to +4.8V Supply
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
________________________________________________________________ Maxim Integrated Products 1
___________________Pin Configuration
19-1352; Rev 2; 12/00
PART
MAX2440EAI
MAX2441EAI
MAX2442EAI
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
TEMP. RANGE PIN-PACKAGE
28 SSOP
28 SSOP
28 SSOP
_______________Ordering Information
Functional Diagram appears at end of data sheet.
High side
INJECTION
TYPE
fRF+ 10.7
LO FREQ
(MHz)
High side
High side
fRF+ 70
fRF+ 46
MAX2442
MAX2441
70
46
MAX2440
PART
10.7
IF FREQ
(MHz)
______________________Selector Guide
EVALU
A
TIO
N
K
IT
A
V
AILA
BLE
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.
TOP VIEW
V
CAP1
RXOUT
GND
RXIN
V
GND
GND
GND
LNAGAIN
V
GND
GND
GND
1
CC
2
3
4
5
MAX2440
6
CC
CC
MAX2441
MAX2442
7
8
9
10
11
12
13
14
SSOP
28
27
26
25
24
23
22
21
20
19
18
17
16
15
GND
GND
GND
TANK
TANK
V
CC
V
CC
PREOUT
PREGND
MOD
DIV1
VCOON
RXON
GND
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(VCC= +2.7V to +4.8V, no RF signals applied, LNAGAIN = unconnected, V
VCOON
= 2.4V, V
RXON
= V
MOD
= V
DIV1
= 0.45V, PREGND
= GND, T
A
= T
MIN
to T
MAX
. Typical values are at TA= +25°C, VCC= +3.3V, unless otherwise noted.) (Note 1)
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: ≥25°C guaranteed by production test, <25°C guaranteed through correlation to worst-case temperature testing.
Note 2: Calculated by measuring the combined oscillator and prescaler supply current and subtracting the oscillator supply current.
Note 3: Calculated by measuring the combined oscillator and LO buffer supply current and subtracting the oscillator supply current.
Note 4: 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.
V
CC
to GND...........................................................-0.3V to +5.5V
Voltage on LNAGAIN, RXON, VCOON,
DIV1, MOD .............................................-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
MAX244_EAI...................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +165°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
MIN TYP MAX UNITS
Receive Supply Current 23 36 mA
Prescaler Supply Current
(buffer mode)
5.4 8.5 mA
Oscillator Supply Current
Supply-Voltage Range 2.7 4.8 V
9.5 14 mA
Prescaler Supply Current
(divide-by-64/65 mode)
4.2 6 mA
CONDITIONS
V
RXON
= 2.4V, PREGND = unconnected (Note 4)
V
DIV1
= 2.4V (Note 3)
PREGND = unconnected
(Note 2)
Digital Input Voltage Low 0.45 V
0.5
RXON, DIV1, VCOON, MOD
VCOON = RXON = MOD =
DIV1 = GND
Digital Input Current ±1 ±10 µAVoltage on any one digital input = VCCor GND
Digital Input Voltage High V2.4RXON, DIV1, VCOON, MOD
Shutdown Supply Current
10
µA
TA= +25°C
TA= T
MIN
to T
MAX
AC ELECTRICAL CHARACTERISTICS
(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f
RXIN
= 915MHz; P
RXIN
= -35dBm; V
LNAGAIN
= 2V; V
VCOON
= V
RXON
= 2.4V; RXON = MOD = DIV1 = PREGND = GND; TA= +25°C,
unless otherwise noted.)
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
_______________________________________________________________________________________ 3
CONDITIONS UNITSMIN TYP MAXPARAMETER
MHz800 1000
36 46 55
8.5 10.7 12.5
MHz
20 22 24.5
dB
26 35Image Frequency Rejection
55 70 85
19.5 25
12
19 21 23.5
(Note 7)
-16
(Notes 5, 8) dBm
-8
Input Third-Order Intercept
-19 -17
(Note 9) ns500Receiver Turn-On Time
Receiver on or off dBm-60LO to RXIN Leakage
V
LNAGAIN
= 1V
dBm
-18
Input 1dB Compression
LNAGAIN = V
CC
-26
18 24
LNAGAIN = VCC,
T
A
= T
MIN
to T
MAX
(Note 5)
45
dB
12
Noise Figure
dB
IF Frequency Range
(Notes 5, 6)
(Notes 5, 6)
Input Frequency Range
Conversion Power Gain
DIV1 = V
CC
(Notes 5, 7)
MAX2441
MAX2442
LNAGAIN = V
CC
V
LNAGAIN
= 1V
V
LNAGAIN
= 1V
LNAGAIN = V
CC
MAX2442
V
LNAGAIN
= 1V
LNAGAIN = GND
MAX2440
LNAGAIN = VCC,
T
A
= +25°C
MAX2440/MAX2441
MAX2440/MAX2441
MAX2442
RECEIVER
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
4 _______________________________________________________________________________________
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f
RXIN
= 915MHz; P
RXIN
= -35dBm; V
LNAGAIN
= 2V; V
VCOON
= V
RXON
= 2.4V; RXON = MOD = DIV1 = PREGND = GND; TA= +25°C,
unless otherwise noted.)
Oscillator Phase Noise
Oscillator Frequency Range 690 1100 MHz
82 dBc/Hz
8
(Notes 5, 10)
10kHz offset (Note 11)
Standby to RX
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 plots showing receiver gain versus LNAGAIN voltage, input IP3 versus
LNAGAIN voltage, and noise figure versus LNAGAIN voltage.
Note 8: Two tones at P
RXIN
= -45dBm each, f1 = 915.0MHz and f2 = 915.2MHz.
Note 9: Time delay from RXON = 0.45V to RXON = 2.4V transition to the time the output envelope reaches 90% of its final value.
Note 10: Refers to useable operating range. Tuning range of any given tank circuit design is typically much narrower (refer to Figure 1).
Note 11: Using tank components L3 = 5.0nH (Coilcraft A02T), C2 = C3 = C26 = 3.3pF, R6 = R7 = 10Ω.
Note 12: This approximates a typical application in which a transmitter is followed by an external PA and a T/R switch with finite
isolation.
Note 13: Relative to the rising edge of PREOUT.
Prescaler Output Level
500 mVp-p
-11 -8
Required Modulus Setup Time 10 ns
ZL= 100kΩ
| |
10pF
Divide-by-64/65 mode (Notes 5, 13)
Standby mode with P
RXIN
= -45dBm to
P
RXIN
= 0dBm (Note 12)
70
Oscillator Buffer Output Level
-12
dBm
Oscillator Pulling kHz
PARAMETER MIN TYP MAX UNITSCONDITIONS
TA= T
MIN
to T
MAX
TA= +25°C
DIV1 = 2.4V, ZL= 50Ω
(Note 5)
OSCILLATOR AND PRESCALER
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
_______________________________________________________________________________________ 5
)
Typical Operating Characteristics
(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f
RXIN
= 915MHz; P
RXIN
= -35dBm; V
LNAGAIN
= 2V; V
VCOON
= 2.4V; RXON = VCC; MOD = DIV1 = PREGND = GND; TA= +25°C,
unless otherwise noted.)
)
42
40
38
36
34
(mA)
CC
I
32
30
28
26
24
RECEIVER SUPPLY CURRENT
VCC = 3.3V
-40 0 20-20 40 60 80 100
RECEIVER INPUT IP3 vs. V
5
LNA
OFF
0
-5
IIP3 (dBm)
-10
-15
-20
0 0.5 1.0 1.5 2.0
RECEIVER NOISE FIGURE vs.
TEMPERATURE AND SUPPLY VOLTAGE
5.5
LNAGAIN = V
DIV1 = V
5.0
4.5
4.0
NOISE FIGURE (dB)
3.5
3.0
-40 0 20-20 40 60 80 100
vs. TEMPERATURE
VCC = 4.8V
VCC = 2.7V
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
TEMPERATURE (°C)
LNA
ADJUSTABLE
PARTIALLY
BIASED
AVOID
THIS
REGION
LNAGAIN VOLTAGE (V)
CC
CC
VCC = 4.8V
TEMPERATURE (°C)
GAIN
VCC = 2.7V
LNAGAIN
VCC = 3.3V
MAX
GAIN
MAX2440/1/2-01
(µA)
CC
I
MAX2440/1/2-04
NOISE FIGURE (dB)
MAX2440/1/2-07
IIP3 (dBm)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
4.5
VCOON = GND
4.0
RXON = GND
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-40 0 20-20 406080100
VCC = 4.8V
TEMPERATURE (°C)
VCC = 3.3V
VCC = 2.7V
RECEIVER NOISE FIGURE
vs. LNAGAIN
40
LNA
35
LNA
OFF
30
25
20
15
10
5
0
0 0.5 1.0 1.5 2.0
ADJUSTABLE
PARTIALLY
BIASED
AVOID
THIS
REGION
LNAGAIN VOLTAGE (V)
GAIN
DIV1 = V
MAX
GAIN
RECEIVER INPUT IP3
vs. TEMPERATURE
-6
-8
V
= 1V
LNAGAIN
-10
-12
-14
-16
-18
-20
V
= 2V
LNAGAIN
-40 0 20-20 40 60 80 100
TEMPERATURE (°C
RECEIVER GAIN vs. LNAGAIN
25
20
MAX2440/1/2-02
15
10
5
0
-5
RECEIVER GAIN (dB)
-10
-15
-20
LNA
OFF
0 0.5 1.0 1.5 2.0
LNA
PARTIALLY
BIASED
ADJUSTABLE
GAIN
AVOID
THIS
REGION
LNAGAIN VOLTAGE (V)
MAX
GAIN
MAX2440
RECEIVER GAIN vs. TEMPERATURE
LNAGAIN = V
26
MAX2440/1/2-05
24
22
RECEIVER GAIN (dB)
20
CC
18
-40 0 20-20 406080100
CC
VCC = 4.8V
VCC = 3.3V
TEMPERATURE (°C)
VCC = 2.7V
MAX2440
RXOUT 1dB COMPRESSION POINT
vs. TEMPERATURE
-3
-4
MAX2440/1/2-08
1dB COMPRESSION POINT (dBm)
VCC = 4.8V
-5
-6
-7
-8
-9
-40 0 20-20 40 60 80
VCC = 3.3V
TEMPERATURE (°C
VCC = 2.7V
MAX2440/1/2-03
MAX2440/1/2-06
MAX2440/1/2-9
550
500
0
11k10k100 100k
PRESCALER OUTPUT LEVEL
vs. LOAD RESISTANCE
100
50
MAX2440/1/2-13
LOAD RESISTANCE (Ω)
PRESCALER OUTPUT LEVEL (mVp-p)
200
150
350
300
250
450
400
LOAD IS PLOTTED RESISTANCE
IN PARALLEL WITH A 10pF
OSCILLOSCOPE PROBE
(÷ 64/65 MODE)
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(MAX242X/MAX246X EV kit, VCC= +3.3V; fLO= 925.7MHz (MAX2440), fLO= 961MHz (MAX2441), fLO= 985MHz (MAX2442),
f
RXIN
= 915MHz; P
RXIN
= -35dBm; V
LNAGAIN
= 2V; V
VCOON
= 2.4V; RXON = VCC; 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
MAX2440/1/2-10
RF FREQUENCY (MHz)
IMAGE REJECTION (dB)
RXON = V
CC
40
0
1 100010010
RECEIVER IMAGE REJECTION
vs. IF FREQUENCY
20
15
10
5
30
25
35
MAX2440/1/2-11
IF FREQUENCY (MHz)
IMAGE REJECTION (dB)
MAX2440
MAX2441
MAX2442
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
MAX2440/1/2-12
FREQUENCY (MHz)
REAL IMPEDANCE (Ω)
REAL
IMAGINARY
IMAGINARY IMPEDANCE (Ω)
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
_______________________________________________________________________________________ 7
Pin Description
DIV118
Driving DIV1 with a logic high disables the divide-by-64/65 prescaler and connects the PREOUT pin
directly to an oscillator buffer amplifier, which outputs -8dBm into a 50Ω load. Tie DIV1 low for divide-by64/65 operation. Pull this pin low when in shutdown to minimize off current.
RXON
VCOON
MOD
16
Driving RXON with a logic high enables the LNA, receive mixer, and IF output buffer. VCOON must also
be high.
17
Driving VCOON with a logic high turns on the VCO, phase shifters, VCO buffers, and prescaler. The
prescaler can be selectively disabled by floating the PREGND pin.
19
Modulus Control for the Divide-by-64/65 Prescaler: high = divide-by-64, low = divide-by-65. Note that
the DIV1 pin must be at logic low when using the prescaler mode.
PREGND
PREOUT
20
V
CC
11
Supply Voltage Input for Signal-Path Blocks, except LNA. Bypass with a 47pF low-inductance capacitor
and 0.01µF to GND (pin 8 recommended).
GND8 Ground Connection for Signal-Path Blocks, except LNA. Connect directly to ground plane.
NAME
V
CC
CAP1
RXOUT
GND7 Ground Connection for Receive Low-Noise Amplifier. Connect directly to ground plane using multiple vias.
LNAGAIN10
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.
PIN FUNCTION
1
Supply-Voltage Input for Master Bias Cell. Bypass with a 47pF low-inductance capacitor and 0.1µF to
GND (pin 28 recommended).
2
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.
3 Single-Ended, 330Ω IF Output. AC couple to this pin.
Ground connection for the Prescaler. Tie PREGND to ground for normal operation. Leave floating to
disable the prescaler and the output buffer. Tie MOD and DIV1 to ground and leave PREOUT floating
when disabling the prescaler.
21
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.
GND
RXIN
V
CC
4, 9,
12–15
Ground Connection
5
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.
6
Supply Voltage Input for Receive Low-Noise Amplifier. Bypass with a 47pF low-inductance capacitor to
GND (pin 7 recommended).
V
CC
22
Supply-Voltage Input for Prescaler. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND
(pin 20 recommended).
V
CC
23
Supply-Voltage Input for VCO and Phase Shifters. Bypass with a 47pF low-inductance capacitor to GND
(pin 26 recommended).
TANK
24
Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using
an external oscillator.
TANK25
Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using
an external oscillator.
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
8 _______________________________________________________________________________________
Pin Description (continued)
Ground Connection for VCO and Phase Shifters26 GND
Ground (substrate)27 GND
Ground Connection for Master Bias Cell28 GND
FUNCTIONPIN NAME
Figure 1. Typical Operating Circuit
V
CC
RECEIVE
RF INPUT
0.1µF
8.2nH
12nH
47pF
47pF0.1µF
47pF
47pF
V
CC
0.01µF
LNAGAIN
47pF
47pF
1
V
CCVCC
28
GND
2
CAP1
5
RXIN
MAX2440
MAX2441
V
PREGND
V
GND
GND
RXOUT
CC
CC
MAX2442
GND
9
GND
6
V
V
CC
CC
7
GND
11
V
CC
8
GND
13
GND
14
GND
4
GND
10
LNAGAIN
TANK
TANK
PREOUT
MOD
DIV1
VCOON
RXON
GND
V
CC
22
47pF
20
V
CC
23
47pF
26
27
3
12
25
24
21
19
18
17
16
15
0.01µF
VARACTOR:
ALPHA SMV1299-004
OR EQUIVALENT
R7
R6
1000pF
0.01µF
VCO TANK COMPONENTS FOR
915MHz TYPICAL RF
C26
V
CC
100nH
C2
C3
L3
(nH)
6.8
3.3
3.3
(pF)
1.8
3.6
3.0
PART
MAX2440
MAX2441
MAX2442
SEE APPLICATIONS INFORMATION SECTION
L3: COILCRAFT 0805HS-060TMBC
RECEIVE IF OUTPUT (330Ω)
L3 C26
TO PLL
MOD
DIV1
VCOON
RXON
1k
47k
1k
C2, C3
(pF)
3.3
4.0
4.0
R6, R7
(Ω)
10
15
15
VCO
ADJUST
47pF
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
_______________________________________________________________________________________ 9
Detailed Description
The following sections describe each of the blocks
shown in the Functional Diagram.
Receiver
The MAX2440/MAX2441/MAX2442’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 can provide
optimum performance over a wide range of signal levels. The LNA can be placed in four modes by applying
a DC voltage 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 the mixer
to provide maximum linearity for large-signal operation
(receiver close to transmitter). As the LNAGAIN voltage
is raised, the LNA begins to turn 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 at LNAGAIN voltages above 1V. See the
Receiver Gain, Receiver IP3, and Receiver 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.
The local-oscillator (LO) port of each mixer is driven
from a quadrature LO. The LO is generated from an onchip oscillator and an external tank circuit. Its signal is
buffered and split into phase shifters, which provide
90° of phase shift across their outputs. This pair of LO
signals is fed to the mixers. The mixers’ outputs are
then passed 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.
Phase Shifters
MAX2440/MAX2441/MAX2442 devices use passive
networks to provide quadrature phase shifting for the
receive IF and LO signals. Because these networks are
frequency selective, proper part selection is important.
Image rejection degrades as the IF and RF move away
from the designed optimum frequencies. Refer to the
Selector Guide on the front page of this data sheet.
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 and Figure 2 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 and Figure 3 for
details.
The local oscillator resists LO pulling caused by changes
in load impedance that occur as the part is switched
from standby mode. The amount of LO pulling will be
affected if there is power at the RXIN port due to imperfect isolation in an external transmit/receive (T/R) switch.
Prescaler
The on-chip prescaler can be used in two different
modes: as a dual-modulus divide-by-64/65, or as 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 mode, the division ratio is controlled
by the MOD pin. When MOD is high, the prescaler is in
divide-by-64 mode; when it is low, it divides the LO frequency by 65. The DIV1 pin must be at a logic low in
this mode.
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 ≤ V
CC
1.0 < V ≤ 1.5
0.5 < V < 1.0
0 < V ≤ 0.5
LNAGAIN
VOLTAGE (V)
Table 1. LNA Modes
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
10 ______________________________________________________________________________________
To disable the prescaler entirely, leave PREGND and
PREOUT floating. Also tie the MOD and DIV1 pins to
GND. Disabling the prescaler does not affect operation
of the VCO stage.
Power Management
MAX2440/MAX2441/MAX2442 supports three different
power-management 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. The VCO can be
powered up prior to receiving to allow it to stabilize. 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.
To disable all chip functions and reduce the supply
current to typically less than 0.5µA, pull VCOON, DIV1,
MOD, and RXON low.
Applications Information
Oscillator Tank
The on-chip oscillator requires a parallel-resonant tank
circuit connected across TANK and TANK. Figure 2
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 (LT). 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 will 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.
For applications that require a wide tuning range and
low phase noise, a series coupled resonant tank may
be required, as shown in Figure 4. 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 0Ω and 50Ω. Proper
high-frequency bypassing (C1) should be used for the
bias voltage to eliminate power-supply noise from
entering the tank.
Figure 2. Oscillator Tank Schematic, Using the On-Chip VCO
f =
r
C =
EFF
1
C2
1
π
2L3C
()( )
EFF
1
1
++
2
CC
3
D
1
+
26
C
MAX2440
MAX2441
MAX2442
V
CC
L4
100nH
TANK
L
T
L
T
TANK
SEE FIGURE 1 FOR R6, R7, C2, C3, C26, AND L3 COMPONENT VALUES.
R7
L3
R6
C26
R5
1k
C2
1/2 D1
R8
47k
C3
1/2 D1
R4
1k
D1 = ALPHA SMV1299-004
VCO_CTRL
C1
47pF
Oscillator-Tank PC Board Layout
The parasitic PC board capacitance, as well as PCB
trace inductance and package inductance, can 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
will reduce 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 3). 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, TANK and TANK
must be pulled up to the V
CC
supply via 50Ω resistors.
If a differential LO source such as the MAX2620 is
available, AC couple the inverting output into TANK.
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
______________________________________________________________________________________ 11
MAX2440/MAX2441/MAX2442
Figure 3. Using an External Local Oscillator
TRANSISTOR COUNT: 2802
Figure 4. Series Coupled Resonant Tank for Wide Tuning Range and Low Phase Noise
Chip Information
V
CC
MAX2440
MAX2441
MAX2442
TANK
TANK
MAX2440
MAX2441
MAX2442
50Ω
50Ω
C
BLOCK
0.01µF
V
CC
EXTERNAL LO LEVEL IS
0dBm FROM A 50Ω
SOURCE.
L
T
TANK
EXT LO
L1
L3
R1
Ci
L
T
TANK
1/2 D1
R2
1/2 D1
L2
L4
L5
R3
VTUNE
C2
V
CC
C1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX2440/MAX2441/MAX2442
900MHz Image-Reject Receivers
Package Information
Functional Diagram
LNAGAIN
RXIN
CAP1
RXON
BIAS
MAX2440
MAX2441
MAX2442
PHASE
SHIFTER
90°
0°
90°0°
Σ
÷1/64/65
RXOUT
DIV1
MOD
PREOUT
PREGND
TANK
TANK
VCOON
SSOP.EPS
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