MAX2424EAI [MAXIM]
900MHz Image-Reject Receivers with Transmit Mixer; 900MHz的图像抑制接收器与发射混频器
| 型号： | MAX2424EAI |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 900MHz Image-Reject Receivers with Transmit Mixer |
| 文件： | 总14页 (文件大小：164K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1350 Rev 2; 2/99
900MHz Image-Reject Receivers
with Transmit Mixer
/MAX426
________________General Description
____________________________Features
♦ Receive Mixer with 35dB Image Rejection
♦ Adjustable-Gain LNA
The MAX2424/MAX2426 highly integrated front-end ICs
provide the lowest cost solution for cordless and ISM-
band radios operating in the 900MHz band. Both devices
incorporate a receive image-reject mixer (to reduce filter
cost) as well as a versatile transmit mixer. The devices
operate from a +2.7V to +4.8V single power supply,
allowing direct connection to a 3-cell battery stack.
♦ Up to +2dBm Combined Receiver Input IP3
♦ 4dB Combined Receiver Noise Figure
♦ Optimized for Common Receiver IF Frequencies:
10.7MHz (MAX2424)
The receive 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 (IIP3) of up to +2dBm.
70MHz (MAX2426)
♦ PA Predriver Provides up to 0dBm
♦ Low Current Consumption: 23mA Receive
20mA Transmit
The transmitter consists of a double-balanced mixer and
a power amplifier (PA) predriver that produces up to
0dBm (in some applications serving as the final power
stage). It can be used in a variety of configurations,
including BPSK modulation, direct VCO modulation, and
transmitter upconversion. For devices featuring trans-
mit as well as receive image rejection, refer to the
MAX2420/MAX2421/MAX2422/MAX2460/MAX2463
data sheet.
9.5mA Oscillator
♦ 0.5µA Shutdown Mode
♦ Operates from Single +2.7V to +4.8V Supply
_______________Ordering Information
PART
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
MAX2424EAI
MAX2426EAI
28 SSOP
The MAX2424/MAX2426 have an on-chip local oscillator
(LO), requiring only an external varactor-tuned LC tank
for operation. The integrated divide-by-64/65 dual-mod-
ulus prescaler can also be set to a direct mode, in which
it acts as an LO buffer amplifier. Four separate power-
down inputs can be used for system power manage-
ment, including a 0.5µA shutdown mode.
28 SSOP
___________________Pin Configuration
The MAX2424/MAX2426 come in a 28-pin SSOP pack-
age.
TOP VIEW
V
28
27
26
25
24
23
22
21
GND
GND
GND
CC
1
2
3
4
5
6
7
8
9
________________________Applications
Cordless Phones
CAP1
RXOUT
GND
TANK
TANK
Wireless Telemetry
RXIN
MAX2424
MAX2426
Wireless Networks
V
CC
V
CC
V
Spread-Spectrum Communications
Two-Way Paging
GND
GND
CC
PREOUT
20 PREGND
19
TXOUT
MOD
18 DIV1
LNAGAIN 10
V
CC
11
12
13
14
VCOON
17
16
15
TXIN
TXIN
RXON
TXON
Functional Diagram appears at end of data sheet.
CAP2
SSOP
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
900MHz Image-Reject Receiver
with Transmit Mixer
ABSOLUTE MAXIMUM RATINGS
V
to GND...........................................................-0.3V to +5.5V
Continuous Power Dissipation (T = +70°C)
A
CC
TXIN, TXIN Differential Voltage..............................................+2V
SSOP (derate 9.50mW/°C above +70°C) ......................762mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +165°C
Lead Temperature (soldering, 10sec) .............................+300°C
Voltage on TXOUT......................................-0.3V to (V
Voltage on LNAGAIN, TXON, RXON, VCOON,
DIV1, MOD, TXIN, TXIN............................-0.3V to (V
+ 1.0V)
CC
+ 0.3V)
CC
RXIN Input Power..............................................................10dBm
TANK, TANK Input Power...................................................2dBm
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.
DC ELECTRICAL CHARACTERISTICS
(V
CC
= +2.7V to +4.8V, no RF signals applied, LNAGAIN = Unconnected, V
= V
= 2.3V, V = 2.4V, V
VCOON
= V
=
RXON
TXON
TXIN
TXIN
V
MOD
= V
= 0.45V, PREGND = GND, T = -40°C to +85°C. Typicals are at T = +25°C, V
= 3.3V, unless otherwise noted.)
DIV1
A
A
CC
/MAX426
PARAMETER
CONDITIONS
MIN
TYP
MAX
4.8
UNITS
V
Supply-Voltage Range
2.7
Oscillator Supply Current
PREGND = unconnected
9.5
4.2
14
mA
Prescaler Supply Current
(÷ 64/65 mode) (Note 1)
6
mA
Prescaler Supply Current
(buffer mode) (Note 2)
V
= 2.4V
5.4
23
8.5
36
32
mA
mA
mA
DIV1
Receive Supply Current (Note 3)
V
V
= 2.4V, PREGND = unconnected
RXON
= 0.45V, V
= 2.4V,
TXON
RXON
Transmitter Supply Current (Note 4)
20
PREGND = unconnected
T = +25°C
0.5
A
VCOON = RXON = TXON
= MOD = DIV1 = GND
Shutdown Supply Current
µA
T = -40°C to +85°C
A
10
Digital Input Voltage High
Digital Input Voltage Low
Digital Input Current
RXON, TXON, DIV1, VCOON, MOD
RXON, TXON, DIV1, VCOON, MOD
Voltage on any one digital input = V
2.4
V
V
0.45
10
or GND
1
µA
CC
Note 1: Calculated by measuring the combined oscillator and prescaler supply current and subtracting the oscillator supply current.
Note 2: Calculated by measuring the combined oscillator and LO buffer supply current and subtracting the oscillator supply current.
Note 3: 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.
Note 4: Calculated by measuring the combined transmit and oscillator supply current and subtracting the oscillator supply current.
2
_______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
/MAX426
AC ELECTRICAL CHARACTERISTICS
(MAX2424/MAX2426 EV kit, V
= +3.3V, f
= 915MHz, P
= -35dBm, V
= V
= 2.3V (DC bias), V = 250mVp-p,
TXIN
CC
RXIN
RXIN
TXIN
TXIN
f
= 1MHz, V
= 2V, V
= 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, T = +25°C, unless otherwise noted.)
A
VCOON
TXIN
LNAGAIN
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
RECEIVER (V = 2.4V, f = 925.7MHz (MAX2424), f = 985MHz (MAX2426))
RXON
LO
LO
Input Frequency Range
(Notes 5, 6)
800
1000
MHz
MAX2424 (Notes 5, 6)
MAX2426 (Notes 5, 6)
8.5
55
26
20
19
19
18
10.7
70
12.5
85
IF Frequency Range
MHz
dB
Image Frequency Rejection
35
MAX2424
MAX2426
MAX2424
MAX2426
22
24.5
23.5
25
V
= V
,
LNAGAIN
CC
T
A
= +25°C (Note 7)
21
V
= V
,
LNAGAIN
CC
Conversion Power Gain
Noise Figure
dB
T
A
= -40°C to +85°C (Notes 5, 7)
24
V
= 1V (Note 7)
12
-16
4
LNAGAIN
LNAGAIN = GND (Note 7)
LNAGAIN = V (Notes 5, 7)
5
CC
dB
dB
V
= 1V (Notes 5, 7)
12
LNAGAIN
LNAGAIN = V (Notes 5, 8)
-19
-17
-8
CC
Input Third-Order Intercept
(IIP3)
V
= 1V (Notes 5, 8)
LNAGAIN
LNAGAIN = V
-26
-18
-60
500
CC
Input 1dB Compression
dBm
V
= 1V
LNAGAIN
LO to RXIN Leakage
Receiver on or off
(Note 9)
dBm
ns
Receiver Turn-On Time
TRANSMITTER (V
= 2.4V, f = 915MHz)
LO
TXON
Output Frequency Range
(Notes 5, 10)
800
1000
MHz
MHz
dBm
dBm
dBm
Baseband 3dB Bandwidth
Output Power
125
-7
T
T
= +25°C
-9.5
-10
-5
A
= T
to T
(Note 5)
-4.5
A
MIN
MAX
Output 1dB Compression
Output Third-Order Intercept (OIP3)
-0.5
3.5
(Note 11)
(Note 12)
Carrier Suppression
30
dBc
dBm/Hz
ns
Output Noise Density
Transmitter Turn-On Time
-140
220
_______________________________________________________________________________________
3
900MHz Image-Reject Receiver
with Transmit Mixer
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2424/MAX2426 EV kit, V
= +3.3V, f
= 915MHz, P
= -35dBm, V
= V
= 2.3V (DC bias), V = 250mVp-p,
TXIN
CC
RXIN
RXIN
TXIN
TXIN
f
= 1MHz, V
= 2V, V
= 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, T = +25°C, unless otherwise noted.)
A
VCOON
TXIN
LNAGAIN
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OSCILLATOR AND PRESCALER
Oscillator Frequency Range
(Note 5)
800
1100
MHz
MAX2424
MAX2426
MAX2424
MAX2426
MAX2424
MAX2426
82
72
8
Oscillator Phase Noise
10kHz offset (Note 13)
dBc/Hz
Standby to TX or Standby to RX
35
70
110
500
-8
Oscillator Pulling
kHz
RX to TX with P
=-45dBm (RX mode)
RXIN
to P
= 0dBm (TX mode) (Note 14)
RXIN
Prescaler Output Level
mVp-p
dBm
Z = 100kΩ | | 10pF
L
= 2.4V,
T
T
= +25°C
-11
-12
Oscillator Buffer Output Level
(Notes 5, 13)
A
V
DIV1
Z = 50Ω
L
= -40°C to +85°C
A
/MAX426
Required Modulus Setup Time
(Notes 5, 15)
÷ 64/65 mode
÷ 64/65 mode
10
0
ns
ns
Required Modulus Hold Time
(Notes 5, 15)
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 a plot showing Receiver Gain vs. LNAGAIN Voltage, Input IP3 vs.
LNAGAIN Voltage, and Noise Figure vs. LNAGAIN Voltage.
Note 8: Two tones at P
= -45dBm each, f1 = 915.0MHz and f2 = 915.2MHz.
RXIN
Note 9: Time delay from V
= 0.45V to V
= 2.4V transition to the time the output envelope reaches 90% of its final value.
RXON
RXON
Note 10: Output power typically falls to -10dBm at the frequency extremes.
Note 11: Two tones at V = 125mVp-p, f1 = 1.0MHz, and f2 = 1.2MHz.
TXIN
Note 12: Time delay from V
= 0.45V to V
= 2.4V transition to the time the output envelope reaches 90% of its final value.
TXON
TXON
Note 13: Using tank components L3 = 5.0nH (Coilcraft A02T), C2 = C3 = C26 = 3.3pF, R6 = R7 = 10Ω.
Note 14: This approximates a typical application in which TXOUT is followed by an external PA and a T/R switch with finite isolation.
Note 15: Relative to the rising edge of PREOUT.
4
_______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
/MAX426
__________________________________________Typical Operating Characteristics
(MAX2424/MAX2426 EV kit, V
= +3.3V; f
= 925.7MHz (MAX2424), 985MHz (MAX2426); f
= 915MHz, P
=
RXIN
CC
RX)
RXIN
LO(
-35dBm, f
= 915MHz, V
= V
= 2.3V (DC bias), V
= 250mVp-p, f
= 1MHz, V
= 2V, V
= 2.4V,
LO(TX)
TXIN
TXIN
TXIN
TXIN
LNAGAIN
VCOON
RXON = TXON = MOD = DIV1 = PREGND = GND, T = +25°C, unless otherwise noted.)
A
RECEIVER SUPPLY CURRENT
vs. TEMPERATURE
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
TRANSMITTER SUPPLY CURRENT
vs. TEMPERATURE
42
40
38
36
34
32
30
28
26
24
4.5
39
37
35
33
31
V
CC
= 4.8V
VCOON = GND
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
V
CC
= 3.3V
V
CC
= 4.8V
V
= 2.7V
CC
V
= 3.3V
CC
29
27
25
23
21
V
CC
= 4.8V
V
CC
= 2.7V
RXON = V
CC
V
CC
= 3.3V
TXON = V
CC
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
V
CC
= 2.7V
-40 -20
0
20
40
60
80
-40 -20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
RECEIVER NOISE FIGURE
vs. LNAGAIN
RECEIVER GAIN vs. LNAGAIN
RECEIVER INPUT IP3 vs. LNAGAIN
40
35
30
25
20
15
10
5
25
20
15
10
5
5
LNA
PARTIALLY
BIASED
LNA
OFF
LNA
PARTIALLY
BIASED
ADJUSTABLE MAX
LNA
OFF
LNA
PARTIALLY
BIASED
ADJUSTABLE MAX
LNA
OFF
GAIN
GAIN
GAIN
GAIN
0
AVOID
THIS
REGION
-5
ADJUSTABLE MAX
GAIN GAIN
0
-10
-15
-20
-5
RXON = V
CC
CC
AVOID
THIS
REGION
DIV1 = V
-10
-15
-20
AVOID
THIS
REGION
RXON = V
1.5
RXON = V
CC
CC
0
0
0.5
1.0
1.5
2.0
0
0.5
1.0
2.0
0
0.5
1.0
1.5
2.0
LNAGAIN VOLTAGE (V)
LNAGAIN VOLTAGE (V)
LNAGAIN VOLTAGE (V)
MAX2424
RECEIVER GAIN vs. TEMPERATURE
RECEIVER NOISE FIGURE vs.
TEMPERATURE AND SUPPLY VOLTAGE
RECEIVER INPUT IP3
vs. TEMPERATURE
5.5
5.0
4.5
-6
-8
LNAGAIN = V
CC
LNAGAIN = V
CC
26
24
22
20
18
RXON = V
RXON = V
V
= 1V
CC
CC
CC
LNAGAIN
DIV1 = V
V
= 4.8V
CC
-10
-12
-14
V
CC
= 4.8V
V
= 3.3V
CC
V
= 2.7V
CC
4.0
V
= 3.3V
CC
V
= 2.7V
CC
-16
V
= 2V
LNAGAIN
3.5
3.0
-18
-20
RXON = V
CC
-40 -20
0
20
40
60
80
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
900MHz Image-Reject Receiver
with Transmit Mixer
______________________________Typical Operating Characteristics (continued)
(MAX2424/MAX2426 EV kit, V
= +3.3V; f
= 925.7MHz (MAX2424), 985MHz (MAX2426); f
= 915MHz, P
=
RXIN
CC
RX)
RXIN
LO(
-35dBm, f
= 915MHz, V
= V
= 2.3V (DC bias), V
= 250mVp-p, f
= 1MHz, V
= 2V, V
= 2.4V,
LO(TX)
TXIN
TXIN
TXIN
TXIN
LNAGAIN
VCOON
RXON = TXON = MOD = DIV1 = PREGND = GND, T = +25°C, unless otherwise noted.)
A
MAX2424
RECEIVER OUTPUT 1dB
COMPRESSION POINT vs. TEMPERATURE
RECEIVER IMAGE REJECTION
vs. RF FREQUENCY
RECEIVER IMAGE REJECTION
vs. IF FREQUENCY
60
50
40
30
20
10
0
40
35
-3
-4
RXON = V
CC
MAX2424
MAX2426
V
CC
= 4.8V
30
25
20
15
10
5
-5
-6
-7
-8
-9
V
= 2.7V
CC
V
= 3.3V
CC
-10
-20
RXON = V
60
CC
RXON = V
CC
/MAX426
0
1
-40 -20
0
20
40
80
0
400
800
1200
1600
2000
10
100
1000
TEMPERATURE (°C)
RF FREQUENCY (MHz)
IF FREQUENCY (MHz)
RXIN INPUT IMPEDANCE
vs. FREQUENCY
TRANSMITTER OUTPUT POWER
vs. INPUT VOLTAGE
TRANSMITTER OUTPUT POWER
vs. TEMPERATURE
MAX2424/6-13
5
50
45
40
35
30
25
20
15
10
5
-100
-80
-60
-40
-2
-3
TXON = V
RXON = V
V
= 4.8V
CC
CC
CC
0
-5
V
= 3.3V
-4
CC
-5
-6
IMAGINARY
REAL
V
CC
= 4.8V
V
CC
= 2.7V
-7
-10
-15
-20
-25
-8
-9
V
CC
= 2.7V
V
CC
= 3.3V
-10
-11
-12
-13
-14
-20
0
TXON = V
CC
0
600
800
1000
1200
1400
10
100
INPUT VOLTAGE (mVp-p)
1000
-20
20
TEMPERATURE (°C)
-40
0
40
60
80
FREQUENCY (MHz)
TRANSMITTER 1dB COMPRESSION POINT
vs. TEMPERATURE
TXOUT OUTPUT IMPEDANCE
vs. FREQUENCY
TRANSMITTER OUTPUT SPECTRUM
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
1
0
150
100
50
DOUBLE-SIDE
BAND
FUNDAMENTAL
TXON = V
CC
V
CC
= 4.8V
REAL
-1
-2
-3
-4
-5
-6
-7
0
LO
V
CC
= 3.3V
-50
IMAGINARY
-100
-150
-200
-250
-300
V
CC
= 2.7V
TXON = V
TXON = V
CC
CC
910 911 912 913 914 915 916 917 918 919 920
FREQUENCY (MHz)
-40 -20
0
20
40
60
80
600 800 1000 1200 1400 1600 1800 2000
FREQUENCY (MHz)
TEMPERATURE (°C)
6
_______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
/MAX426
______________________________Typical Operating Characteristics (continued)
(MAX2424/MAX2426 EV kit, V
= +3.3V; f
= 925.7MHz (MAX2424), 985MHz (MAX2426); f
= 915MHz, P
=
RXIN
CC
RX)
RXIN
LO(
-35dBm, f
= 915MHz, V
= V
= 2.3V (DC bias), V
= 250mVp-p, f
= 1MHz, V
= 2V, V
= 2.4V,
LO(TX)
TXIN
TXIN
TXIN
TXIN
LNAGAIN
VCOON
RXON = TXON = MOD = DIV1 = PREGND = GND, T = +25°C, unless otherwise noted.)
A
TRANSMITTER BASEBAND
FREQUENCY RESPONSE
POWER vs. TXIN VOLTAGE
3
0
-3
-6
-9
-12
-15
-18
-21
-24
-27
-30
-33
-36
10
0
TXON = V
CC
NOTE: TXIN IS TOTAL
VOLTAGE FOR TWO TONES
(PEAK-TO-PEAK)
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
FUNDAMENTAL
IM3 LEVEL
TXON = V
CC
1
10
100
1000
10
100
TXIN VOLTAGE (mVp-p)
1000
FREQUENCY (MHz)
______________________________________________________________Pin Description
PIN
NAME
FUNCTION
Supply-Voltage Input for Master Bias Cell. Bypass with a 47pF low-inductance capacitor and 0.1µF to
GND (pin 28 recommended).
1
V
CC
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.
2
CAP1
3
4
RXOUT
GND
Single-ended, 330Ω IF Output. AC couple to this pin.
Ground Connection
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.
5
6
RXIN
Supply Voltage Input for the Receive Low-Noise Amplifier. Bypass with a 47pF low-inductance capacitor
to GND (pin 7 recommended).
V
CC
Ground Connection for Receive Low-Noise Amplifier. Connect directly to ground plane using multiple
vias.
7
8
9
GND
GND
Ground Connection for Signal-Path Blocks, except LNA
PA Predriver Output. See Figure 1 for an example matching network, which provides better than 2:1
VSWR from 902MHz to 928MHz.
TXOUT
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.
10
11
LNAGAIN
Supply Voltage Input for the Signal-Path Blocks, except LNA. Bypass with a 47pF low-inductance capac-
itor and 0.01µF to GND (pin 8 recommended).
V
CC
_______________________________________________________________________________________
7
900MHz Image-Reject Receiver
with Transmit Mixer
_________________________________________________Pin Description (continued)
PIN
NAME
FUNCTION
Transmit Mixer’s Noninverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input
port. See Figure 1.
12
TXIN
Transmit Mixer’s Inverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port.
See Figure 1.
13
14
15
16
17
TXIN
CAP2
Transmit Bias Compensation Input. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND.
Do not make any other connections to this pin.
Drive TXON and VCOON with a logic high to enable the transmit IF variable-gain amplifier, upconverter
mixer, and PA predriver. See Power Management section.
TXON
RXON
VCOON
Drive RXON and VCOON with a logic high to enable the LNA, receive mixer, and IF output buffer.
See Power Management section.
Drive VCOON with a logic high to turn on the VCO, phase shifters, VCO buffers, and prescaler. To dis-
able the prescaler, leave the PREGND pin unconnected.
/MAX426
Drive DIV1 with a logic high to disable the divide-by-64/65 prescaler and connect the PREOUT pin
directly to an oscillator buffer amplifier, which outputs -8dBm into a 50Ω load. Drive DIV1 low for divide-
by-64/65 operation. Drive this pin low when in shutdown to minimize shutdown current.
18
19
20
DIV1
MOD
Modulus Control for the Divide-by-64/65 Prescaler. Drive MOD high for divide-by-64 mode. Drive MOD
low for divide-by-65 mode.
Ground connection for the Prescaler. Connect PREGND to ground for normal operation. Leave uncon-
nected to disable the prescaler and the output buffer. Connect MOD and DIV1 to ground and leave PRE-
OUT unconnected when disabling the prescaler.
PREGND
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.
21
PREOUT
Supply-Voltage Input for Prescaler. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND
(pin 20 recommended).
22
23
24
25
V
V
CC
Supply-Voltage Input for VCO and Phase Shifters. Bypass with a 47pF low-inductance capacitor to GND
(pin 26 recommended).
CC
Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using
an external oscillator.
TANK
Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using
an external oscillator.
TANK
26
27
28
GND
GND
GND
Ground Connection for VCO and Phase Shifters
Ground (substrate)
Ground Connection for Master Bias Cell
8
_______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
/MAX426
V
V
CC
CC
1
22
V
V
CC
CC
47pF
0.01µF
0.1µF
0.1µF
47pF
20
23
28
2
GND
PREGND
VCO TANK COMPONENTS
FOR 915MHz RF FREQUENCY
V
CC
L3
(nH)
C26
(pF)
CAP1
C2, C3
(pF)
R6, R7
(Ω)
V
CC
DEVICE
47pF
47pF
26
27
6.8
3.3
2.0
4.0
MAX2424
MAX2426
3.3
8.0
10
20
GND
GND
RECEIVE
RF INPUT
8.2nH
MAX2424
MAX2426
5
0.01µF
RXIN
3
RXOUT
RECEIVE IF OUTPUT (330Ω)
47pF
12nH
V
CC
0.01µF*
47pF
MODULATOR INPUT
22nH
12
13
TXIN
TXIN
47pF
10k
9
V
CC
TXOUT
R
A
R
B
18nH
TRANSMIT
RF OUTPUT
10k
MODULATOR INPUT
0.01µF*
V
CC
6
7
VARACTORS:
V
CC
ALPHA SMV1299-004
OR EQUIVALENT
1k
47pF
100nH
GND
V
R7
CC
25
24
11
8
TANK
C2
47k
C26
V
CC
VCO
0.01µF
0.01µF
47pF
L3
ADJUST
R6
GND
47pF
TANK
1000pF
1k
C3
14
21
19
CAP2
PREOUT
MOD
TO PLL
MOD
47pF
18
17
DIV1
DIV1
VCOON
VCOON
*
WHEN USING DIFFERENTIAL
SOURCE, REMOVE RESISTORS
10
4
16
15
LNAGAIN
GND
LNAGAIN
RXON
TXON
RXON
TXON
AND REPLACE CAPACITORS WITH
SHORTS. FOR SINGLE-ENDED
47pF
SOURCE, DRIVE ONLY MODULATOR
INPUT. CHOOSE R AND R VALUES
A
B
AS SHOWN IN TRANSMITTER SECTION.
Figure 1. Typical Operating Circuit
_______________________________________________________________________________________
9
900MHz Image-Reject Receiver
with Transmit Mixer
_______________Detailed Description
The following sections describe each of the functional
blocks shown in the Functional Diagram.
MAX2424
MAX2426
Receiver
TXIN
The MAX2424/MAX2426’s receive path consists of a
900MHz low-noise amplifier, an image-reject mixer, and
an IF buffer amplifier.
1.5µA
1.5µA
2M
VMIXER INPUT
The LNA’s gain and biasing are adjustable via the LNA-
GAIN pin. Proper operation of this pin provides optimum
TXIN
performance over a wide range of signal levels. The LNA
has four modes determined by the DC voltage applied on
the LNAGAIN pin. See Table 1, as well as the relevant
Figure 2. TXIN, TXIN Equivalent Circuit
Typical Operating Characteristics plots.
At low LNAGAIN voltages, the LNA is shut off and the
input signal capacitively couples directly into mixer to
provide maximum linearity for large-signal operation
(receiver close to transmitter). As the LNAGAIN voltage
increases, the LNA turns 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 applica-
tions where linearity is a concern. As the LNAGAIN volt-
age reaches 1V, the LNA is fully biased into Class A
mode, and the gain is monotonically adjustable for LNA-
GAIN voltages above 1V. See the receiver gain, IP3, and
Noise Figure vs. LNAGAIN plots in the Typical Operating
Characteristics for more information.
each mixer. An on-chip oscillator and an external tank
circuit generates the LO. Its signal is buffered and split
into two phase shifters, which provide 90° of phase shift
across their outputs. This pair of LO signals is fed to the
mixers. The mixers’ outputs then pass through a sec-
ond 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.
/MAX426
Transmitter
The MAX2424/MAX2426 transmitter consists of a bal-
anced mixer and a PA driver amplifier. The mixer inputs
are accessible via the TXIN and TXIN pins. An equiva-
lent circuit for the TXIN and TXIN pins is shown in
Figure 2. Because TXIN and TXIN are linearly coupled
to the mixer stage, they can accept spectrally shaped
input signals. Typically, the mixer can be used to multi-
ply the LO with a baseband signal, generating BPSK or
ASK modulation. Transmit upconversion can also be
implemented by applying a modulated IF signal to
these inputs. For applications requiring image rejection
on the transmitter, refer to the MAX2420/MAX2421/
MAX2422/MAX2460/MAX2463 data sheet.
The downconverter is implemented using an image-
reject mixer consisting of an input buffer with two out-
puts, each of which is fed to a double-balanced mixer.
A quadrature LO drives the local-oscillator (LO) port of
Table 1. LNA Modes
LNAGAIN
MODE
VOLTAGE (V)
LNA capacitively bypassed,
minimum gain, maximum IP3
0 < V
≤ 0.5
LNAGAIN
LNA partially biased. Avoid this
mode— the LNA operates in a
Class C manner
0.5 < V
< 1.0
LNAGAIN
Set the common-mode voltage at TXIN, TXIN to 2.3V by
selecting appropriate values for R and R (Figure 1). The
A
B
total series impedance of R and R should be approxi-
A
B
LNA gain is monotonically
adjustable
1.0 < V
≤ 1.5
LNAGAIN
LNAGAIN
mately 100kΩ.
Frequency modulation (FM) is realized by modulating
the VCO tuning voltage. Apply the appropriate differen-
tial and common-mode voltages to TXIN and TXIN to
control transmitter output power (Figure 3).
LNA at maximum gain
(remains monotonic)
1.5 < V
≤ V
CC
10 ______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
/MAX426
Phase Shifter
The MAX2424/MAX2426 uses passive networks to pro-
vide quadrature phase shifting for the receive IF and LO
signals. Because these networks are frequency selec-
tive, both the RF and IF frequency operating ranges are
limited. Image rejection degrades as the IF and RF
moves away from the designed optimum frequencies.
The MAX2424/MAX2426’s phase shifters are arranged
such that the LO frequency is higher than the RF carrier
frequency (high-side injection).
V
CC
MAX2424
MAX2426
R1
R2
R3
i
1.5µA
TXIN
TXIN
2M
Local Oscillator (LO)
The on-chip LO is formed by an emitter-coupled differ-
ential pair. An external LC resonant tank sets the oscil-
lation frequency. A varactor diode is typically used to
create a voltage-controlled oscillator (VCO). See the
Applications Information section for an example VCO
tank circuit.
1.5µA
R = R + R + R
T
1
2
3
V
= V
- V
DIFF
TXIN TXIN
Figure 3. Biasing TXIN and TXIN for FM
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
For example, if V
T
that bias currents for TXIN and TXIN have little effect
over temperature. Set V
mode voltage range requirements at V
= 3.3V and P
= -8dBm, choose
CC
OUT
R = 100kΩ for sufficient current through the divider, so
= 2.3V to satisfy common-
TXIN
and TANK require pull-up resistors to V . See the
CC
= 3.3V.
CC
Applications Information section for details.
Use the Transmit Output Power vs. Input Voltage graph
in the Typical Operating Characteristics to determine
the input voltage (in mVp-p) required to produce the
desired output. Divide this value by 2√2 and use it for
The local oscillator resists pulling caused by changes
in load impedance that occur as the part is switched
from standby mode, with just the oscillator running to
either transmit or receive mode. The amount of LO
pulling is affected if a signal is present at the RXIN port
in transmit mode. The most common cause of pulling is
imperfect isolation in an external transmit/
receive (T/R) switch. The AC Electrical Characteristics
table contains specifications for this case as well.
V
. A -8dBm transmitter output requires 250mVp-p /
DIFF
2√2 = 88.4mV.
V
= 2.3V + 0.0884V = 2.3884V
TXIN
R = R1 + R2 + R3
T
Solve for resistors R1, R2, and R3 with the following
equations:
Prescaler
The on-chip prescaler operates in two different modes:
as a dual-modulus divide-by-64/65, or as an 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.
V
x R
TXIN
T
R3 =
R2 =
V
CC
R
T
V
– V
x
TXIN
TXIN
(
)
V
CC
R1 = R – R2 – R3
T
Since the transmit and receive sections typically require
different LO frequencies, it is not recommended to have
both transmit and receive active at the same time.
In divide-by-64/65 drive mode, the division ratio is con-
trolled by the MOD pin. Drive MOD high to operate the
prescaler in divide-by-64 mode. Drive MOD and DIV1
low to operate the prescaler in divide-by-65 mode.
______________________________________________________________________________________ 11
900MHz Image-Reject Receiver
with Transmit Mixer
To disable the prescaler entirely, leave PREGND and
PREOUT unconnected. Also connect the MOD and
DIV1 pins to GND. Disabling the prescaler does not
affect operation of the VCO stage.
Choose tank components according to your application
needs, such as phase-noise requirements, tuning
range, and VCO gain. High Q inductors such as air-
core micro springs yield low phase noise. Use a low-
tolerance 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
Power Management
The MAX2424/MAX2426 supports four 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. Stabilize VCO by powering it up
prior to transmitting or receiving. For transmit-to-receive
switching, the receiver and transmitter sections have
their own enable control inputs, RXON and TXON. 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. The TXON input enables the upcon-
verter mixer and PA predriver. VCOON must be high for
the transmitter to operate. When TXON is low, the trans-
mitter is off.
series package inductance L . Keep R6 and R7 as
T
small as possible to minimize phase noise, yet large
enough to ensure oscillator start-up in fundamental
mode. Oscillator start-up with 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.
/MAX426
To disable all chip functions and reduce the supply cur-
rent to typically 0.5µA, pull VCOON, DIV1, MOD, RXON,
and TXON low.
V
CC
L4
___________Applications Information
100nH
MAX2424
MAX2426
R5
1k
Oscillator Tank
The on-chip oscillator requires a parallel-resonant tank
circuit connected across TANK and TANK. Figure 4
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 capaci-
tors C2, C3, and both halves of the varactor diode
capacitance set the resonant frequency as follows:
C2
R7
TANK
1/2 D1
R8
VCO_CTRL
47k
L3
6.8nH
C26
C3
C1
47pF
R6
1/2 D1
1
TANK
R4
1k
f =
r
2π L3 C
(
)
(
)
EFF
D1 = ALPHA SMV1299-004
1
C
=
+ C26
SEE FIGURE 1 FOR R6, R7, C2, C3, C26, AND L3 COMPONENT VALUES.
EFF
1
1
2
C
D1
+
+
C2 C3
Figure 4. Oscillator Tank Schematic Using the On-Chip VCO
where C is the capacitance of one varactor diode.
D1
12 ______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
/MAX426
L
T
TANK
L1
L3
R1
MAX2424
MAX2426
1/2 D1
1/2 D1
R2
L4
V
TUNE
V
CC
C
i
C2
C1
L
T
L2
L5
R3
TANK
Figure 5. Series-Coupled Resonant Tank for Wide Tuning Range and Low Phase Noise
For applications that require a wide tuning range and
low phase noise, a series-coupled resonant tank may
be required as shown in Figure 5. This tank will use the
V
V
CC
package inductance in series with inductors L1, L2,
and capacitance of varactor D1 to set the net equiva-
lent 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 cho-
sen 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 0 and 50Ω. Proper
high frequency bypassing (C1) should be used for the
bias voltage to eliminate power supply noise from
entering the tank.
MAX2424
50Ω
50Ω
47pF
TANK
CC
50Ω
EXT LO
TANK
EXTERNAL LO LEVEL IS 0dBm
FROM A 50Ω SOURCE.
50Ω
47pF
Oscillator Tank PC Board Layout
The parasitic PC board capacitance, as well as PCB
trace inductance and package inductance, affect oscil-
lation 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
reduces parasitic capacitance.
Figure 6. Using an External Local Oscillator
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 6). 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, pull up the TANK
and TANK pins to the V
supply via 50Ω resistors.
CC
If a differential LO source such as the MAX2620 is
available, AC-couple the inverting output into TANK.
______________________________________________________________________________________ 13
900MHz Image-Reject Receiver
with Transmit Mixer
_________________________________________________________Functional Diagram
LNAGAIN
90°
RXOUT
Σ
RXIN
0°
DIV1
MOD
CAP1
0°
90°
÷ 1/64/65
PREOUT
RXON
TXON
BIAS
PREGND
TANK
CAP2
PHASE
SHIFTER
TANK
VCOON
0°
MAX2424
MAX2426
/MAX426
TXIN
TXOUT
TXIN
________________________________________________________Package Information
14 ______________________________________________________________________________________
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