Maxim MAX2424EAI 900mhz image-reject receivers with transmit mixer Datasheet

19-1350 Rev 2; 2/99
L
MANUA
ION KIT HEET
T
A
U
L
EVA
TA S
WS DA
FOLLO
900MHz Image-Reject Receivers
with Transmit Mixer
____________________________Features
♦ Receive Mixer with 35dB Image Rejection
________________________Applications
Cordless Phones
Wireless Telemetry
♦ Adjustable-Gain LNA
♦ Up to +2dBm Combined Receiver Input IP3
♦ 4dB Combined Receiver Noise Figure
♦ Optimized for Common Receiver IF Frequencies:
10.7MHz (MAX2424)
70MHz (MAX2426)
♦ PA Predriver Provides up to 0dBm
♦ Low Current Consumption: 23mA Receive
20mA Transmit
9.5mA Oscillator
♦ 0.5µA Shutdown Mode
♦ Operates from Single +2.7V to +4.8V Supply
_______________Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX2424EAI
-40°C to +85°C
28 SSOP
MAX2426EAI
-40°C to +85°C
28 SSOP
___________________Pin Configuration
TOP VIEW
VCC 1
28 GND
CAP1 2
27 GND
RXOUT 3
26 GND
GND 4
25 TANK
RXIN 5
Wireless Networks
VCC 6
MAX2424
MAX2426
24 TANK
23 VCC
Spread-Spectrum Communications
GND 7
Two-Way Paging
GND 8
21 PREOUT
TXOUT 9
20 PREGND
Functional Diagram appears at end of data sheet.
22 VCC
LNAGAIN 10
19 MOD
VCC 11
18 DIV1
TXIN 12
17 VCOON
TXIN 13
16 RXON
CAP2 14
15 TXON
SSOP
________________________________________________________________ Maxim Integrated Products
1
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For small orders, phone 1-800-835-8769.
MAX2424/MAX2426
________________General Description
The MAX2424/MAX2426 highly integrated front-end ICs
provide the lowest cost solution for cordless and ISMband 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.
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.
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 transmit as well as receive image rejection, refer to the
MAX2420/MAX2421/MAX2422/MAX2460/MAX2463
data sheet.
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-modulus prescaler can also be set to a direct mode, in which
it acts as an LO buffer amplifier. Four separate powerdown inputs can be used for system power management, including a 0.5µA shutdown mode.
The MAX2424/MAX2426 come in a 28-pin SSOP package.
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
ABSOLUTE MAXIMUM RATINGS
VCC to GND ...........................................................-0.3V to +5.5V
TXIN, TXIN Differential Voltage ..............................................+2V
Voltage on TXOUT......................................-0.3V to (VCC + 1.0V)
Voltage on LNAGAIN, TXON, RXON, VCOON,
DIV1, MOD, TXIN, TXIN............................-0.3V to (VCC + 0.3V)
RXIN Input Power..............................................................10dBm
TANK, TANK Input Power ...................................................2dBm
Continuous Power Dissipation (TA = +70°C)
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
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
(VCC = +2.7V to +4.8V, no RF signals applied, LNAGAIN = Unconnected, VTXIN = V TXIN = 2.3V, VVCOON = 2.4V, VRXON = VTXON =
VMOD = VDIV1 = 0.45V, PREGND = GND, TA = -40°C to +85°C. Typicals are at TA = +25°C, VCC = 3.3V, unless otherwise noted.)
CONDITIONS
PARAMETER
Supply-Voltage Range
Oscillator Supply Current
MIN
TYP
2.7
PREGND = unconnected
Prescaler Supply Current
(÷ 64/65 mode) (Note 1)
MAX
UNITS
4.8
V
9.5
14
mA
4.2
6
mA
Prescaler Supply Current
(buffer mode) (Note 2)
VDIV1 = 2.4V
5.4
8.5
mA
Receive Supply Current (Note 3)
VRXON = 2.4V, PREGND = unconnected
23
36
mA
Transmitter Supply Current (Note 4)
VRXON = 0.45V, VTXON = 2.4V,
PREGND = unconnected
20
32
mA
Shutdown Supply Current
VCOON = RXON = TXON TA = +25°C
= MOD = DIV1 = GND
TA = -40°C to +85°C
Digital Input Voltage High
RXON, TXON, DIV1, VCOON, MOD
Digital Input Voltage Low
RXON, TXON, DIV1, VCOON, MOD
Digital Input Current
Voltage on any one digital input = VCC or GND
0.5
10
2.4
µA
V
±1
0.45
V
±10
µA
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
(MAX2424/MAX2426 EV kit, VCC = +3.3V, fRXIN = 915MHz, PRXIN = -35dBm, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p,
fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
1000
MHz
RECEIVER (VRXON = 2.4V, fLO = 925.7MHz (MAX2424), fLO = 985MHz (MAX2426))
Input Frequency Range
IF Frequency Range
(Notes 5, 6)
800
MAX2424 (Notes 5, 6)
8.5
10.7
12.5
MAX2426 (Notes 5, 6)
55
70
85
Image Frequency Rejection
Conversion Power Gain
Noise Figure
Input Third-Order Intercept
(IIP3)
Input 1dB Compression
26
35
VLNAGAIN = VCC,
TA = +25°C (Note 7)
MAX2424
20
22
24.5
MAX2426
19
21
23.5
VLNAGAIN = VCC,
TA = -40°C to +85°C (Notes 5, 7)
MAX2424
19
25
MAX2426
18
24
VLNAGAIN = 1V (Note 7)
12
LNAGAIN = GND (Note 7)
-16
LNAGAIN = VCC (Notes 5, 7)
4
VLNAGAIN = 1V (Notes 5, 7)
12
LNAGAIN = VCC (Notes 5, 8)
-19
dB
5
-17
VLNAGAIN = 1V (Notes 5, 8)
-8
LNAGAIN = VCC
-26
VLNAGAIN = 1V
-18
MHz
dB
dB
dB
dBm
LO to RXIN Leakage
Receiver on or off
-60
dBm
Receiver Turn-On Time
(Note 9)
500
ns
TRANSMITTER (VTXON = 2.4V, fLO = 915MHz)
Output Frequency Range
(Notes 5, 10)
800
TA = +25°C
-9.5
TA = TMIN to TMAX (Note 5)
-10
Baseband 3dB Bandwidth
Output Power
125
Output 1dB Compression
Output Third-Order Intercept (OIP3)
1000
(Note 11)
-7
MHz
MHz
-5
-4.5
dBm
-0.5
dBm
3.5
dBm
Carrier Suppression
30
dBc
Output Noise Density
-140
dBm/Hz
220
ns
Transmitter Turn-On Time
(Note 12)
_______________________________________________________________________________________
3
MAX2424/MAX2426
AC ELECTRICAL CHARACTERISTICS
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2424/MAX2426 EV kit, VCC = +3.3V, fRXIN = 915MHz, PRXIN = -35dBm, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p,
fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
1100
MHz
OSCILLATOR AND PRESCALER
Oscillator Frequency Range
(Note 5)
Oscillator Phase Noise
10kHz offset (Note 13)
800
MAX2424
82
MAX2426
72
MAX2424
8
MAX2426
35
RX to TX with PRXIN =-45dBm (RX mode) MAX2424
to PRXIN = 0dBm (TX mode) (Note 14)
MAX2426
70
Standby to TX or Standby to RX
Oscillator Pulling
dBc/Hz
kHz
110
Prescaler Output Level
ZL = 100kΩ | | 10pF
Oscillator Buffer Output Level
(Notes 5, 13)
VDIV1 = 2.4V, ZL = 50Ω,
ZL = 50Ω
Required Modulus Setup Time
(Notes 5, 15)
÷ 64/65 mode
10
ns
Required Modulus Hold Time
(Notes 5, 15)
÷ 64/65 mode
0
ns
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
Note 15:
4
500
TA = +25°C
-11
TA = -40°C to +85°C
-12
-8
mVp-p
dBm
Guaranteed by design and characterization.
Image rejection typically falls to 30dBc at the frequency extremes.
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.
Two tones at PRXIN = -45dBm each, f1 = 915.0MHz and f2 = 915.2MHz.
Time delay from VRXON = 0.45V to VRXON = 2.4V transition to the time the output envelope reaches 90% of its final value.
Output power typically falls to -10dBm at the frequency extremes.
Two tones at VTXIN = 125mVp-p, f1 = 1.0MHz, and f2 = 1.2MHz.
Time delay from VTXON = 0.45V to VTXON = 2.4V transition to the time the output envelope reaches 90% of its final value.
Using tank components L3 = 5.0nH (Coilcraft A02T), C2 = C3 = C26 = 3.3pF, R6 = R7 = 10Ω.
This approximates a typical application in which TXOUT is followed by an external PA and a T/R switch with finite isolation.
Relative to the rising edge of PREOUT.
_______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
37
31
3.0
ICC (µA)
ICC (mA)
32
VCC = 3.3V
29
VCC = 2.7V
RXON = VCC
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
26
TXON = VCC
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
25
23
21
24
-20
20
40
60
80
VCC = 4.8V
-40
-20
0
20
40
60
VCC = 3.3V
1.0
0.5
VCC = 2.7V
0
-40
80
-20
0
20
40
60
TEMPERATURE (°C)
TEMPERATURE (°C)
RECEIVER GAIN vs. LNAGAIN
RECEIVER INPUT IP3 vs. LNAGAIN
RECEIVER NOISE FIGURE
vs. LNAGAIN
5
LNA
OFF
0
15
LNA
ADJUSTABLE MAX
PARTIALLY
GAIN
GAIN
BIASED
5
ADJUSTABLE
GAIN
0
IIP3 (dBm)
10
MAX
GAIN
-10
-5
AVOID
THIS
REGION
-10
-15
25
20
15
10
0
-20
1.0
1.5
2.0
0
0.5
1.0
RXON = VCC
DIV1 = VCC
AVOID
THIS
REGION
5
RXON = VCC
-20
0.5
LNA
ADJUSTABLE MAX
PARTIALLY
GAIN
GAIN
BIASED
-15
RXON = VCC
0
LNA
OFF
30
AVOID
THIS
REGION
-5
1.5
0
2.0
0.5
1.0
1.5
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
22
VCC = 3.3V
20
VCC = 2.7V
MAX2424/6-09
MAX2424/6-08
VCC = 4.8V
2.0
-6
VLNAGAIN = 1V
-8
-10
4.5
VCC = 3.3V
4.0
VCC = 2.7V
IIP3 (dBm)
VCC = 4.8V
LNAGAIN = VCC
RXON = VCC
DIV1 = VCC
5.0
NOISE FIGURE (dB)
24
5.5
MAX2424/6-07
LNAGAIN = VCC
RXON = VCC
80
40
35
NOISE FIGURE (dB)
LNA
PARTIALLY
BIASED
MAX2424/6-05
LNA
OFF
26
2.0
TEMPERATURE (°C)
25
20
0
MAX2424/6-04
-40
2.5
1.5
27
28
RECEIVER GAIN (dB)
VCC = 4.8V
33
34
30
RECEIVER GAIN (dB)
3.5
35
VCC = 2.7V
36
VCOON = GND
4.0
MAX2424/6-06
VCC = 3.3V
4.5
MAX2424/6-02
VCC = 4.8V
38
ICC (mA)
39
MAX2424/6-01
42
40
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
TRANSMITTER SUPPLY CURRENT
vs. TEMPERATURE
MAX2424/6-03
RECEIVER SUPPLY CURRENT
vs. TEMPERATURE
-12
-14
-16
VLNAGAIN = 2V
3.5
-18
18
RXON = VCC
3.0
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
-20
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX2424/MAX2426
__________________________________________Typical Operating Characteristics
(MAX2424/MAX2426 EV kit, VCC = +3.3V; fLO(RX) = 925.7MHz (MAX2424), 985MHz (MAX2426); fRXIN = 915MHz, PRXIN =
-35dBm, fLO(TX) = 915MHz, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V,
RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.)
______________________________Typical Operating Characteristics (continued)
(MAX2424/MAX2426 EV kit, VCC = +3.3V; fLO(RX) = 925.7MHz (MAX2424), 985MHz (MAX2426); fRXIN = 915MHz, PRXIN =
-35dBm, fLO(TX) = 915MHz, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V,
RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.)
50
VCC = 2.7V
-6
VCC = 3.3V
-7
-8
40
30
20
10
MAX2424
35
IMAGE REJECTION (dB)
-5
40
MAX2424/6-11
1dB COMPRESSION POINT (dBm)
RXON = VCC
IMAGE REJECTION (dB)
VCC = 4.8V
-4
RECEIVER IMAGE REJECTION
vs. IF FREQUENCY
60
MAX2424/6-10
-3
RECEIVER IMAGE REJECTION
vs. RF FREQUENCY
MAX2426
30
25
20
15
0
10
-10
5
-20
0
RXON = VCC
20
40
60
0
80
400
800
TEMPERATURE (°C)
RXIN INPUT IMPEDANCE
vs. FREQUENCY
45
40
-80
35
IMAGINARY
30
25
-60
REAL
20
-40
15
10
5
-100
1600
2000
TXON = VCC
VCC = 4.8V
VCC = 3.3V
-10
-15
0
-25
5
800
1000
1200
1400
FREQUENCY (MHz)
TXOUT OUTPUT IMPEDANCE
vs. FREQUENCY
100
REAL
IMAGINARY
-100
-150
-200
TXON = VCC
600 800 1000 1200 1400 1600 1800 2000
FREQUENCY (MHz)
VCC = 2.7V
VCC = 3.3V
TXON = VCC
-40
-20
0
20
40
60
80
TRANSMITTER 1dB COMPRESSION POINT
vs. TEMPERATURE
LO
-40
-50
-60
-80
-250
VCC = 4.8V
TEMPERATURE (°C)
-70
-300
6
1000
DOUBLE-SIDE
BAND
FUNDAMENTAL
TXON = VCC
-20
-30
0
-50
100
INPUT VOLTAGE (mVp-p)
0
-10
POWER (dBm)
50
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
-13
TRANSMITTER OUTPUT SPECTRUM
MAX2424/6-16
REAL OR IMAGINARY IMPEDANCE (Ω)
150
1000
-14
10
1
OUTPUT 1dB COMPRESSION (dBm)
600
MAX2424/6-17
0
100
TRANSMITTER OUTPUT POWER
vs. TEMPERATURE
VCC = 2.7V
-20
10
TRANSMITTER OUTPUT POWER
vs. INPUT VOLTAGE
-5
-20
1
IF FREQUENCY (MHz)
0
OUTPUT POWER (dBm)
RXON = VCC
IMAGINARY IMPEDANCE (Ω)
MAX2424/6-13
50
1200
RF FREQUENCY (MHz)
MAX2424/6-15
0
RXON = VCC
MAX2424/6-18
-20
OUTPUT POWER (dBm)
-40
MAX2424/6-14
-9
MAX2424/6-12
MAX2424
RECEIVER OUTPUT 1dB
COMPRESSION POINT vs. TEMPERATURE
REAL IMPEDANCE (Ω)
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
VCC = 4.8V
0
-1
-2
VCC = 3.3V
-3
-4
VCC = 2.7V
-5
-6
-90
-100
-7
910 911 912 913 914 915 916 917 918 919 920
FREQUENCY (MHz)
TXON = VCC
-40
-20
0
20
40
TEMPERATURE (°C)
_______________________________________________________________________________________
60
80
900MHz Image-Reject Receiver
with Transmit Mixer
TRANSMITTER BASEBAND
FREQUENCY RESPONSE
TXON = VCC
NOTE: TXIN IS TOTAL
VOLTAGE FOR TWO TONES
(PEAK-TO-PEAK)
0
-10
-30
-40
TXOUT (dBc)
POWER (dBm)
-20
FUNDAMENTAL
-50
-60
IM3 LEVEL
-70
-80
-90
-100
10
100
1000
3
0
-3
-6
-9
-12
-15
-18
-21
-24
-27
-30
-33
-36
MAX2424/6-20
10
MAX2424/6-19
POWER vs. TXIN VOLTAGE
TXON = VCC
1
10
100
1000
FREQUENCY (MHz)
TXIN VOLTAGE (mVp-p)
______________________________________________________________Pin Description
PIN
NAME
FUNCTION
1
VCC
2
CAP1
3
RXOUT
4
GND
Ground Connection
5
RXIN
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
VCC
Supply Voltage Input for the Receive Low-Noise Amplifier. Bypass with a 47pF low-inductance capacitor
to GND (pin 7 recommended).
7
GND
Ground Connection for Receive Low-Noise Amplifier. Connect directly to ground plane using multiple
vias.
8
GND
Ground Connection for Signal-Path Blocks, except LNA
9
TXOUT
Supply-Voltage Input for Master Bias Cell. Bypass with a 47pF low-inductance capacitor and 0.1µF to
GND (pin 28 recommended).
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.
Single-ended, 330Ω IF Output. AC couple to this pin.
PA Predriver Output. See Figure 1 for an example matching network, which provides better than 2:1
VSWR from 902MHz to 928MHz.
10
LNAGAIN
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.
11
VCC
Supply Voltage Input for the Signal-Path Blocks, except LNA. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND (pin 8 recommended).
_______________________________________________________________________________________
7
MAX2424/MAX2426
______________________________Typical Operating Characteristics (continued)
(MAX2424/MAX2426 EV kit, VCC = +3.3V; fLO(RX) = 925.7MHz (MAX2424), 985MHz (MAX2426); fRXIN = 915MHz, PRXIN =
-35dBm, fLO(TX) = 915MHz, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V,
RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.)
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
_________________________________________________Pin Description (continued)
8
PIN
NAME
FUNCTION
12
TXIN
Transmit Mixer’s Noninverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input
port. See Figure 1.
13
TXIN
Transmit Mixer’s Inverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port.
See Figure 1.
14
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.
15
TXON
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.
16
RXON
Drive RXON and VCOON with a logic high to enable the LNA, receive mixer, and IF output buffer.
See Power Management section.
17
VCOON
Drive VCOON with a logic high to turn on the VCO, phase shifters, VCO buffers, and prescaler. To disable the prescaler, leave the PREGND pin unconnected.
18
DIV1
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 divideby-64/65 operation. Drive this pin low when in shutdown to minimize shutdown current.
19
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.
20
PREGND
Ground connection for the Prescaler. Connect PREGND to ground for normal operation. Leave unconnected to disable the prescaler and the output buffer. Connect MOD and DIV1 to ground and leave PREOUT unconnected when disabling the prescaler.
21
PREOUT
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.
22
VCC
Supply-Voltage Input for Prescaler. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND
(pin 20 recommended).
23
VCC
Supply-Voltage Input for VCO and Phase Shifters. Bypass with a 47pF low-inductance capacitor to GND
(pin 26 recommended).
24
TANK
Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using
an external oscillator.
25
TANK
Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using
an external oscillator.
26
GND
Ground Connection for VCO and Phase Shifters
27
GND
Ground (substrate)
28
GND
Ground Connection for Master Bias Cell
_______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
VCC
1
0.1µF
VCC
VCC
22
47pF
47pF
28
GND
PREGND
0.01µF
20
VCO TANK COMPONENTS
FOR 915MHz RF FREQUENCY
VCC
2
0.1µF
CAP1
VCC
23
DEVICE
L3
(nH)
C2, C3
(pF)
C26
(pF)
R6, R7
(Ω)
26
MAX2424
6.8
3.3
2.0
10
27
MAX2426
3.3
8.0
4.0
20
47pF
47pF
GND
RECEIVE
RF INPUT
MAX2424/MAX2426
VCC
8.2nH
5
RXIN
47pF
MAX2424
MAX2426
GND
0.01µF
RXOUT
3
RECEIVE IF OUTPUT (330Ω)
VCC
12nH
0.01µF*
47pF
MODULATOR INPUT
22nH
TXIN
47pF
9
18nH
TRANSMIT
RF OUTPUT
12
10k
TXOUT
RA
TXIN
RB
VCC
10k
13
MODULATOR INPUT
0.01µF*
VCC
6
47pF
7
100nH
GND
VCC
11
0.01µF
VARACTORS:
ALPHA SMV1299-004
OR EQUIVALENT
1k
VCC
VCC
TANK
25
R7
C2
47k
47pF
C26
L3
8
GND
TANK
24
R6
1000pF
14
0.01µF
CAP2
PREOUT
47pF
MOD
DIV1
VCOON
10
LNAGAIN
LNAGAIN
RXON
GND
TXON
21
19
18
17
16
C3
15
1k
TO PLL
MOD
DIV1
VCOON
RXON
47pF
4
VCO
ADJUST
47pF
TXON
* WHEN USING DIFFERENTIAL
SOURCE, REMOVE RESISTORS
AND REPLACE CAPACITORS WITH
SHORTS. FOR SINGLE-ENDED
SOURCE, DRIVE ONLY MODULATOR
INPUT. CHOOSE RA AND RB VALUES
AS SHOWN IN TRANSMITTER SECTION.
Figure 1. Typical Operating Circuit
_______________________________________________________________________________________
9
MAX2424/MAX2426
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
The MAX2424/MAX2426’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 provides optimum
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
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 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 for LNAGAIN voltages above 1V. See the receiver gain, IP3, and
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.
A quadrature LO drives the local-oscillator (LO) port of
Table 1. LNA Modes
LNAGAIN
VOLTAGE (V)
0 < VLNAGAIN ≤ 0.5
MODE
LNA capacitively bypassed,
minimum gain, maximum IP3
0.5 < VLNAGAIN < 1.0
LNA partially biased. Avoid this
mode— the LNA operates in a
Class C manner
1.0 < VLNAGAIN ≤ 1.5
LNA gain is monotonically
adjustable
1.5 < VLNAGAIN ≤ VCC
LNA at maximum gain
(remains monotonic)
10
TXIN
1.5µA
2M
VMIXER INPUT
TXIN
1.5µA
Figure 2. TXIN, TXIN Equivalent Circuit
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 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.
Transmitter
The MAX2424/MAX2426 transmitter consists of a balanced mixer and a PA driver amplifier. The mixer inputs
are accessible via the TXIN and TXIN pins. An equivalent 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 multiply 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.
Set the common-mode voltage at TXIN, TXIN to 2.3V by
selecting appropriate values for RA and RB (Figure 1). The
total series impedance of RA and RB should be approximately 100kΩ.
Frequency modulation (FM) is realized by modulating
the VCO tuning voltage. Apply the appropriate differential and common-mode voltages to TXIN and TXIN to
control transmitter output power (Figure 3).
______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
R1
The MAX2424/MAX2426 uses passive networks to provide quadrature phase shifting for the receive IF and LO
signals. Because these networks are frequency selective, 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).
MAX2424
MAX2426
i
1.5µA
TXIN
2M
R2
TXIN
Local Oscillator (LO)
1.5µA
R3
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 for an example VCO
tank circuit.
RT = R1 + R2 + R3
VDIFF = VTXIN - V TXIN
Figure 3. Biasing TXIN and TXIN for FM
For example, if VCC = 3.3V and POUT = -8dBm, choose
RT = 100kΩ for sufficient current through the divider, so
that bias currents for TXIN and TXIN have little effect
over temperature. Set VTXIN = 2.3V to satisfy commonmode voltage range requirements at VCC = 3.3V.
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
VDIFF. A -8dBm transmitter output requires 250mVp-p /
2√2 = 88.4mV.
VTXIN = 2.3V + 0.0884V = 2.3884V
RT = R1 + R2 + R3
Solve for resistors R1, R2, and R3 with the following
equations:
R3 =
V TXIN x RT
(
VCC
R2 = VTXIN – V TXIN
) x VR
T
CC
R1 = RT – R2 – R3
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.
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 V CC. See the
Applications Information section for details.
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.
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.
In divide-by-64/65 drive mode, the division ratio is controlled 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
MAX2424/MAX2426
Phase Shifter
VCC
MAX2424/MAX2426
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.
Power Management
The MAX2424/MAX2426 supports four different powermanagement 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 upconverter mixer and PA predriver. VCOON must be high for
the transmitter to operate. When TXON is low, the transmitter is off.
To disable all chip functions and reduce the supply current to typically 0.5µA, pull VCOON, DIV1, MOD, RXON,
and TXON low.
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 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.
VCC
___________Applications Information
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 capacitors C2, C3, and both halves of the varactor diode
capacitance set the resonant frequency as follows:
fr =
CEFF =
1
( )(
MAX2424
MAX2426
TANK
)
1
+ C26
 1
1
2 
 C2 + C3 + C 

D1 
R7
C2
R5
1k
1/2 D1
L3
6.8nH
R6
TANK


2π L3 CEFF 
L4
100nH
VCO_CTRL
C26
C3
1/2 D1
C1
47pF
R4
1k
D1 = ALPHA SMV1299-004
SEE FIGURE 1 FOR R6, R7, C2, C3, C26, AND L3 COMPONENT VALUES.
Figure 4. Oscillator Tank Schematic Using the On-Chip VCO
where CD1 is the capacitance of one varactor diode.
12
R8
47k
______________________________________________________________________________________
900MHz Image-Reject Receiver
with Transmit Mixer
TANK
L3
L1
MAX2424/MAX2426
LT
MAX2424
MAX2426
R1
1/2 D1
L4
R2
VTUNE
Ci
C2
VCC
C1
1/2 D1
L2
LT
R3
L5
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
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 0 and 50Ω. Proper
high frequency bypassing (C1) should be used for the
bias voltage to eliminate power supply noise from
entering the tank.
Oscillator Tank PC Board Layout
The parasitic PC board capacitance, as well as PCB
trace inductance and package inductance, 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
reduces parasitic capacitance.
VCC
MAX2424
50Ω
47pF
TANK
VCC
50Ω
50Ω
EXT LO
TANK
50Ω
EXTERNAL LO LEVEL IS 0dBm
FROM A 50Ω SOURCE.
47pF
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 VCC supply via 50Ω resistors.
If a differential LO source such as the MAX2620 is
available, AC-couple the inverting output into TANK.
______________________________________________________________________________________
13
_________________________________________________________Functional Diagram
LNAGAIN
90°
Σ
RXIN
RXOUT
0°
DIV1
MOD
CAP1
RXON
TXON
CAP2
0°
90°
÷ 1/64/65
BIAS
PREOUT
PREGND
TANK
PHASE
SHIFTER
TANK
VCOON
0°
TXOUT
MAX2424
MAX2426
TXIN
TXIN
________________________________________________________Package Information
SSOP.EPS
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
14
______________________________________________________________________________________