Maxim MAX24276EAI, MAX2424EAI Datasheet

________________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.
________________________Applications
Cordless Phones
Wireless Telemetry
Wireless Networks
Spread-Spectrum Communications
Two-Way Paging
____________________________Features
Receive Mixer with 35dB Image RejectionAdjustable-Gain LNAUp to +2dBm Combined Receiver Input IP34dB Combined Receiver Noise FigureOptimized for Common Receiver IF Frequencies:
10.7MHz (MAX2424) 70MHz (MAX2426)
PA Predriver Provides up to 0dBmLow Current Consumption: 23mA Receive
20mA Transmit
9.5mA Oscillator
0.5µA Shutdown ModeOperates from Single +2.7V to +4.8V Supply
MAX2424/MAX2426
900MHz Image-Reject Receivers
with Transmit Mixer
________________________________________________________________
Maxim Integrated Products
1
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
GND
GND
GND
TANK
TXON
PREOUT
PREGND
MOD
DIV1
VCOON
RXON
CAP2
TXIN
TXIN
LNAGAIN
TXOUT
GND
GND
RXIN
GND
RXOUT
CAP1
SSOP
TOP VIEW
MAX2424 MAX2426
TANK
V
CC
V
CC
V
CC
V
CC
V
CC
___________________Pin Configuration
19-1350 Rev 2; 2/99
PART
MAX2424EAI
-40°C to +85°C
TEMP. RANGE PIN-PACKAGE
28 SSOP
_______________Ordering Information
Functional Diagram appears at end of data sheet.
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
MAX2426EAI
-40°C to +85°C 28 SSOP
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.
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(VCC= +2.7V to +4.8V, no RF signals applied, LNAGAIN = Unconnected, V
TXIN
= V
TXIN
= 2.3V, V
VCOON
= 2.4V, V
RXON
= V
TXON
=
V
MOD
= V
DIV1
= 0.45V, PREGND = GND, TA= -40°C to +85°C. Typicals are at TA= +25°C, VCC= 3.3V, unless otherwise noted.)
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: 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.
V
CC
to GND...........................................................-0.3V to +5.5V
TXIN, TXIN Differential Voltage..............................................+2V
Voltage on TXOUT......................................-0.3V to (V
CC
+ 1.0V)
Voltage on LNAGAIN, TXON, RXON, VCOON,
DIV1, MOD, TXIN, TXIN............................-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 ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +165°C
Lead Temperature (soldering, 10sec) .............................+300°C
PARAMETER
MIN TYP MAX UNITS
Receive Supply Current (Note 3) 23 36 mA
Prescaler Supply Current (buffer mode) (Note 2)
5.4 8.5 mA
Oscillator Supply Current
Supply-Voltage Range 2.7 4.8 V
9.5 14 mA
Prescaler Supply Current (÷ 64/65 mode) (Note 1)
4.2 6 mA
CONDITIONS
V
RXON
= 2.4V, PREGND = unconnected
V
DIV1
= 2.4V
PREGND = unconnected
Digital Input Voltage Low 0.45 V
Shutdown Supply Current
0.5
RXON, TXON, DIV1, VCOON, MOD
VCOON = RXON = TXON = MOD = DIV1 = GND
Digital Input Current ±1 ±10 µAVoltage on any one digital input = VCCor GND
Digital Input Voltage High V2.4RXON, TXON, DIV1, VCOON, MOD
10
µA
TA= +25°C TA= -40°C to +85°C
Transmitter Supply Current (Note 4) 20 32 mA
V
RXON
= 0.45V, V
TXON
= 2.4V,
PREGND = unconnected
AC ELECTRICAL CHARACTERISTICS
(MAX2424/MAX2426 EV kit, VCC= +3.3V, f
RXIN
= 915MHz, P
RXIN
= -35dBm, V
TXIN
= V
TXIN
= 2.3V (DC bias), V
TXIN
= 250mVp-p,
f
TXIN
= 1MHz, V
LNAGAIN
= 2V, V
VCOON
= 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
_______________________________________________________________________________________ 3
(Note 11)
MAX2424 (Notes 5, 6)
TA= T
MIN
to T
MAX
(Note 5)
TA= +25°C
(Notes 5, 6)
(Notes 5, 10)
(Note 9)
Receiver on or off
LNAGAIN = GND (Note 7)
V
LNAGAIN
= 1V (Note 7)
V
LNAGAIN
= 1V (Notes 5, 8)
LNAGAIN = V
CC
(Notes 5, 8)
V
LNAGAIN
= VCC,
TA= -40°C to +85°C (Notes 5, 7)
MAX2426 (Notes 5, 6)
V
LNAGAIN
= VCC,
TA= +25°C (Note 7)
V
LNAGAIN
= 1V (Notes 5, 7)
LNAGAIN = V
CC
(Notes 5, 7)
CONDITIONS
dBc30Carrier Suppression
dBm3.5Output Third-Order Intercept (OIP3)
dBm-0.5Output 1dB Compression
-10 -4.5
dBm
-9.5 -7 -5
Output Power
MHz125Baseband 3dB Bandwidth
MHz800 1000Output Frequency Range
ns500Receiver Turn-On Time
dBm-60LO to RXIN Leakage
-8
dB
-19 -17
Input Third-Order Intercept (IIP3)
12
dB
45
Noise Figure
MHz
8.5 10.7 12.5
MHz800 1000Input Frequency Range
-16
12
18 24
19 25
55 70 85
IF Frequency Range
dB26 35Image Frequency Rejection
dB
20 22 24.5
Conversion Power Gain
19 21 23.5
UNITSMIN TYP MAXPARAMETER
MAX2424 MAX2426 MAX2424 MAX2426
V
LNAGAIN
= 1V
LNAGAIN = V
CC
-18
dBm
-26
Input 1dB Compression
(Note 12) ns220Transmitter Turn-On Time
dBm/Hz-140Output Noise Density
RECEIVER (V
RXON
= 2.4V, fLO= 925.7MHz (MAX2424), fLO= 985MHz (MAX2426))
TRANSMITTER (V
TXON
= 2.4V, fLO= 915MHz)
V
DIV1
= 2.4V, ZL= 50,
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
4 _______________________________________________________________________________________
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2424/MAX2426 EV kit, VCC= +3.3V, f
RXIN
= 915MHz, P
RXIN
= -35dBm, V
TXIN
= V
TXIN
= 2.3V (DC bias), V
TXIN
= 250mVp-p,
f
TXIN
= 1MHz, V
LNAGAIN
= 2V, V
VCOON
= 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)
PARAMETER MIN TYP MAX UNITS
Oscillator Phase Noise
Oscillator Frequency Range 800 1100 MHz
82
dBc/Hz
(Note 5)
CONDITIONS
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
RXIN
= -45dBm each, f1 = 915.0MHz and f2 = 915.2MHz.
Note 9: Time delay from V
RXON
= 0.45V to V
RXON
= 2.4V transition to the time the output envelope reaches 90% of its final value.
Note 10: Output power typically falls to -10dBm at the frequency extremes. Note 11: Two tones at V
TXIN
= 125mVp-p, f1 = 1.0MHz, and f2 = 1.2MHz.
Note 12: Time delay from V
TXON
= 0.45V to V
TXON
= 2.4V transition to the time the output envelope reaches 90% of its final value.
Note 13: Using tank components L3 = 5.0nH (Coilcraft A02T), C2 = C3 = C26 = 3.3pF, R6 = R7 = 10. 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.
Prescaler Output Level
500 mVp-p
-11 -8
Required Modulus Setup Time (Notes 5, 15)
10 ns
ZL= 100k
| |
10pF
÷ 64/65 mode
Required Modulus Hold Time (Notes 5, 15)
0 ns
÷ 64/65 mode
Oscillator Buffer Output Level (Notes 5, 13)
-12
dBm
V
DIV1
= 2.4V,
ZL= 50
10kHz offset (Note 13)
72
Standby to TX or Standby to RX
35
Oscillator Pulling
8
kHz
110
RX to TX with P
RXIN
=-45dBm (RX mode)
to P
RXIN
= 0dBm (TX mode) (Note 14)
MAX2424 MAX2426 MAX2424 MAX2426 MAX2424 MAX2426
70
TA= +25°C TA= -40°C to +85°C
OSCILLATOR AND PRESCALER
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
_______________________________________________________________________________________
5
28
32
30
38
36
34
42
40
24
26
-40 0 20-20 40 60 80
RECEIVER SUPPLY CURRENT
vs. TEMPERATURE
MAX2424/6-01
TEMPERATURE (°C)
I
CC
(mA)
VCC = 2.7V
VCC = 3.3V
VCC = 4.8V
RXON = V
CC
PREGND = UNCONNECTED INCLUDES OSCILLATOR CURRENT
37
35
33
31
29
27
25
23
21
39
-40 0 20-20 40 60 80
TRANSMITTER SUPPLY CURRENT
vs. TEMPERATURE
MAX2424/6-02
TEMPERATURE (°C)
I
CC
(mA)
VCC = 2.7V
VCC = 3.3V
VCC = 4.8V
TXON = V
CC
PREGND = UNCONNECTED INCLUDES OSCILLATOR CURRENT
0
1.0
0.5
2.5
2.0
1.5
4.0
3.5
3.0
4.5
-40 0 20-20 40 60 80
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX2424/6-03
TEMPERATURE (°C)
I
CC
(µA)
VCC = 2.7V
VCC = 3.3V
VCC = 4.8V
VCOON = GND
25
20
15
10
5
0
-5
-10
-15
-20 0 0.5 1.0 1.5 2.0
RECEIVER GAIN vs. LNAGAIN
MAX2424/6-04
LNAGAIN VOLTAGE (V)
RECEIVER GAIN (dB)
ADJUSTABLE
GAIN
MAX GAIN
LNA
PARTIALLY
BIASED
LNA OFF
AVOID
THIS
REGION
RXON = V
CC
18
22
20
26
24
-40 0 20-20 40 60 80
MAX2424
RECEIVER GAIN vs. TEMPERATURE
MAX2424/6-07
TEMPERATURE (°C)
RECEIVER GAIN (dB)
VCC = 2.7V
VCC = 3.3V
VCC = 4.8V
LNAGAIN = V
CC
RXON = V
CC
-20
-15
-10
-5
0
5
0 0.5 1.0 1.5 2.0
RECEIVER INPUT IP3 vs. LNAGAIN
MAX2424/6-05
LNAGAIN VOLTAGE (V)
IIP3 (dBm)
ADJUSTABLE
GAIN
AVOID
THIS
REGION
MAX GAIN
LNA
PARTIALLY
BIASED
LNA OFF
RXON = V
CC
0
5
15
10
25
20
30
40
35
0 0.5 1.0 1.5 2.0
RECEIVER NOISE FIGURE
vs. LNAGAIN
MAX2424/6-06
LNAGAIN VOLTAGE (V)
NOISE FIGURE (dB)
ADJUSTABLE
GAIN
AVOID
THIS
REGION
MAX
GAIN
LNA
PARTIALLY
BIASED
LNA OFF
RXON = V
CC
DIV1 = V
CC
3.0
4.0
3.5
5.0
5.5
4.5
-40 0 20-20 40 60 80
RECEIVER NOISE FIGURE vs.
TEMPERATURE AND SUPPLY VOLTAGE
MAX2424/6-08
TEMPERATURE (°C)
NOISE FIGURE (dB)
VCC = 3.3V
LNAGAIN = V
CC
RXON = V
CC
DIV1 = V
CC
VCC = 4.8V
V
CC
= 2.7V
-20
-16
-18
-8
-10
-6
-12
-14
-40 0 20-20 40 60 80
RECEIVER INPUT IP3
vs. TEMPERATURE
MAX2424/6-09
TEMPERATURE (°C)
IIP3 (dBm)
V
LNAGAIN
= 1V
RXON = V
CC
V
LNAGAIN
= 2V
__________________________________________Typical Operating Characteristics
(MAX2424/MAX2426 EV kit, VCC= +3.3V; f
LO(
RX)
= 925.7MHz (MAX2424), 985MHz (MAX2426); f
RXIN
= 915MHz, P
RXIN
=
-35dBm, f
LO(TX)
= 915MHz, V
TXIN
= V
TXIN
= 2.3V (DC bias), V
TXIN
= 250mVp-p, f
TXIN
= 1MHz, V
LNAGAIN
= 2V, V
VCOON
= 2.4V,
RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
6 _______________________________________________________________________________________
______________________________Typical Operating Characteristics (continued)
(MAX2424/MAX2426 EV kit, VCC= +3.3V; f
LO(
RX)
= 925.7MHz (MAX2424), 985MHz (MAX2426); f
RXIN
= 915MHz, P
RXIN
=
-35dBm, f
LO(TX)
= 915MHz, V
TXIN
= V
TXIN
= 2.3V (DC bias), V
TXIN
= 250mVp-p, f
TXIN
= 1MHz, V
LNAGAIN
= 2V, V
VCOON
= 2.4V,
RXON = TXON = 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
MAX2424/6-11
RF FREQUENCY (MHz)
IMAGE REJECTION (dB)
RXON = V
CC
-9
-8
-4
-5
-3
-6
-7
-40 0 20-20 40 60 80
MAX2424
RECEIVER OUTPUT 1dB
COMPRESSION POINT vs. TEMPERATURE
MAX2424/6-10
TEMPERATURE (°C)
1dB COMPRESSION POINT (dBm)
VCC = 2.7V
VCC = 4.8V
RXON = V
CC
VCC = 3.3V
0
10
20
30
5
15
25
35
40
1 10 100 1000
RECEIVER IMAGE REJECTION
vs. IF FREQUENCY
MAX2424/6-12
IF FREQUENCY (MHz)
IMAGE REJECTION (dB)
RXON = V
CC
MAX2424 MAX2426
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
MAX2424/6-13
FREQUENCY (MHz)
REAL IMPEDANCE ()
IMAGINARY IMPEDANCE ()
REAL
IMAGINARY
RXON = V
CC
-300
-200
-250
-50
-100
-150
0
50
100
150
800600 1000 1200 1400 1600 1800 2000
TXOUT OUTPUT IMPEDANCE
vs. FREQUENCY
MAX2424/6-16
FREQUENCY (MHz)
REAL OR IMAGINARY IMPEDANCE ()
REAL
IMAGINARY
TXON = V
CC
5
-25
-15
-20
-5
-10
0
TRANSMITTER OUTPUT POWER
vs. INPUT VOLTAGE
MAX2424/6-14
INPUT VOLTAGE (mVp-p)
OUTPUT POWER (dBm)
10 100 1000
VCC = 2.7V
V
CC
= 4.8V
V
CC
= 3.3V
TXON = V
CC
-14
-2
-3
-4
-5
-6
-7
-8
-9
-10
-11
-12
-13
-40 0
20
-20
40 60 80
TRANSMITTER OUTPUT POWER
vs. TEMPERATURE
MAX2424/6-15
TEMPERATURE (°C)
OUTPUT POWER (dBm)
VCC = 2.7V
VCC = 4.8V
VCC = 3.3V
TXON = V
CC
-100
-80
-90
-60
-70
-40
-50
-30
-10
-20
0
910 912 913 914911 915 916 917 919918 920
TRANSMITTER OUTPUT SPECTRUM
MAX2424/6-17
FREQUENCY (MHz)
POWER (dBm)
DOUBLE-SIDE BAND FUNDAMENTAL
LO
TXON = V
CC
-7
-5
-6
-3
-4
0
-1
-2
1
-40 0-20 20 40 60 80
TRANSMITTER 1dB COMPRESSION POINT
vs. TEMPERATURE
MAX2424/6-18
TEMPERATURE (°C)
OUTPUT 1dB COMPRESSION (dBm)
VCC = 4.8V
VCC = 3.3V
VCC = 2.7V
TXON = V
CC
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
_______________________________________________________________________________________
7
-36
3 0
-3
-6
-9
-12
-15
-18
-21
-24
-27
-30
-33
1 10 100 1000
TRANSMITTER BASEBAND
FREQUENCY RESPONSE
MAX2424/6-20
FREQUENCY (MHz)
TXOUT (dBc)
TXON = V
CC
-100
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
10 100 1000
POWER vs. TXIN VOLTAGE
MAX2424/6-19
TXIN VOLTAGE (mVp-p)
POWER (dBm)
TXON = V
CC
NOTE: TXIN IS TOTAL VOLTAGE FOR TWO TONES (PEAK-TO-PEAK)
FUNDAMENTAL
IM3 LEVEL
______________________________Typical Operating Characteristics (continued)
(MAX2424/MAX2426 EV kit, VCC= +3.3V; f
LO(
RX)
= 925.7MHz (MAX2424), 985MHz (MAX2426); f
RXIN
= 915MHz, P
RXIN
=
-35dBm, f
LO(TX)
= 915MHz, V
TXIN
= V
TXIN
= 2.3V (DC bias), V
TXIN
= 250mVp-p, f
TXIN
= 1MHz, V
LNAGAIN
= 2V, V
VCOON
= 2.4V,
RXON = TXON = MOD = DIV1 = PREGND = GND, TA= +25°C, unless otherwise noted.)
______________________________________________________________Pin Description
Supply Voltage Input for the Receive Low-Noise Amplifier. Bypass with a 47pF low-inductance capacitor to GND (pin 7 recommended).
6
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
Ground Connection4
V
CC
RXIN
GND
Single-ended, 330IF Output. AC couple to this pin. 3
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
Supply-Voltage Input for Master Bias Cell. Bypass with a 47pF low-inductance capacitor and 0.1µF to GND (pin 28 recommended).
1
FUNCTIONPIN
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
PA Predriver Output. See Figure 1 for an example matching network, which provides better than 2:1 VSWR from 902MHz to 928MHz.
9
LNAGAIN
TXOUT
Ground Connection for Receive Low-Noise Amplifier. Connect directly to ground plane using multiple vias.
7 GND
RXOUT
CAP1
V
CC
NAME
Ground Connection for Signal-Path Blocks, except LNA8 GND
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).
11 V
CC
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
8 _______________________________________________________________________________________
_________________________________________________Pin Description (continued)
FUNCTIONPIN NAME
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.
14
Transmit Mixer’s Inverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port. See Figure 1.
13
CAP2
TXIN
Transmit Mixer’s Noninverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port. See Figure 1.
12 TXIN
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 50 load. AC couple to this pin.
21
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.
20
PREOUT
PREGND
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.
19
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.
17
Drive RXON and VCOON with a logic high to enable the LNA, receive mixer, and IF output buffer. See
Power Management
section.
16
MOD
VCOON
RXON
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.
15 TXON
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 50load. Drive DIV1 low for divide­by-64/65 operation. Drive this pin low when in shutdown to minimize shutdown current.
18 DIV1
Supply-Voltage Input for Prescaler. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND (pin 20 recommended).
22 V
CC
Differential Oscillator Tank Port. See
Applications Information
for information on tank circuits or on using
an external oscillator.
24
TANK
Supply-Voltage Input for VCO and Phase Shifters. Bypass with a 47pF low-inductance capacitor to GND (pin 26 recommended).
23 V
CC
Differential Oscillator Tank Port. See
Applications Information
for information on tank circuits or on using
an external oscillator.
25 TANK
Ground Connection for VCO and Phase Shifters26 GND
Ground (substrate)27 GND
Ground Connection for Master Bias Cell28 GND
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
_______________________________________________________________________________________ 9
V
CC
V
CC
17
16
15
18
19
21
1000pF
VARACTORS: ALPHA SMV1299-004 OR EQUIVALENT
WHEN USING DIFFERENTIAL SOURCE, REMOVE RESISTORS AND REPLACE CAPACITORS WITH SHORTS. FOR SINGLE-ENDED SOURCE, DRIVE ONLY MODULATOR INPUT. CHOOSE R
A
AND RB VALUES
AS SHOWN IN
TRANSMITTER
SECTION.
RECEIVE IF OUTPUT (330)
27
23
26
3
20
22
1
28
RECEIVE
RF INPUT
TRANSMIT
RF OUTPUT
5
9
7
6
0.01µF
47pF
V
CCVCC
0.1µF
V
CC
V
CC
V
CC
2
47pF
47pF
0.1µF
8.2nH
12nH
22nH
18nH
47pF
47pF
47pF
8
11
0.01µF
47pF
0.01µF
VCO TANK COMPONENTS
FOR 915MHz RF FREQUENCY
47pF
14
0.01µF
47pF
RXIN
TXOUT
GND
V
CC
V
CC
GND
GND
CAP2
GND
CAP1
V
CC
V
CC
TXON
RXON
VCOON
DIV1
MOD
PREOUT
TXON
RXON
VCOON
DIV1
MOD
TO PLL
GND
RXOUT
100nH
GND
PREGND
47pF
24
25
VCO ADJUST
C3
1k
47k
47pF
1k
C2
C26
R6
R7
V
CC
V
CC
R
A
R
B
10k
10k
L3
TANK
MODULATOR INPUT
12
0.01µF*
TXIN
MODULATOR INPUT
13
0.01µF*
TXIN
LNAGAIN
LNAGAIN
4
47pF
10
MAX2424 MAX2426
TANK
*
MAX2424
MAX2426
DEVICE
10
20
R6, R7
()
2.0
4.0
C26 (pF)
6.8
3.3
L3
(nH)
3.3
8.0
C2, C3
(pF)
Figure 1. Typical Operating Circuit
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
10 ______________________________________________________________________________________
_______________Detailed Description
The following sections describe each of the functional blocks shown in the
Functional Diagram.
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
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 330output.
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 RAand RB(Figure 1). The total series impedance of RAand RBshould 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).
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
LNAGAIN
V
CC
1.0 < V
LNAGAIN
1.5
0.5 < V
LNAGAIN
< 1.0
0 < V
LNAGAIN
0.5
LNAGAIN
VOLTAGE (V)
Table 1. LNA Modes
MAX2424 MAX2426
TXIN
2M
1.5µA
1.5µA
VMIXER INPUT
TXIN
Figure 2. TXIN, TXIN Equivalent Circuit
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
______________________________________________________________________________________ 11
For example, if VCC= 3.3V and P
OUT
= -8dBm, choose RT= 100kfor sufficient current through the divider, so that bias currents for TXIN and TXIN have little effect over temperature. Set V
TXIN
= 2.3V to satisfy common-
mode 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 22 and use it for V
DIFF
. A -8dBm transmitter output requires 250mVp-p /
22 = 88.4mV.
V
TXIN
= 2.3V + 0.0884V = 2.3884V
RT= R1 + R2 + R3
Solve for resistors R1, R2, and R3 with the following equations:
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.
Phase Shifter
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).
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 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 50, 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 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 50load. 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.
R3
V x R
V
R2 V – V x
R
V
R1 R – R2 – R3
T
CC
TXIN
T
CC
T
=
=
()
=
TXIN
TXIN
RT = R1 + R2 + R
3
V
DIFF
= V
TXIN
- V
TXIN
R1 i
R2
R3
2M
V
CC
1.5µA
TXIN
1.5µA
TXIN
MAX2424 MAX2426
Figure 3. Biasing TXIN and TXIN for FM
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.
___________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:
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 20to reduce the Q of parasitic resonance due to series package inductance L
T
. 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.
C =
1
1C21
C32C
EFF
D1
++
 
 
+ C26
f =
1
2L3C
r
EFF
π
()
()
 
 
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
12 ______________________________________________________________________________________
MAX2424 MAX2426
TANK
L3
6.8nH
L4
100nH
R5 1k
R4 1k
1/2 D1
1/2 D1
D1 = ALPHA SMV1299-004
SEE FIGURE 1 FOR R6, R7, C2, C3, C26, AND L3 COMPONENT VALUES.
C1 47pF
VCO_CTRL
R7
R6
C3
R8
47k
C2
C26
V
CC
TANK
Figure 4. Oscillator Tank Schematic Using the On-Chip VCO
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 50. 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.
Using an External Oscillator
If an external 50LO 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 50source. For proper biasing of the oscillator input stage, pull up the TANK and TANK pins to the VCCsupply via 50resistors.
If a differential LO source such as the MAX2620 is available, AC-couple the inverting output into TANK.
MAX2424/MAX2426
900MHz Image-Reject Receiver
with Transmit Mixer
______________________________________________________________________________________ 13
MAX2424
TANK
50
50
50
47pF
50
EXT LO
EXTERNAL LO LEVEL IS 0dBm FROM A 50SOURCE.
V
CC
47pF
V
CC
TANK
Figure 6. Using an External Local Oscillator
MAX2424 MAX2426
TANK
L1
L
T
L
T
L2
L3
L4
L5
R1
R2
R3
C
i
1/2 D1
1/2 D1
C1C2
V
CC
V
TUNE
TANK
Figure 5. Series-Coupled Resonant Tank for Wide Tuning Range and Low Phase Noise
MAX2424/MAX2426
900MHz Image-Reject Receiver with Transmit Mixer
14 ______________________________________________________________________________________
_________________________________________________________Functional Diagram
RXON TXON
CAP2
TXOUT
CAP1
RXIN
LNAGAIN
90°
90°
Σ
MAX2424 MAX2426
PHASE
SHIFTER
÷ 1/64/65
BIAS
RXOUT
DIV1 MOD
PREOUT
PREGND
TANK
TANK
VCOON
TXIN
TXIN
________________________________________________________Package Information
SSOP.EPS
Loading...