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PDF MAX2424 Data sheet ( Hoja de datos )
| Número de pieza | MAX2424 | |
| Descripción | 900MHz Image-Reject Receivers with Transmit Mixer | |
| Fabricantes | Maxim Integrated | |
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19-1350 Rev 2; 2/99
EVFAOLLULAOTWIOSNDKAITTAMSAHNEUEATL
900MHz Image-Reject Receivers
with Transmit Mixer
________________General Description
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.
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 trans-
mit 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-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.
The MAX2424/MAX2426 come in a 28-pin SSOP pack-
age.
________________________Applications
Cordless Phones
Wireless Telemetry
Wireless Networks
Spread-Spectrum Communications
Two-Way Paging
Functional Diagram appears at end of data sheet.
____________________________Features
o Receive Mixer with 35dB Image Rejection
o Adjustable-Gain LNA
o Up to +2dBm Combined Receiver Input IP3
o 4dB Combined Receiver Noise Figure
o Optimized for Common Receiver IF Frequencies:
10.7MHz (MAX2424)
70MHz (MAX2426)
o PA Predriver Provides up to 0dBm
o Low Current Consumption: 23mA Receive
20mA Transmit
9.5mA Oscillator
o 0.5µA Shutdown Mode
o Operates from Single +2.7V to +4.8V Supply
_______________Ordering Information
PART
MAX2424EAI
MAX2426EAI
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 SSOP
28 SSOP
___________________Pin Configuration
TOP VIEW
VCC 1
CAP1 2
RXOUT 3
GND 4
RXIN 5
VCC 6
GND 7
GND 8
TXOUT 9
LNAGAIN 10
VCC 11
TXIN 12
TXIN 13
CAP2 14
MAX2424
MAX2426
SSOP
28 GND
27 GND
26 GND
25 TANK
24 TANK
23 VCC
22 VCC
21 PREOUT
20 PREGND
19 MOD
18 DIV1
17 VCOON
16 RXON
15 TXON
________________________________________________________________ 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.
1 page  
900MHz Image-Reject Receiver
with Transmit Mixer
__________________________________________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 = VTXIN = 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.)
42
40
38
36
34
32
30
28
26
24
-40
RECEIVER SUPPLY CURRENT
vs. TEMPERATURE
VCC = 4.8V
VCC = 3.3V
VCC = 2.7V
RXON = VCC
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
-20 0 20 40 60 80
TEMPERATURE (°C)
25
20
15
10
5
0
-5
-10
-15
-20
0
RECEIVER GAIN vs. LNAGAIN
LNA
LNA PARTIALLY
OFF BIASED
ADJUSTABLE MAX
GAIN GAIN
AVOID
THIS
REGION
RXON = VCC
0.5 1.0 1.5
LNAGAIN VOLTAGE (V)
2.0
MAX2424
RECEIVER GAIN vs. TEMPERATURE
LNAGAIN = VCC
26 RXON = VCC
24 VCC = 4.8V
22
VCC = 2.7V
VCC = 3.3V
20
18
-40 -20
0 20 40 60
TEMPERATURE (°C)
80
TRANSMITTER SUPPLY CURRENT
vs. TEMPERATURE
39
37
35
33 VCC = 4.8V
31 VCC = 3.3V
29
27
VCC = 2.7V
25
23
21
-40
-20
TXON = VCC
PREGND = UNCONNECTED
INCLUDES OSCILLATOR
CURRENT
0 20 40 60
TEMPERATURE (°C)
80
RECEIVER INPUT IP3 vs. LNAGAIN
5
LNA LNA ADJUSTABLE MAX
OFF PARTIALLY GAIN GAIN
0 BIASED
AVOID
-5 THIS
REGION
-10
-15
-20
0
RXON = VCC
0.5 1.0 1.5
LNAGAIN VOLTAGE (V)
2.0
RECEIVER NOISE FIGURE vs.
TEMPERATURE AND SUPPLY VOLTAGE
5.5
LNAGAIN = VCC
RXON = VCC
5.0 DIV1 = VCC
VCC = 4.8V
4.5
VCC = 3.3V
4.0
VCC = 2.7V
3.5
3.0
-40 -20
0 20 40 60
TEMPERATURE (°C)
80
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
4.5
VCOON = GND
4.0
3.5
3.0
2.5
2.0 VCC = 4.8V
1.5
1.0 VCC = 3.3V
0.5
0
-40
-20
VCC = 2.7V
0 20 40 60
TEMPERATURE (°C)
80
RECEIVER NOISE FIGURE
vs. LNAGAIN
40
35
LNA ADJUSTABLE MAX
LNA PARTIALLY GAIN
GAIN
30 OFF BIASED
25
20
15
10
5
0
0
AVOID
THIS
REGION
RXON = VCC
DIV1 = VCC
0.5 1.0 1.5
LNAGAIN VOLTAGE (V)
2.0
RECEIVER INPUT IP3
vs. TEMPERATURE
-6
-8 VLNAGAIN = 1V
-10
-12
-14
-16
-18
-20
-40
VLNAGAIN = 2V
RXON = VCC
-20 0 20 40 60 80
TEMPERATURE (°C)
_______________________________________________________________________________________ 5
5 Page 
900MHz Image-Reject Receiver
with Transmit Mixer
VCC
R1 i
TXIN
MAX2424
MAX2426
1.5µA
R2
TXIN
2M
1.5µA
R3
RT = R1 + R2 + R3
VDIFF = VTXIN - VTXIN
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 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 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 RT
VCC
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.
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).
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.
The LO may be overdriven in applications where an
external signal is available. The external LO signal
should be about 0dBm from 50Ω, and should be AC
coupled into either the TANK or TANK pin. Both TANK
and TANK require pull-up resistors to VCC. See the
Applications Information section 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 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
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MAX2424.PDF ] | |
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