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MAX2451CSE
3V / Ultra-Low-Power Quadrature Demodulator
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_______________General DescriptionThe monolithic MAX2451 is a quadrature demodulator
with a supporting oscillator and divide-by-8 prescaler. It
operates from a single +3V supply and draws only
5.5mA. The demodulator accepts an amplified and fil-
tered IF signal in the 35MHz to 80MHz range, and
demodulates it into I and Q baseband signals with
51dB of voltage conversion gain. The IF input is termi-
nated with a 400Ωthin-film resistor for matching to an
external IF filter. The baseband outputs are fully differ-
ential and have 1.2Vp-p signal swings.
Pulling the CMOS-compatible ENABLE pin low shuts
down the MAX2451 and reduces the supply current to
less than 2µA, typical. To minimize spurious feedback,
the MAX2451’s internal oscillator is set at twice the IF
frequency via external tuning components. The
MAX2451 comes in a 16-pin narrow SO package.
________________________ApplicationsDigital Cordless Phones
GSM and North American Cellular Phones
Wireless LANs
Digital Communications
Pagers
____________________________FeaturesIntegrated Quadrature Phase ShiftersOn-Chip Oscillator (Requires External Tuning
Circuit)51dB Voltage Conversion Gain On-Chip Divide-by-8 PrescalerBaseband Output Bandwidth Up to 9MHzCMOS-Compatible Enable5.5mA Operating Supply Current
2µA Shutdown Supply Current
MAX2451, Ultra-Low-Power
Quadrature Demodulator
________________________________________________________________Maxim Integrated Products1
________________Functional Diagram
__________________Pin Configuration19-0493; Rev 0; 12/95
MAX2451, Ultra-Low-Power
Quadrature Demodulator_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS(VCC= LO_VCC= TANK= +2.7V to +3.3V, ENABLE = VCC- 0.4V, GND = LO_GND = 0V, I = I= Q = Q= IF = TANK = OPEN, = 0°C to +70°C, unless otherwise noted.)
AC ELECTRICAL CHARACTERISTICSVCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, fIF= 70.1MHz, VIF= 2.82mVp-p, TA= +25°C, 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:Guaranteed by design, not tested.
Note 2:fIF= 2 tones at 70.10MHz and 70.11MHz, VIF= 1.41mVp-p per tone.
Note 3:Oscillator frequencies up to 1GHz (500MHz IF) by externally overdriving (see Applications Information).
VCC, LO_VCCto GND............................................-0.3V to +4.5V
ENABLE, TANK, TANK, I, I,
Q, Qto GND.............................................-0.3V to (VCC+ 0.3V)
IF to GND...............................................................-0.3V to +1.5V
Continuous Power Dissipation (TA= +70°C)
Narrow SO (derate 8.70mW/°C above +70°C).............696mW
Operating Temperature Range...............................0°C to +70°C
Storage Temperature Range.............................-65°C to +165°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX2451, Ultra-Low-Power
Quadrature Demodulator
_______________________________________________________________________________________3SUPPLY CURRENT
vs. TEMPERATURE
MAX2451-01
TEMPERATURE (°C)
ICC
(mA)2030405060700
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATUREMAX2451-02
TEMPERATURE (°C)
SHUTDOWN I2030405060700
VOLTAGE CONVERSION GAIN vs.
TEMPERATURE AND SUPPLY VOLTAGE
MAX2451-03
GAIN (dBV)
VCC (V)
VOLTAGE CONVERSION
GAIN vs. IF FREQUENCYMAX2451-04
IF FREQUENCY (MHz)
GAIN (dBV)
PHASE AND AMPLITUDE
MATCHING vs. TEMPERATURE
MAX2451-05
TEMPERATURE (°C)
MATCHING (DEGREES OR dBV)
INTERMODULATION POWER
vs. TEMPERATURE
MAX2451-06
TEMPERATURE (°C)
INTERMODULATION (dBc)
__________________________________________Typical Operating Characteristics
(VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, fIF= 70.1MHz, VIF= 2.82mVp-p, TA= +25°C, unless otherwise noted.)
_______________Detailed DescriptionThe following sections describe each of the functional
blocks shown in the Functional Diagram. Also refer to
the Typical Application Block Diagram (Figure 1).
DemodulatorThe demodulator contains a single-ended-to-differential
converter, two Gilbert-cell multipliers, and two fixed
gain stages. Internally, IF is terminated with a 400Ω
resistor to GND. The IF input signal is AC coupled into
the input amplifier, which has 14dB of gain. This ampli-
fied IF signal is fed into the I and Q channel mixers for
demodulation. The multipliers mix the IF signal with the
quadrature LO signals, resulting in baseband I and Q
signals. The conversion gain of the multipliers is 15dB.
These signals are further amplified by 21dB by the
baseband amplifiers. The baseband amplifier chains
are DC coupled.
Local OscillatorThe local-oscillator section is formed by an emitter-cou-
pled differential pair. Figure 2 shows the local-oscillator
equivalent circuit schematic. An external LC resonant
tank determines the oscillation frequency, and the Q of
this resonant tank affects the oscillator phase noise.
The oscillation frequency is twice the IF frequency, for
easy generation of quadrature signals.
The oscillator may be overdriven by an external source.
The source should be AC coupled into TANK/TANK, and
should provide 200mVp-p levels. A choke (typically
2.2µH) is required between TANK and TANK. Differential
input impedance at TANK/TANKis 10kΩ. For single-
ended drive, connect an AC bypass capacitor (1000pF)
from TANKto GND, and AC couple TANK to the source.
The oscillator can be overdriven at frequencies up to
1GHz (500MHz IF), but conversion gain and prescaler
output levels will be somewhat reduced.
MAX2451, Ultra-Low-Power
Quadrature Demodulator_______________________________________________________________________________________
_____________________Pin DescriptionFigure 1. Typical Application Block Diagram
Quadrature Phase GeneratorThe quadrature phase generator uses two latches to
divide the local-oscillator frequency by two, and gener-
ates two precise quadrature signals. Internal limiting
amplifiers shape the signals to approximate square
waves to drive the Gilbert-cell mixers. The inphase sig-
nal (at half the local oscillator frequency) is further
divided by four for the prescaler output.
PrescalerThe prescaler output, PRE_OUT, is buffered and swings
typically 0.35Vp-p with a 10kΩand 6pF load. It can be
AC coupled to the input of a frequency synthesizer.
Master BiasDuring normal operation, ENABLE should be above
VCC- 0.4V. Pulling the ENABLE input low shuts off the
master bias and reduces the circuit current to typically
2µA. The master bias section includes a bandgap ref-
erence generator and a PTAT (Proportional To Absolute
Temperature) current generator.
__________Applications InformationFigure 3 shows the implementation of a resonant tank
circuit. The inductor, two capacitors, and a dual varac-
tor form the oscillator’s resonant circuit. In Figure 3, the
oscillator frequency ranges from 130MHz to 160MHz.
To ensure reliable start-up, the inductor is directly con-
nected across the local oscillator’s tank ports. The two
33pF capacitors affect the Q of the resonant circuit.
Other values may be chosen to meet individual appli-
cation requirements. The oscillation frequency can be
determined using the following formula:
where CSTRAY= parasitic capacitance and LSTRAY=
parasitic inductance.
To alter the oscillation frequency range, change the
inductance, the capacitance, or both. For best phase-
noise performance, keep the Q of the resonant tank as
high as possible:
where REQ≈10kΩ(Figure 2).
The oscillation frequency can be changed by altering
the control voltage, VCTRL.
MAX2451, Ultra-Low-Power
Quadrature Demodulator
_______________________________________________________________________________________5Figure 2. Local-Oscillator Equivalent Circuit
Figure 3. Typical Resonant Tank Circuit
MAX2451, Ultra-Low-Power
Quadrature Demodulator
________________________________________________________Package InformationMaxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-76001995 Maxim Integrated Products Printed USAis a registered trademark of Maxim Integrated Products.
