MAX2450 Ver la hoja de datos (PDF) - Maxim Integrated
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MAX2450 Datasheet PDF : 8 Pages
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3V, Ultra-Low-Power Quadrature
Modulator/Demodulator
pression. Alternatively, a differential DAC may be con-
nected without AC coupling, as long as a common-
mode voltage range of 1.25V to 1.75V is maintained.
For single-ended drive, connect I_IN and Q_IN via AC-
coupling capacitors (0.1µF) to GND.
The IF output is designed to drive a high impedance
(> 20kΩ), such as an IF buffer or an upconverter
mixer. IF_OUT/IF_OUT must be AC coupled to the
load. Impedances as low as 200Ω can be driven with a
decrease in output amplitude (Figure 3). To drive a sin-
gle-ended load, AC couple and terminate IF_OUT with
a resistive load equal to the load at IF_OUT.
Master Bias
During normal operation, ENABLE should remain above
VCC - 0.4V. Pulling the ENABLE input low shuts off the
master bias and reduces the circuit current to less than
2µA. The master bias section includes a bandgap ref-
erence generator and a PTAT (Proportional To Absolute
Temperature) current generator.
__________Applications Information
Figure 4 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 4, 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. Use the following formula to deter-
mine the oscillation frequency:
where
fo =
1
2π LEQCEQ
CEQ =
1+
1
1+
2
+ CSTRAY
C1 C2 CVAR
and
LEQ = L + LSTRAY
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:
Q = REQ CEQ
LEQ
where REQ ≈ 10kΩ (Figure 2).
The oscillation frequency can be changed by altering
the control voltage, VCTRL.
TANK
C1 = 33pF
47k
L = 100nH
TANK
C2 = 33pF
1/2 KV1410
10k
1/2 KV1410
47k
0.1µF
VCTRL
Figure 4. Typical Resonant Tank Circuit
Maxim 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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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