MAX2754EUA Maxim Integrated Products, MAX2754EUA Datasheet - Page 6

• Manufacturer Part Number: MAX2754EUA
• Description: Timers & Support Products 1.2GHz Monolithic VC O with Linear Modula
• Manufacturer: Maxim Integrated Products

The tuning input is typically connected to the output of
the PLL loop filter. The loop filter provides an appropri-
ately low-impedance source. Incorporate an extra RC
filter stage to reduce high-frequency noise and spuri-
ous signals. Any excess noise on the tuning input is
directly translated into FM noise, which can degrade
the phase-noise performance of the oscillator.
Therefore, it is important to minimize the noise intro-
duced on the tuning input. A simple RC filter with low
corner frequency is needed during testing to filter the
noise present on the voltage source driving the tuning
line.
The MAX2754 is designed for use in FSK applications
operating in the 2.4GHz to 2.5GHz ISM band. Specifically,
it is targeted for those systems which utilize a direct TX
modulation architecture in which the VCO is directly modu-
lated with the data signal during the transmit (TX) mode.
The VCO in these systems runs at half the RF output
frequency and is used in conjunction with a frequency
doubler to produce the final LO signal for both RX and
TX modes of operation.
1.2GHz VCO with Linear
Modulation Input
Figure 2. Typical Application Circuit for Two-Level FSK
6
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Applications Information
INVERTED
SIGNAL
CMOS
Two-Level FSK Applications
R2
R4
V
CC
R1
R3
FILTER
MOD.
LOOP FILTER
FROM PLL
330nF
Tune Input
VREG
TUNE
GND1
MOD
MAX2754
Figure 2 shows a typical applications circuit. To com-
pute R1, R2, R3, and R4, determine the modulation
voltage center point (V
required modulation voltage deviation as follows:
Figure 1. Modulation Frequency Deviations Characteristics
REG AND BIAS
MODULATION
OSCILLATOR
INTERFACE
f
f
LINEAR
NOM
NOM
CORE
+ f
- f
f
MOD
MOD
NOM
0.5
MODULATION VOLTAGE, V
SHDN
GND2
OUT
V
CC
MODB
1.0
V
FROM BASEBAND
DIGITAL
CONTROLLER
OUT TO
MIXER/
SYNTHESIZER
CC
330nF
1.5
= +1.4V). Compute the
MOD
2.0
(V)
2.5