MAX2306/MAX2308/MAX2309
CDMA IF VGAs and I/Q Demodulators
with VCO and Synthesizer
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_______________Detailed Description
MAX2306
The MAX2306 is intended for dual-band (PCS and cel-
lular) and dual-mode code division multiple access
(CDMA) and FM applications (Figure 1). The device
includes an IF variable-gain amplifier, quadrature
demodulator, dual VCOs, and dual-frequency synthe-
sizers (Functional Diagram). Dual VCOs are provided
for applications using different IF frequencies for each
mode or band of operation. The analog FM output sig-
nal can be configured for conversion to the I channel,
or it may be converted in quadrature to both the I and
Q channels. The MAX2306’s operation modes are
described in Table 1. These modes are set by pro-
gramming the control register and setting logic levels
on control pins. If MODE is left floating, the internal reg-
ister controls the operation. If driven high or low, mode
will override certain register bits, as shown in Table 1.
MAX2308
The MAX2308 supports dual-band, triple mode with
common IF VCO. As with the MAX2306, the FM mode
can be configured for conversion to the I port or quad-
rature conversion to both the I and Q ports (Figure 2).
The MAX2308’s operational modes are described in
Table 2. These modes are set by programming the con-
trol register.
MAX2309
The MAX2309 quadrature demodulators are simplified
versions of the MAX2306 that can be used in single-
mode CDMA or triple mode using an external FM dis-
criminator (Figure 3). The MAX2309 VCO is optimized
for the 67MHz to 300MHz IF frequency range.
The MAX2309 includes a buffered output for the VCO.
The buffered VCO output can be used to support sys-
tems implementing traditional limiting IF stages for FM
demodulation in dual-mode phones as well as for the
transmit LO in TDD systems. This buffered output can
be configured for the VCO frequency (twice the IF fre-
quency) or one-half the VCO frequency (IF frequency).
The BUFEN pin enables this feature. A standby mode,
in which only the VCO and synthesizer are operational,
can be selected through the serial interface or the
STBY pin. The MAX2309’s operational modes are
described in Table 3. These modes are set by pro-
gramming the control register and/or setting logic levels
on control pins. If the control pins (STBY, BUFEN,
DIVSEL) are left floating, the internal register controls
the operational mode. If driven high or low, the control
pins will override certain register bits, as shown in
Table 3.
Applications Information
Variable-Gain Amplifier and Demodulator
The MAX2306 family provides a VGA with exceptional
gain range. The MAX2306/MAX2308 support multimode
applications with dual differential inputs, selectable with
the IN_SEL (IS) control bit. On the MAX2306, this func-
tion can be controlled with the MODE pin, which over-
rides the IS control bit. The VGA’s gain is controlled
over a 110dB range with the VGC pin. The output of the
VGA drives the RF ports of a quadrature demodulator.
The MAX2306/MAX2308 provide two types of FM
demodulation, controlled by the FM_TYPE (FT) control
bit. When FM_TYPE is “1,” the signal is passed through
both the I and Q signal paths for subsequent lowpass
filtering and A/D conversion at baseband. If FM_TYPE
is “0,” the FM signal is passed through the I mixer only.
Pin Description (continued)
