MAX2335
Detailed Description
Low-Noise Amplifiers (LNAs)
The MAX2335’s LNA gain and linearity characteristics
can be adjusted using the MODE[2:0] inputs. See
Table 1 for the pin settings for various operating
modes. Use high-gain, high-linearity mode (HGHL)
when extra-high linearity is required for cross-modula-
tion suppression in the presence of strong interfering
signals (e.g., when the system transmitter is on). Use
high-gain, low-linearity mode (HGLL) when the trans-
mitter is off and cross-modulation is not a concern, and
use low-gain mode (LG) when receiving large signals.
R
LNA
can be adjusted to vary the current and linearity
of the HGHL LNA. R
BIAS
adjusts the current and the lin-
earity of the HGLL and LG LNA.
Downconverter
The mixer requires a DC-blocking capacitor at the input
and pullup inductors at the output. The DC-blocking
capacitors and pullup inductors can be designed to be
part of the matching circuits. See Table 1 for the MODE
settings for various operating modes.
LO Output Buffer
The LO output buffer is internally matched to 50Ω and
includes a DC-blocking capacitor. Enable the buffer by
driving the BUFFEN input high; disable the buffer by
driving the BUFFEN input low. The frequency of the
buffer output is equal to the LO frequency if the LO/2
input is driven low, or equal to the LO frequency divid-
ed by two if LO/2 is driven high.
Applications Information
Cascaded LNA/Mixer Performance
The LNA and mixer design optimizes cascaded perfor-
mance in all gain and linearity modes. In HGHL mode,
both the LNA and mixer have a low noise figure, high
gain, and high linearity. The LNA has high gain to mini-
mize the noise contribution of the mixer, thus increasing
the receiver’s sensitivity, and the LNA has high linearity
for cross-modulation suppression. The HGLL mode is
used when the transmitter is off and cross-modulation
is not a concern. In LG mode, the received signal is
strong enough that linearity is the primary concern. The
LNA gain is reduced to achieve higher system linearity.
S-Parameters
The S-parameters in Tables 2, 3, and 4 can be used to
design the RF matching circuits.
450MHz CDMA/OFDM LNA/Mixer
6 _______________________________________________________________________________________
