Rainbow Electronics MAX2645 - Manual (Page 9)

MAX2645
3.4GHz to 3.8GHz SiGe
Low-Noise Amplifier/PA Predriver
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Detailed Description
The MAX2645 is a versatile amplifier with high-gain,
high-linearity, and low-noise performance—features that
make it suitable for use as an LNA, high-linearity/low-
noise amplifier, PA predriver, or LO buffer in the 3.4GHz
to 3.8GHz frequency range. See Figure 1, MAX2645
Typical Application Circuit, for recommended compo-
nent values. A single external bias-setting resistor allows
the system designer to trade off linearity for reduced
supply current. A logic-level control reduces gain by a
25dB step to further improve input IP3 performance. A
low-power shutdown mode disables the device and
reduces current consumption to 0.1µA.
Bias Circuitry
The linearity and supply current of the MAX2645 are
externally programmable with a single resistor (R
BIAS )
placed from BIAS to GND. Larger resistor values result
in lower IP3 performance and lower supply current, while
smaller resistor values result in higher IP3 performance
and higher supply current. Use resistor values in the
15k
Ω to 25kΩ range, with a nominal value of 20kΩ
suitable for most applications. See Typical Operating
Characteristics for performance variation vs. R
BIAS
value.
Gain Step Control
The MAX2645 features a logic-level gain step control
input (GAIN) that places the device in high-gain or low-
gain mode. A logic-level high places the device in high-
gain mode, where the gain is 14.5dB. A logic-level low
places the device in low-gain/high-linearity mode, where
the gain is reduced to 10dB and the input IP3 perfor-
mance is increased.
Shutdown Control
The MAX2645 features a logic-level shutdown control
input. A logic high on SHDN enables the device for nor-
mal operation. A logic low on SHDN disables all device
functions and reduces supply current to 0.1µA.
Applications Information
RF Input
The RFIN port is internally biased and requires an exter-
nal DC-blocking capacitor. A matching network is
required for best performance. Figure 1 shows compo-
nent values optimized for best noise-figure performance,
low-noise figure, high-input IP3 performance, and high-
output P1dB performance in the 3.4GHz to 3.8GHz fre-
quency range. For matching to other frequencies, see
Tables 1 and 2.
Table 1. MAX2645 S-Parameters
S11 S21 S12 S22 FREQ
(MHz) MAG PHASE MAG PHASE MAG PHASE MAG PHASE
R BIAS = 20k Ω, V
CC = +3.3V, T A = +25 °C
3400 0.468 -149.8 5.061 -44.6 0.053 -55.5 0.660 -57.0
3450 0.466 -150.4 4.975 -46.3 0.058 -60.8 0.658 -58.4
3500 0.472 -151.6 5.098 -49.9 0.056 -64.6 0.661 -60.6
3550 0.469 -153.4 4.883 -53.7 0.054 -62.7 0.658 -63.0
3600 0.471 -154.6 4.814 -53.7 0.056 -64.4 0.647 -64.2
3650 0.477 -155.0 5.118 -57.4 0.058 -68.9 0.657 -66.2
3700 0.485 -156.6 4.769 -63.4 0.054 -70.5 0.657 -69.8
3750 0.484 -156.5 4.780 -62.3 0.058 -72.0 0.654 -70.9
3800 0.492 -157.0 4.939 -66.6 0.060 -75.4 0.654 -72.3
R BIAS = 15k Ω, V
CC = +5V, T A = +25 °C
3400 0.454 -146.6 5.350 -41.8 0.057 -51.3 0.651 -52.3
3450 0.457 -147.4 5.245 -43.5 0.061 -56.7 0.646 -53.7
3500 0.465 -147.9 5.375 -46.6 0.060 -61.2 0.654 -55.6
3550 0.468 -149.7 5.165 -50.3 0.057 -61.0 0.652 -58.3
3600 0.472 -150.5 5.066 -50.2 0.060 -62.7 0.645 -59.3
3650 0.481 -150.5 5.386 -53.4 0.063 -67.6 0.652 -60.7
3700 0.486 -152.2 5.040 -59.4 0.060 -67.8 0.648 -63.9
3750 0.486 -152.4 5.019 -58.3 0.062 -67.0 0.642 -64.8
3800 0.499 -152.6 5.207 -62.0 0.065 -73.3 0.643 -66.2