MAX2611
DC-to-Microwave, Low-Noise Amplifier
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_______________Detailed Description
The MAX2611 is a broadband amplifier with flat gain
and 50Ω input and output ports. Its small size and sim-
ple bias circuitry make it ideal for applications where
board space is limited.
__________Applications Information
External Components
As shown in the Typical Operating Circuit, the
MAX2611 is easy to use. Input and output series
capacitors may be necessary to block DC bias volt-
ages (generated by the MAX2611) from interacting with
adjacent circuitry. These capacitors must be large
enough to contribute negligible reactance in a 50Ω
system at the minimum operating frequency. Use the
following equation to calculate their minimum value:
where f (in MHz) is the minimum operating frequency.
Bias current is supplied to the MAX2611 through an
external resistor and optional RF choke connected
between V
CC
and the OUT pin. A bypass capacitor
from V
CC
to GND may be necessary to isolate the V
CC
line from other circuitry. The resistor value determines
the bias current from the following equation:
where V
D
is the device voltage, nominally 3.8V.
An optional RF choke can be added to improve the
MAX2611’s gain and output power. The choke should
be large enough to reduce the loading effect that the
bias resistor has on the amplifier output. This is a func-
tion of R
BIAS
, frequency of operation, and output
impedance.
Grounding
Proper grounding of the GND pins is essential. If the
PC board uses a topside RF ground, the GND pins
should be connected directly to it. For a board where
the ground plane is not on the component side, the
best technique is to connect the GND pins to it through
multiple plated through-holes.
PC Board Layout Example
An example PC board layout is given in Figure 1. It
uses FR-4 with 31mil layer thickness between the RF
lines and the ground plane. This board satisfies all the
above requirements.
