Rainbow Electronics MAX2056 - Manual (Page 11)

Applications Information
Analog Attenuation Control
A single input voltage at the V CNTL pin adjusts the gain
of the MAX2056. Up to 22dB of gain-control range is
provided through a single attenuator. At the maximum
gain setting, each attenuator’s insertion loss is approxi-
mately 1.7dB. With the single attenuator at the maxi-
mum gain setting, the device provides a nominal
15.5dB of cascaded gain and 4.5dB of cascaded noise
figure.
If a larger gain-control range is desired, a second on-
chip attenuator can be connected in the signal path to
provide an additional 22dB of gain-control range. With
the second attenuator connected at the maximum gain
setting, the device typically exhibits 13.8dB of cascad-
ed gain. Note that the V
CNTL pin simultaneously adjusts
both on-chip attenuators. The V CNTL input voltage dri-
ves a high-impedance load (>250k
Ω). It is suggested
that a current-limiting resistor be included in series with
this connection to limit the input current to less than
40mA should the control voltage be applied when V
CC
is not present. A series resistor of greater than 200 Ω
will provide complete protection for 5V control voltage
ranges. Limit V
CNTL input voltages to a 1.0V to 4.5V
range when V CC is present to ensure the reliability
of the device.
Amplifier Bias Current
The MAX2056 integrates a two-stage amplifier to simul-
taneously provide high gain and high IP3. Optimal per-
formance is obtained when R1 and R2 are equal to
1.2k
Ω and 3.92kΩ, respectively. The typical supply cur-
rent is 136mA and the typical output IP3 is 39dBm
under these conditions.
Increasing R1 and R2 from the nominal values of 1.2k Ω
and 3.92k
Ω reduces the bias current of each amplifier
stage, which reduces the total power consumption and
IP3 of the device. This feature can be utilized to further
decrease power consumption for applications that do
not require high IP3.
Layout Considerations
A properly designed PC board is an essential part of
any RF/microwave circuit. Keep RF signal lines as short
as possible to reduce losses, radiation, and induc-
tance. For best performance, route the ground-pin
traces directly to the exposed pad underneath the
package. This pad MUST be connected to the ground
plane of the board by using multiple vias under the
device to provide the best RF and thermal conduction
path. Solder the exposed pad on the bottom of the
device package to a PC board exposed pad.
Power-Supply Bypassing
Proper voltage-supply bypassing is essential for high-
frequency circuit stability. Bypass each V
CC pin with
capacitors placed as close to the device as possible.
Place the smallest capacitor closest to the device. Refer
to the MAX2056 evaluation kit data sheet for more details.
Exposed Paddle RF and Thermal
Considerations
The EP of the MAX2056’s 36-pin thin QFN-EP package
provides a low-thermal-resistance path to the die. It is
important that the PC board on which the IC is mounted
be designed to conduct heat from this contact. In addi-
tion, the EP provides a low-inductance RF ground path
for the device.
The EP MUST be soldered to a ground plane on the PC
board either directly or through an array of plated via
holes. Soldering the pad to ground is also critical for
efficient heat transfer. Use a solid ground plane wher-
ever possible.
MAX2056
800MHz to 1000MHz Variable-Gain
Amplifier with Analog Gain Control
______________________________________________________________________________________ 11
Table 1. Typical Application Circuit
Components Values
DESIGNATION VALUE TYPE
C1, C3, C5, C10 47pF Microwave capacitors (0402)
C2, C4, C6, C8, C9 1000pF Microwave capacitors (0402)
C7 3.9pF Microwave capacitor (0402)
C13, C14, C15 0.1µF Microwave capacitors (0603)
R1 1.2k Ω ±1% resistor (0402)
R2 3.92k Ω ±1% resistor (0402)