mga-725m4 Avago Technologies, mga-725m4 Datasheet - Page 17

• Manufacturer Part Number: mga-725m4
• Description: Low Noise Amplifer With Bypass Switch In Miniature Leadless Package
• Manufacturer: Avago Technologies

RF Bypass
For layouts using the source resistor method of biasing,
both of the ground terminals of the MGA-725M4 must be
well by-passed to maintain device stability.
Beginning with the package pad print in Figure 10, a RF
layout similar to the one shown in Figure 11 is a good
starting point for using the MGA-725M4 with capacitor-
bypassed ground terminals. It is a best practice to use
multiple vias to minimize overall ground path induc-
tance.
Two capacitors are used at each of the PCB pads for
both Pins 1 and 3. The value of the bypass capacitors is
a balance between providing a small reactance for good
RF grounding, yet not being so large that the capacitor’s
parasitics introduce undesirable resonances or loss.
Figure 11. Layout for RF Bypass.
Figure 13. Complete Amplifier with Component Reference Designators.
17
IN
CSP
R2 C0
R1
C1
C
C0
C3
L1
AVAGO
MGA-71,72
SW
C5
C4
C
9/00
SC
R3
C6
C
C2
RFC
C0
Out
If the source resistor biasing method is used, a ground
pad located near either Pin 1 or Pin 3 may be used to
connect the current-setting resistor (R
DC ground. If the R
ately adjacent to the MGA-725M4 (as may be the case
of dynamic control of the device’s linearity), then a small
series resistor (e.g. 10Ω) located near the ground terminal
will help de-Q the connection from the MGA-725M4 to
an external current-setting circuit.
PCB material
FR-4 or G-10 type dielectric materials are typical choices
for most low cost wireless applications using single or
multi-layer printed circuit boards. The thickness of single-
layer boards usually range from 0.020 to 0.031 inches.
Circuit boards should be constructed so that distance to
ground for RF signals are less than 0.031 inches. Using
PCB layer stacks that are greater than this are not recom-
mended due to excessive inductance in the vias.
Application Example
An example evaluation PCB layout for the MGA-725M4 is
shown in Figure 12. This evaluation circuit is designed for
operation from a +3-volts supply and includes provision
for a 2-bit DIP switch to set the state of the MGA-725M4.
For evaluation purposes, the 2-bit switch is used to set
the device to either of four states: (1) bypass mode-switch
bypasses the amplifier, (2) low noise amplifier mode–low
bias current, (3) and (4) driver amplifier modes–high bias
currents.
Figure 12. PCB Layout for Evaluation Circuit.
bias
resistor is not located immedi-
IN
AVAGO�
MGA-71,72�
4/00
bias
) directly to
Out