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MAX2248 Datasheet(Scheda tecnica) 8 Page - Maxim Integrated Products
Numero della parte
MAXIM [Maxim Integrated Products]
The output stage of the MAX2248 power amplifier is the
collector of a transistor. The DC bias and impedance
matching network are off-chip as shown in the Typical
Application Circuit/Functional Block Diagram. An off-chip
external network, as with most PA ICs, is used to achieve
higher efficiency and output power than is typically
achieved using low-Q on-chip matching elements.
The primary power-matching structure is a low-pass
network formed by the series transmission line section
T1 and the open-stub transmission line section T2. The
transmission line network acts like a series inductance
and shunt capacitance. T1 and T2 are expressed as
electrical lengths of a particular characteristic impedance
line, but could be designed with different impedance lines.
Choose the length of T2 to provide a short at the 2nd
harmonic frequency of the fundamental, and significantly
attenuate its amplitude at the output—1/4 wave at the
2nd harmonic frequency of 3.8GHz. The 3rd harmonic is
attenuated through the clever use of the parasitic capaci-
tance in the choke. This capacitance rolls off the choke
impedance at higher frequencies and appears as a low
impedance at the 3rd harmonic frequency. The output
series capacitor is used as a DC-blocking capacitor and a
final matching element. A value of 8pF is recommended.
For proper DC biasing, the PA requires a connection to
through an inductor, serving as a choke. Locate the
inductor on the load side of transmission line T1. The
recommended inductor value is 22nH. However, its value
is not critical but must provide an impedance that is
several hundred ohms. Choose an inductor with a self-
resonant frequency at, or slightly below, 1880MHz. The
inductor Q is not critical; a moderate Q (>25) is sufficient.
Remember to provide sufficient current-handling capability
for the inductor, in this case at least 200mA. Also, a 220pF
bypass capacitor is recommended at the supply-voltage
end of the inductor.
The off chip network connected to pin V
, shown in
the Typical Application Circuit/Functional Block Diagram,
forms part of the interstage match for the PA. The
performance of the PA is sensitive to the impedance
of this network. For best results, the trace should be a
50Ω transmission line, electrical length = 15° at 1.9GHz,
and the capacitor ground connection should follow a low
inductance path to IC GND.
Design the layout for the PA IC to be as compact as
possible to minimize the magnitude of parasitics. Connect
multiple vias from the ground plane as close to the ground
pins as possible. As already described, locate the capacitors
as close as possible to the IC supply voltage pin or supply
end of the series inductor. Place the ground end of these
capacitors near the IC GND pins to provide a low impedance
return path for the signal current.
-40°C to +85°C
-40°C to +85°C
+ Denotes a lead(Pb)-free/RoHS-compliant package.
T Denotes tape-and-reel.
Maxim Integrated │ 8
1.9GHz Power Amplifier
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