參數(shù)資料
型號: MAX1479ATE+T
廠商: Maxim Integrated
文件頁數(shù): 8/10頁
文件大?。?/td> 265K
描述: IC TRANSM ASK/FSK 16-TQFN
其它有關(guān)文件: Automotive Product Guide
產(chǎn)品培訓(xùn)模塊: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
標(biāo)準(zhǔn)包裝: 2,500
頻率: 300MHz ~ 450MHz
應(yīng)用: ISM,車庫門開啟器,RKE
調(diào)制或協(xié)議: ASK,F(xiàn)SK,OOK
數(shù)據(jù)傳輸率 - 最大: 100 kbps
功率 - 輸出: 2.7dBm ~ 16.1dBm
電流 - 傳輸: 6.7mA ~ 10.5mA
數(shù)據(jù)接口: PCB,表面貼裝
天線連接器: PCB,表面貼裝
電源電壓: 2.1 V ~ 3.6 V
工作溫度: -40°C ~ 125°C
封裝/外殼: 16-WFQFN 裸露焊盤
包裝: 帶卷 (TR)
300MHz to 450MHz Low-Power,
Crystal-Based +10dBm ASK/FSK Transmitter
8  _______________________________________________________________________________________
Output Matching to
PCB Loop Antenna
In most applications, the MAX1479 power-amplifier out-
put has to be impedance matched to a small-loop
antenna. The antenna is usually fabricated out of a cop-
per trace on a PCB in a rectangular, circular, or square
pattern. The antenna has an impedance that consists of
a lossy component and a radiative component. To
achieve high radiating efficiency, the radiative compo-
nent should be as high as possible, while minimizing
the lossy component. In addition, the loop antenna has
an inherent loop inductance associated with it (assum-
ing the antenna is terminated to ground). For example,
in a typical application, the radiative impedance is less
than 0.5? the lossy impedance is less than 0.7? and
the inductance is approximately 50nH to 100nH.
The objective of the matching network is to match the
power-amplifier output to the impedance of the small-
loop antenna. The matching components thus tune out
the loop inductance and transform the low radiative
and resistive parts of the antenna into the much higher
value of the PA output. This gives higher efficiency. The
low radiative and lossy components of the small-loop
antenna result in a higher Q matching network than the
50?network; thus, the harmonics are lower.
Layout Considerations
A properly designed PCB is an essential part of any
RF/microwave circuit. On the power-amplifier output,
use controlled-impedance lines and keep them as short
as possible to minimize losses and radiation.
Keeping the traces short reduces parasitic inductance.
Generally, 1in of PCB trace adds about 20nH of para-
sitic inductance. Parasitic inductance can have a dra-
matic effect on the effective inductance. For example, a
0.5in trace connecting a 100nH inductor adds an extra
10nH of inductance, or 10%.
To reduce the parasitic inductance, use wider traces
and a solid ground or power plane below the signal
traces. Using a solid ground plane can reduce the par-
asitic inductance from approximately 20nH/in to 7nH/in.
Also, use low-inductance connections to ground on all
GND pins and place decoupling capacitors close to all
V
DD
connections.
COMPONENT
VALUE FOR
f
RF
 = 433MHz
VALUE FOR
f
RF
 = 315MHz
L1
22nH
27nH
L3
18nH
22nH
C1
6.8pF
15pF
C2
10pF
22pF
C3
10nF
10nF
C4
680pF
680pF
C6
6.8pF
15pF
C8
220pF
220pF
C10
10nF
10nF
C11
220pF
220pF
C12
220pF
220pF
C14
100pF
100pF
C15
100  F
100  F
Table 3. Component Values for Typical
Application Circuit
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