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參數(shù)資料
| 型號： | AN3833 |
| 英文描述： | RF inductor, ceramic core, 5% tol, SMT, RoHS |
| 中文描述： | DW9249鋸面向DECT帶通濾波器 |
| 文件頁數(shù)： | 1/5頁 |
| 文件大小： | 65K |
| 代理商： | AN3833 |
AN4833 Application Note
1/5
Figure 1: Block Diagram of a Typical 2GHz Radio
SELECTION OF IF FREQUENCY:
The DW9249 is a S.A.W. Bandpass Filter designed
specifically for use in Digital European Cordless Telephones
(D.E.C.T.). A circuit schematic of a typical DECT receiver
architecture is shown in Fig. 1. In this design a superhet
philosophy is employed, using an Intermediate frequency (I.F.)
at typically 110 to 112 MHz. Early designs of DECT receivers
used 110.592 MHz but more recently this has been avoided
owing to 6th or 8th harmonic leak through from either an
18.432MHz or 13.824 MHz reference oscillator. For this
reason 112.32 MHz has now become a preferred standard.
DECT DESIGN CONSIDERATIONS:
The DW9249 operates at 112.32MHz and has an minimum
operating 3dB bandwidth of 1200 KHz. The modulation rate
and type specified within DECT demand an operating
bandwidth of
±
576 KHz under all conditions. Furthermore the
DECT standard specifies a co-channel performance of 10dB
and 15dB adjacent channel interference performance. These
two requirements should be met allowing for all manufacturing,
ageing and temperature tolerances. Overall allowance for
these parameters, translates into a tight specification on the
filter roll-off (shaping) characteristics.
An operating temperature range of -20
°
C to +85
°
C is
recommended with a minimum requirement of 0
°
C to +40
°
C. It
is for this reason that ST Quartz is used by Dynex
Semiconductor as the substrate medium. Lithium Niobate
based devices have extremely poor temperature performance
with Lithium Tantalate being only marginally better. If the latter
of these materials were to be employed then operational
performance could only be guaranteed over the restricted
temperature of 0
°
C to 40
°
C. For this reason Lithium Tantalate
based devices have been primarily restricted to use in Test
Systems enjoying a controlled climatic environment. On the
other hand, the advantages from the use of Quartz as a
substrate medium substantially improves the device
manufacturability and co-channel/adjacent channel
interference performance.
SAW FILTER DESIGN OPTIONS:
The next issue in the choice of design of Filter for DECT
filtering has been the trade-offs between the demands for low
Insertion Loss and low Group Delay ripple. Unlike many pure
analogue communications systems, particular attention must
be paid in digital communications to the phase or group delay
ripple parameters of components. Phase distortion will
10.368MHz
Std IF-IC
112.32MHz
PLL
1881.792-
1897.344MHz
1880-
1900MHz
PLL
13.824MHz
(Ref Osc)
1881.792-
1897.344MHz
101.952MHz
TX- Key
TX Data
1783MHz
±
15MHz
101.952MHz
13.824MHz
(Ref Osc)
tau
Data
Slicer
RSSI
AN3833
SAW Bandpass Filter for DECT
Application Note
AN3833-2.0 January 2000
Replaces July 1993 version, AN3833-1.2
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