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发表于 2019-11-29 15:38
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汪洋大海 发表于 2019-9-6 09:31
+ h2 [9 T5 P1 p! Whttps://www.eda365.com/thread-188514-1-1.html
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$ S: S0 L0 T" J! T5 y) h( a }7 u奇怪，两者对比，偏差有点大。
* j. i) o+ ?) Y% l* Z' F- tThe Bridged-T Attenuator is another resistive attenuator design which is a variation on the standard symmetrical T-pad Attenuator." B" B# E& q# @& k
As its name implies, the bridged-T attenuator has an additional resistive element forming a bridged network across the two series resistors of the standard T-pad.
; I& k; k1 D. Q& S* V8 x* e$ }, v$ HThis additional resistive element enables the circuit to reduce the level of a signal by the required attenuation without changing the characteristic impedance of the circuit8 A: p% C1 n( ]5 c9 P. f
as the signal appears to “bridge” across the T-pad network. Also the two series resistances of the original T-pad are always equal to the input source and output load
1 k! i) ?( ~# ]3 g3 wimpedances.
. R0 H c2 K' ^$ g1 L {' A; cThe circuit for a “bridged-T attenuator”, ( T ) is given below.
# q2 Z x+ O0 o" V/ k+ f7 f- W: f0 U7 i# ]. n" X
) w' C& l" g& d4 X4 ~4 RResistor, R3 forms the bridge network across a standard T-pad attenuator. The two series resistors, R1 are chosen to equal the source/load line impedance. One major
+ c) M7 [( M7 `5 G G8 E- gadvantage of the bridged-T attenuator over its T-pad cousin, is that the bridged-T pad has a tendency to match itself to the transmissions lines characteristic impedance.
0 t+ K* O* R3 ^+ E; Y7 WHowever, one disadvantage of the bridged-T attenuator circuit is that the attenuator requires that its input or source impedance, ( Z ) equals its output or load impedance,! Z$ I4 L+ f: f8 G; B
( Z ) and therefore cannot be used for impedance matching.$ Y: e: _# |! |/ }
The design of a bridged-T attenuator is as simple as for the standard T-pad attenuator. The two series resistors are equal in value to the lines characteristic7 U8 K1 n2 X u! w# r1 ?* W: X
impedance and therefore require no calculation. Then the equations given to calculated the parallel shunt resistor and the additional bridging resistor of a bridged-T attenuator circuit used for impedance matching at any desired attenuation are given as: ~$ V+ M& q4 `4 w3 e' Q
Bridged-T Attenuator Equations:
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8 j+ A4 ~5 D/ Z! N+ d8 q5 H, \* s8 O8 K7 ]
where: K is the impedance factor, and Z is the source/load impedance.
7 J, d2 K, i3 Q5 ~, g/ m$ ]8 t4 M) \
8 [( D, l( ^: z2 Z1 }
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发表于 2019-9-3 08:25
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发表于 2019-9-6 09:30