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标题: Attenuator Bridged T Excel計算器 [打印本页]
作者: pprichard    时间: 2019-9-3 08:25
标题: Attenuator Bridged T Excel計算器
可以簡單地輸入特性阻抗計算出需要的電阻值，或輸入電阻值計算出特性阻抗..5 I9 @. I' l# X' \2 k* p# V3 a

Attenuator Bridged T.rar

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作者: 汪洋大海    时间: 2019-9-6 09:30

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作者: 汪洋大海    时间: 2019-9-6 09:31
https://www.eda365.com/thread-188514-1-1.html
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& Y; _" A$ @1 W2 g奇怪，两者对比，偏差有点大。
作者: pprichard    时间: 2019-11-29 15:38
汪洋大海 发表于 2019-9-6 09:319 D" [+ f. T# g/ Y
https://www.eda365.com/thread-188514-1-1.html& v/ ]- A. ~' y; h2 R
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奇怪，两者对比，偏差有点大。

+ y& _/ g8 B3 W+ a! U0 MThe Bridged-T Attenuator is another resistive attenuator design which is a variation on the standard symmetrical T-pad Attenuator.
; d! Q" Q3 Q4 z$ o0 g# \6 v2 N+ oAs 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.' U: o2 L: i7 p4 B
This additional resistive element enables the circuit to reduce the level of a signal by the required attenuation without changing the characteristic impedance of the circuit
5 c, t6 g: m% [1 ?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 load5 _( r. q/ A. v8 o; t: l
impedances. ! ]! x$ f- x/ U: t
The circuit for a “bridged-T attenuator”, ( T ) is given below.& ?* s2 U" \9 n7 \5 ^

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' D0 h" ^  C& h1 t! JResistor, 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
2 J! U; G$ Y  T* s$ [5 aadvantage 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.
( O1 Q' ^8 G- y. w6 HHowever, 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,1 X% H3 l& {- n! Q/ G, {2 i) p9 y9 W2 D
( Z ) and therefore cannot be used for impedance matching.- u) z  w' {- T9 s- ?* q
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 characteristic4 m0 i  `0 d( [5 z7 ]; A
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:
: ^; f8 v. Z* m/ a) H: M5 ZBridged-T Attenuator Equations:6 v5 M3 q5 ^6 w1 d. v

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where: K is the impedance factor, and Z is the source/load impedance.
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作者: pprichard    时间: 2019-12-3 17:29
汪洋大海 发表于 2019-9-6 09:31
9 `8 q$ }; N7 w* `5 ?5 O) g$ Ahttps://www.eda365.com/thread-188514-1-1.html5 j' T" G' l- \% J5 U3 o3 Y6 A

- ~8 ?; X! b" T0 h1 }9 y) Q  I% w奇怪，两者对比，偏差有点大。
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Bridged-T Attenuator Example
8 I, a1 |3 M: C$ P, cA bridged-T attenuator is required to reduce the level of an 8Ω audio signal line by
' C  R0 P% d6 y7 _" G4dB. Calculate the values of the resistors required.
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( n0 ~5 K! J) k# gThen resistors R1 are equal to the line impedance of 8Ω, resistor R2 is equal to 13.7Ω. {: m. T- i+ m8 t0 t
and the bridging resistor R3 is equal to 4.7Ω, or the nearest preferred values.$ \* h0 t$ o: X! B
As with the standard T-pad attenuator, as the amount of attenuation required by the
% W! M) g7 Y: y/ `. b! g0 f4 Ccircuit increases, the series bridge impedance value of resistor R3 also increase while3 K3 e8 B2 X' C1 G
the parallel shunt impedance value of resistor R2 decreases. This is characteristic of a
/ D/ g' C# ]6 l1 d4 hsymmetrical bridged-T attenuator circuit used between equal impedances.
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