Attenuator Bridged T Excel計算器

pprichard

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..

汪洋大海

汪洋大海

https://www.eda365.com/thread-188514-1-1.html

奇怪，两者对比，偏差有点大。

pprichard

汪洋大海 发表于 2019-9-6 09:31
8 M$ \9 \3 O/ xhttps://www.eda365.com/thread-188514-1-1.html
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奇怪，两者对比，偏差有点大。

The Bridged-T Attenuator is another resistive attenuator design which is a variation on the standard symmetrical T-pad Attenuator.
" g! X1 r" \5 K2 T: y4 SAs 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.
9 o; x+ i7 B. \" K3 W5 B9 uThis 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
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
$ K: p4 ^3 }& Y+ l2 V. |) @impedances.
9 U: ^& d, m  b' d3 PThe circuit for a “bridged-T attenuator”, ( T ) is given below.
- v3 e5 t+ f& Q% R

3 i6 J4 N) a% Z4 \) \& |2 I* @Resistor, 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
1 u1 b/ u' d9 L: c4 Eadvantage 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.
However, 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 ) and therefore cannot be used for impedance matching.
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 characteristic
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:
  `" f- \* ^; v0 l8 J: XBridged-T Attenuator Equations:

6 s( H# e- i+ D+ _2 Z
+ H$ j' R  T: m4 O+ ?where: K is the impedance factor, and Z is the source/load impedance.
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pprichard

汪洋大海 发表于 2019-9-6 09:31
3 v& D. @% l6 v+ G5 L! {; {, e' l$ r' \/ Khttps://www.eda365.com/thread-188514-1-1.html

$ q- N- J6 ], h3 s. n8 ^) o: s/ x奇怪，两者对比，偏差有点大。

Bridged-T Attenuator Example
: T" n2 g1 e, W" zA bridged-T attenuator is required to reduce the level of an 8Ω audio signal line by
4dB. Calculate the values of the resistors required.

Then resistors R1 are equal to the line impedance of 8Ω, resistor R2 is equal to 13.7Ω
5 V  P' c1 r. ?+ ^+ Rand the bridging resistor R3 is equal to 4.7Ω, or the nearest preferred values.
% T1 a/ e+ f2 R+ R# L. SAs with the standard T-pad attenuator, as the amount of attenuation required by the
0 P2 z. b' q9 w. ncircuit increases, the series bridge impedance value of resistor R3 also increase while
7 [; o8 g. X1 ?+ N3 V: v" `4 \the parallel shunt impedance value of resistor R2 decreases. This is characteristic of a
6 w5 a# ^# }+ Z* Msymmetrical bridged-T attenuator circuit used between equal impedances.
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