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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
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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.2 G: g/ j# A. q8 C4 t' p' H
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.
- N2 K% q$ F! y) R: g6 sThis 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
* j# }% `$ A0 k6 Fas 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
6 x9 g- k; Z: Q% e8 i0 b7 Aimpedances. ( ^% q- }: k9 T Y8 I0 @
The circuit for a “bridged-T attenuator”, ( T ) is given below.: u) T; O- q" \# h, g
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* T, L9 R+ Z( N/ I5 OResistor, 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
, Z& V5 O% d- G& X2 Y+ S- iadvantage 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.
3 t ^( y! P2 a, u5 M; Z- nHowever, 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,2 u0 x x( m6 p9 t4 j* v
( Z ) and therefore cannot be used for impedance matching.
* O: ?1 g2 o. g; L" YThe 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* r; W5 X' B, @$ h: b
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:
9 n$ y# y1 x7 A( lBridged-T Attenuator Equations:( j- C( J2 Q; i! R% n
+ P4 c. _4 O! ?3 f# s4 E$ S$ S1 h {0 y# I' P& f$ b
where: K is the impedance factor, and Z is the source/load impedance.( J* {. u1 ]" O& b7 u$ v/ T
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发表于 2019-9-3 08:25
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发表于 2019-9-6 09:30