82:
259:, the losses of energy in conductors due to the reactive component of the impedance can be significant. These losses manifest themselves in a phenomenon called phase imbalance, where the current is out of phase (lagging behind or ahead) with the voltage. Therefore, the product of the current and the voltage is less than what it would be if the current and voltage were in phase. With DC sources, reactive circuits have no impact, therefore power factor correction is not necessary.
843:. The losses due to input impedance (loss) in these circuits will be minimized, and the voltage at the input of the amplifier will be close to voltage as if the amplifier circuit was not connected. When a device whose input impedance could cause significant degradation of the signal is used, often a device with a high input impedance and a low output impedance is used to minimize its effects.
880:). Pre-amplifiers designed for high input impedance may have a slightly higher effective noise voltage at the input (while providing a low effective noise current), and so slightly more noisy than an amplifier designed for a specific low-impedance source, but in general a relatively low-impedance source configuration will be more resistant to noise (particularly
576:
262:
For a circuit to be modelled with an ideal source, output impedance, and input impedance; the circuit's input reactance can be sized to be the negative of the output reactance at the source. In this scenario, the reactive component of the input impedance cancels the reactive component of the output
144:
The values of the input and output impedance are often used to evaluate the electrical efficiency of networks by breaking them up into multiple stages and evaluating the efficiency of the interaction between each stage independently. To minimize electrical losses, the output impedance of the signal
112:
If the load network were replaced by a device with an output impedance equal to the input impedance of the load network (equivalent circuit), the characteristics of the source-load network would be the same from the perspective of the connection point. So, the voltage across and the current through
895:
In analog video circuits, impedance mismatch can cause "ghosting", where the time-delayed echo of the principal image appears as a weak and displaced image (typically to the right of the principal image). In high-speed digital systems, such as HD video, reflections result in interference and
759:. Since the characteristic impedance for a homogeneous transmission line is based on geometry alone and is therefore constant, and the load impedance can be measured independently, the matching condition holds regardless of the placement of the load (before or after the transmission line).
377:
360:
transfer states that for a given source maximum power will be transferred when the resistance of the source is equal to the resistance of the load and the power factor is corrected by canceling out the reactance. When this occurs the circuit is said to be
346:
145:
should be insignificant in comparison to the input impedance of the network being connected, as the gain is equivalent to the ratio of the input impedance to the total impedance (input impedance + output impedance). In this case,
131:
If one were to create a circuit with equivalent properties across the input terminals by placing the input impedance across the load of the circuit and the output impedance in series with the signal source,
571:{\displaystyle {\begin{aligned}Z_{in}&=Z_{out}^{*}\\&=\left\vert Z_{out}\right\vert e^{-j\Theta _{out}}\\&=\operatorname {Re} (Z_{out})-j\operatorname {Im} (Z_{out}).\\\end{aligned}}}
382:
274:
368:
to the signals impedance. Note this only maximizes the power transfer, not the efficiency of the circuit. When the power transfer is optimized the circuit only runs at 50% efficiency.
195:
812:
628:
235:
709:
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739:
263:
impedance at the source. The resulting equivalent circuit is purely resistive in nature, and there are no losses due to phase imbalance in the source or the load.
269:
892:
Signal reflections caused by an impedance mismatch at the end of a transmission line can result in distortion and potential damage to the driving circuitry.
85:
The circuit to the left of the central set of open circles models the source circuit, while the circuit to the right models the connected circuit.
1058:
74:
of impedance) is a measure of the load network's propensity to draw current. The source network is the portion of the network that transmits
51:
116:
Therefore, the input impedance of the load and the output impedance of the source determine how the source current and voltage change.
1011:
991:
749:
and the impedance of the load circuit have to be equal (or "matched"). If the impedance matches, the connection is known as a
1053:
996:"Aortic input impedance in normal man: relationship to pressure wave forms", JP Murgo, N Westerhof, JP Giolma, SA Altobelli
123:
circuit of the electrical network uses the concept of input impedance to determine the impedance of the equivalent circuit.
907:
will occur. This in turn can cause a reactive pulse of high voltage that can destroy the transmitter's final output stage.
899:
The standing waves created by the mismatch are periodic regions of higher than normal voltage. If this voltage exceeds the
241:
The input impedance of the driven stage (load) is much larger than the output impedance of the drive stage (source).
120:
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1002:
An excellent introduction to the importance of impedance and impedance matching can be found in
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341:{\displaystyle {\begin{aligned}Z_{in}&=X-j\operatorname {Im} (Z_{out})\\\end{aligned}}}
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256:
59:
921:
To maximise power transmission for radio frequency power systems the circuits should be
1023:
997:
961:
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on the transmission line. To minimize reflections, the characteristic impedance of the
742:
75:
835:, are designed to have an input impedance several orders of magnitude higher than the
1047:
904:
851:
133:
933:
741:, the load network will reflect back some of the source signal. This can create
17:
947:, which consists of an impedance matching device and the radiating element(s).
971:
832:
67:
881:
877:
78:, and the load network is the portion of the network that consumes power.
1029:
Interconnection of two audio units - Input impedance and output impedance
1033:
27:
Measure of the opposition to current flow by an external electrical load
1024:
Calculation of the damping factor and the damping of impedance bridging
915:
911:
910:
In RF systems, typical values for line and termination impedance are
870:
847:
or impedance-matching transformers are often used for these effects.
113:
the input terminals would be identical to the chosen load network.
753:, and the process of correcting an impedance mismatch is called
581:
When there is no reactive component this equation simplifies to
839:
of the source device connected to that input. This is called
986:, Winfield Hill, Paul Horowitz, Cambridge University Press,
940:(a balanced pair, a coaxial cable, or a waveguide), to the
850:
The input impedance for high-impedance amplifiers (such as
903:
strength of the insulating material of the line then an
768:
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681:
636:
587:
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272:
203:
154:
711:, does not match the impedance of the load network,
136:could be used to calculate the transfer function.
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655:
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570:
340:
229:
189:
1004:A practical introduction to electronic circuits
371:The formula for complex conjugate matched is
94:is the output impedance seen by the load, and
8:
66:to the electrical source network. The input
103:is the input impedance seen by the source.
1006:, M H Jones, Cambridge University Press,
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671:When the characteristic impedance of a
862:) is often specified as a resistance
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42:is the measure of the opposition to
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25:
190:{\displaystyle Z_{in}\gg Z_{out}}
807:{\displaystyle Z_{in}=Z_{line}}
1059:Audio amplifier specifications
623:{\displaystyle Z_{in}=Z_{out}}
558:
539:
524:
505:
331:
312:
230:{\displaystyle Z_{L}\gg Z_{S}}
1:
896:potentially corrupt signal.
888:Radio frequency power systems
1039:Input Impedance Measurement
1075:
630:as the imaginary part of
866:a capacitance (e.g., 2.2
704:{\displaystyle Z_{line}}
1034:Impedance and Reactance
856:field effect transistor
656:{\displaystyle Z_{out}}
984:The Art of Electronics
833:operational amplifiers
808:
735:
734:{\displaystyle Z_{in}}
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32:electrical engineering
1054:Electrical parameters
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140:Electrical efficiency
121:Thévenin's equivalent
84:
936:output, through the
901:dielectric breakdown
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831:, devices, such as
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841:impedance bridging
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756:impedance matching
751:matched connection
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667:Impedance matching
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338:
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40:electrical network
938:transmission line
924:complex conjugate
829:signal processing
823:Signal processing
747:transmission line
673:transmission line
364:complex conjugate
356:The condition of
16:(Redirected from
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957:Output impedance
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864:in parallel with
845:Voltage follower
837:output impedance
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928:throughout the
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962:Damping factor
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247:Power factor
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934:transmitter
932:, from the
930:power chain
127:Calculation
1048:Categories
978:References
972:Dummy load
827:In modern
72:reciprocal
68:admittance
58:), into a
52:resistance
882:mains hum
663:is zero.
537:
528:−
503:
473:Θ
466:−
422:∗
310:
301:−
255:carrying
215:≫
169:≫
134:Ohm's law
56:reactance
48:impedance
951:See also
253:circuits
64:external
942:antenna
926:matched
860:op-amps
366:matched
44:current
1010:
990:
945:system
875:
868:
251:In AC
38:of an
34:, the
257:power
76:power
70:(the
1008:ISBN
988:ISBN
916:75 Ω
914:and
912:50 Ω
197:(or
119:The
60:load
998:pdf
905:arc
884:).
873:∥ 1
30:In
1050::
918:.
878:pF
871:MΩ
854:,
675:,
534:Im
500:Re
307:Im
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791:l
787:Z
783:=
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