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Distributed amplifier: Difference between revisions
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Thus, it is possible to construct an amplifier with a gain of 100 and a risetime | Thus, it is possible to construct an amplifier with a gain of 100 and a risetime | ||
of 3ns by using ten instances of Amplifier 1 connected to form a distributed amplifier. | of 3ns by using ten instances of Amplifier 1 connected to form a distributed amplifier. | ||
The key difference between a distributed amplifier and a conventional amplifier | |||
composed of cascaded stages is that in a distributed amplifier, the input of | |||
each stage is the original signal, not the output of a previous stage. This | |||
eliminates the cumulative degradation of the risetime that occurs in conventional | |||
cascaded stages. | |||
One of the most important challenges when building distributed amplifiers is | |||
to avoid reflections in the signal path. For example, when the input signal | |||
reaches the input of one stage, it is important to avoid having the parasitic capacitance | |||
of that stage cause an impedance discontinuity in the signal path, which would cause | |||
reflection. Since eliminating the parasitic capacitance is not possible, | |||
the approach is usually to reduce the capacitance of the transmission line in | |||
the region of an amplifier so that the amplifier's parasitic capacitance can | |||
substitute for the capacitance of that region of the | |||
transmission line, this avoiding impedance discontinuities. The design of | |||
distributed amplifiers is closely related to the design of synthetic delay lines | |||
made from L-C sections. This, in turn, is based on the notion that a transmission | |||
line can be modeled as a series of L-C sections. | |||