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NOT 454-2002-en

AMPLIFICATION TYPES

Description: 

Large TV distribution networks need amplifiers that meet the more stringent requirements of the CATV designers.

One of the most important problems that the installer faces when installing a TV distribution network is the distortion.

These amplifiers must incorporate circuits that are capable to give outstanding low distortion and broad bandwidths.

Single-ended transistor configurations for final amplification stages are not suitable for these applications, because this sort of amplification produces many second harmonics of all the carried channels.

To overcome these distortions, manufacturers of amplifiers use cascode push-pull circuits.

Cascode configurations in combination with the right transistors, working with the optimised emitter current, significantly reduce distortion by eliminating collector non-linearity.

They also have the advantage of low noise transistors combining high gain in the first stage with low emitter resistance and high shunt resistance.

On the other hand a push-pull reduces distortion even further by halving the high frequency emitter current in each half of the circuits and reduces second order beat by cancellation of the second order products of the output signals.

Finally, there is the power doubler configuration.

It is a configuration based on two standard push-pull modules connected in parallel.

Theoretically, this option doubles the output power without any increase of distortion.

However ,in practice, because of the losses introduced by the 75 ohms matching considerations, the output level might not reach the expected theoretical output level.

Id Anrterior: 
9
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