System for non linearity correction by intermediate frequency premodulation in television equipment
AssigneeL.G.T. Laboratoire General des Telecommunications
InventorClaude Cluniat
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Abstract
In equipment for transmitting or re-transmitting television signals comprising, in the intermediate frequency stage, group propagation time correction cells for linearizing the phase-frequency characteristic of the equipment, the non linearity correction system of the invention uses these cells while completing them with an amplitude pre-modulation control circuit and/or a frequency premodulation control circuit, for correcting amplitude and phase non linearities affecting the pole carrier frequencies of the correction cells.
Claims9
A system for pre-correcting, by intermediate frequency pre-modulation, non-linearities introduced into a high frequency amplified television signal in common channel transmission equipment having intermediate frequency stages, comprising at least one group delay time correction cell receiving said signal and having an output and placed in said intermediate frequency stages, including:
- a direct channel receiving said signal and having an output;
- a compensated channel receiving said signal and having an output which when added to said direct channel output comprises said cell output, including:
- an amplifier receiving said signal;
- and
- a group delay time modulation circuit, connected to said amplifier, for introducing group delay time corrections to said signal at a frequency of a correction pole, said delay time modulation circuit having a group delay time control input and including an oscillating circuit for tuning said delay time modulation circuit to said correction pole frequency, said delay time modulation circuit having no effect on an amplitude of said signal at said correction pole frequency;
- and
- an amplitude pre-modulation control circuit, having a control input and an output which is connected to said amplifier, for introducing amplitude corrections of said signal at said correction pole frequency in a manner independent of said group delay time corrections.
Dependencies are inferred from the claim text.