JPH033489A - Television broadcast equipment - Google Patents

Abstract

PURPOSE:To always keep both a pedestal level and a synchronizing signal level constant by returning part of an output signal of a broadcast equipment to a synchronizing separation reformation circuit of a video signal. CONSTITUTION:An output of a synchronizing signal expander 5 is amplitude- modulated by an amplitude modulator 6, passes through a pedestal AGC circuit 8, is converted into a transmission frequency by a frequency converter 9 and amplified to a required output by a power amplifier 11. Then part of the output of the power amplifier 11 is fed back to the pedestal AGC circuit 8 and a synchronizing signal reforming circuit 3. Part of the output of a transmitter is fed back to the synchronizing signal reforming circuit 3 in addition to the pedestal AGC circuit 8 to keep the pedestal level constant in this way. Thus, the pedestal level and the level of the synchronizing signal are kept constant even to fluctuation of white and black levels.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a compensation circuit for a television broadcaster.

[Prior Art] Conventionally, this type of television broadcasting machine has had a function of keeping the pedestal level constant by applying feedback to the pedestal AGC circuit 8, as shown in FIG.

In the conventional television broadcasting machine described above, the pedestal level is kept constant, but in a solid-state broadcasting machine in which class AB operation transistors are connected in cascade, the part of the synchronization signal whose amplitude is higher than the pedestal level is kept constant. However, it has the disadvantage that the length changes due to changes in operating current due to changes in image components.

[Problems to be Solved by the Invention] An object of the present invention is to provide a television broadcasting device that can always keep both the pedestal level and the synchronization signal level constant.

[Means and effects for solving the problem] The television broadcasting device of the present invention extracts a part of the broadcasting device output signal and returns it to the synchronization separation and regeneration circuit (3) in response to a change in the synchronization signal due to a change in the image. This makes it possible to keep the length of the synchronization signal constant not only in the conventional pedestal AGC circuit (8) but also in response to changes in the operating current of class AB operation power amplifiers.

[Example] Next, the present invention will be described with reference to the drawings. FIG. 1 is a system diagram showing one embodiment of the present invention. The input video signal input from the video signal input terminal l is separated by the synchronization separation circuit 2 into an image component and a synchronization signal part of the video signal. The synchronizing signal portion is expanded to the required length by the synchronizing circuit 3. Further, the expanded synchronization signal is combined with the image component by a synthesizer 4 and outputted as an output of a synchronization signal expander 5.

The output of the synchronizing signal expander 5 is subjected to amplitude modulation by the amplitude modulator 6, and then passes through the pedestal AGC circuit 8 to the output signal 5.
It is converted to a transmission frequency by a frequency converter 9, and amplified to a required output by a power amplifier @11. A part of the output of the power amplifier 11 is supplied to the pedestal AGC circuit 8.
and is fed back to the synchronous circuit 3.

That is, even when the image components change drastically, such as a black-and-white change, and the linearity changes due to a change in the operating current of the class AB power amplifier, and not only the pedestal level but also the length of the synchronization signal changes, Gain control is performed independently on the pedestal level and synchronization signal by feedback, making it possible to maintain the level.

[Effects of the Invention] As explained above, in the present invention, in addition to the pedestal AGC circuit (8) for keeping the pedestal level constant,
A part of the transmitter output is fed back to the synchronous circuit (3). This has the effect of keeping the pedestal level and the synchronization signal level constant even when black and white fluctuations occur.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of a television broadcasting machine according to the present invention, and FIG. 2 is a system diagram of an example of a conventional television broadcasting machine. 1...Video signal input terminal 2... - Synchronous separation circuit 3...Synchronizable circuit 4...Composition circuit 5...Synchronization signal expander 6...Amplitude modulator 8...Pedestal AGC circuit 9...Frequency converter 10...・Local oscillator 11--Power amplifier

Claims (1)

[Claims] In a television broadcasting device having a video signal synchronous separation and regeneration circuit, an amplitude modulator, a pedestal AGC circuit, a frequency conversion circuit, and a power amplifier, a part of the output signal of the broadcasting device is converted into a video signal synchronous separation and regeneration circuit. A television broadcasting device characterized by returning to a component circuit.