Circuit for changeable prolongation of the running time of an ul

Details Circuit for changeable prolongation of the running time of an ul Circuit for changeable prolongation of the running time of an ul

1985-07-18

1987-07-07

Groody, James J.

Facsimile and static presentation processing

Static presentation processing

Attribute control

358 23, 307262, H04N 966

Patent

active

046790640

DESCRIPTION:

BRIEF SUMMARY
STATE OF THE ART

The invention is based on a circuit for an adjustable prolongation of a (phase-) running time of an ultrasound delay line having a delay of somewhat less than a line duration of color TV signal in the range of the color carrier frequency.
Price efficient ultrasound delay lines as used, for example, in the PAL-running time-decoder for signal dividing in color television receivers, delay the supplied signal by one line period .tau..sub.H by 1/4 of a color carrier period (64 us-56 ns). If such ultrasound delay lines should be used also for circuits, wherein one delay duration of exactly one line duration .tau..sub.H is required (for example, comb filter, signal drop out-compensator), then passive delay members for prolonging the running time could be used. However, this is very expensive.
It is therefore an object of the invention to provide a circuit of the aforementioned type with which a delay duration of exactly one line duration is obtainable without additional delay members.


ADVANTAGES OF THE INVENTION

The circuit in accordance with the invention with the characterizing features of the main claim has the advantage that price efficient ultrasound delay lines may be used without any great additional effort for generating a delay time of exactly one line duration.
Advantageous further embodiments and improvements of the circuit stated in the main claim are possible by the measures stated in the subclaims. It is particularly advantageous that an automatic phase adjustment is possible when a phase detector and, for exaample, a capacity-variation diode.


DRAWING

Exemplified embodiments of the invention are illustrated and are explained in detail in the following description. The drawings show:
FIG. 1 A circuit in accordance with the invention,
FIG. 1a a vector diagram of the signal phases occuring in FIG. 1
FIG. 2 A circuit in accordance with the invention with phase readjustment
In the circuit illustrated in FIG. 1, a television signal with an input phase .phi..sub.0 (see also FIG. 1a) to be delayed in the color carrier frequency is applied on terminal 1. After transmission through a transistor impedance converter stage 2,3 this signal is applied to output 4. A phase rotating circuit which consists of a changeable resistor 6, a changeable capacitor 7 as well as a centrally tapped transformer 8 with a first winding 8' is connected to the output 4 and a second winding 8". The connecting point 9 between resistor 6 and the transformer 8 is connected with the first input 10 of an ultrasound delay line 11, whose second input 12 is applied on the reference potential. This ultrasound delay line 11 represents a delay line for the signal dividing with a delay time of .tau.=63,944 us-56 ns) as customary in PAL-running time-decoders.
The phase rotating circuit effects with .vertline.X.sub.C .vertline.=R in the color carrier frequency a rotating of the input phase .phi..sub.0 by the RC-combination 6/7 by -45.degree. (vector A) and by the CR-combination 7/6 by +45.degree. (vector B). Due to the inverting characteristic of the center tapped transformer 8, the vector B appears as being rotated at point 9 by 180.degree. (vector B'), so that a resulting vector Z is obtained at the input of the ultrasound delay line 11. This vector Z is phase rotated by .phi..sub.0 by .DELTA..phi.=90.degree. with respect to the input phase angle of the vector which angle corresponds to a quarter of a color carrier period or 56 ns. Thus, the phase or running time of the signal to be picked off at the output 13 of the ultrasound delay line 11 corresponds exactly one line duration (.tau.=64 us.) By adjusting the resistor 6 or the capacitor 7 the phase shift can be adjusted. Instead of the passive phase determining elements 6 and 7, voltage controlled elements may be used, for example, instead of resistor 6 a field effect transistor, or, instead of the capacitor 7 a capacity variation diode, whereby the total running time can be maintained constant in an automatic control circuit.
FIG. 2 illustrates such an automatic control

REFERENCES:
patent: 3433780 (1969-03-01), Swaluw
patent: 3446913 (1969-05-01), Scholz
patent: 3745239 (1973-07-01), Renaud
"Demodulation Circuits for PAL Colour T.V. Receivers", Bruch, Electronic Engineering, Aug. 64, pp. 512-518, 606-611.

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