Television receiver including a teletext decorder

• US 4,912,555 A
• Filed: 01/10/1989
• Issued: 03/27/1990
• Est. Priority Date: 01/11/1988
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Van Gestel, Henricus
• Primary Examiner(s): Shepperd, John W.
• Assistant Examiner(s): Parker, Michael D.
• Application Number:
  US07/295,713
• Time in Patent Office: 441 Days
• Field of Search: 358/141, 358/142, 358/146, 358/147, 358/183, 340/723, 340/748, 340/750, 340/799, 340/800
• US Class Current: 348/468
• CPC Class Codes: G09G 5/24 Generation of individual character patterns

Abstract

In a teletext decoder circuit the character generator supplies picture elements at a rate of nominally approximately 6 MHz under the control of display pulses occurring at the same rate. These display pulses are derived from reference clock pulses which occur at a rate which is not a rational multiple of 6 MHz. The character generator comprises a generator circuit which receives the reference clock pulses and selects, from each series of N reference clock pulses, as many pulses as correspond to the number of horizontal picture elements constituting a character, while the time interval of N reference clock pulses corresponds to the desired width of the characters to be displayed. The character generator supplies picture elements of distinct length, while the length of a picture element is dependent on the ordinal number of this picture element in the character.

Claims

1. A receiver for television signal s including a teletext decoder circuit for decoding teletext signals constituted by character codes which are transmitted in the television signal, and comprising:

a video input circuit receiving the television signal and converting it into a serial data flow;

an acquisition circuit for receiving the serial data flow supplied by the video input circuit and selecting that part therefrom which corresponds to the teletext page described by the viewer;

a character generator comprising;

a memory medium addressed by the character codes which together represent the teletext page desired by the user and which in response to each character code successively supply m₂ series of m₁ simultaneously occurring character picture element codes each indicating wether a corresponding picture element of the character must be displayed in the foreground colour or in the background colour;

a generator circuit receiving a series of reference clock pulses and deriving display clock pulses therefrom;

a converter circuit receiving each series of m₁ simultaneously occurring character picture element codes as well as the display clock pulses for supplying the m₁ character picture element codes of a series one after the other and at the display clock pulse rate;

a display control circuit receiving the serial character picture element codes and converting each into an R, a G and a B signal for the relevant picture element of the character to be displayed;

characterized in that

the generator circuit is adapted to partition the series of reference clock pulses applied thereto into groups of N reference clock pulses each, in which N reference clock pulse periods correspond to the desired width of a character to be displayed, and to select from each such group m₁ clock pulse to function as display clock pulses;

the converter circuit is adapted to supply each character picture element code during a period which is dependent on the ordinal number of the character picture element code in the series of m₁ character picture element codes.

2. A character generator for use in a receiver teletext claim 1, comprising:

a memory medium which is addressable by character codes and successively applies m₂ series of m₁ simultaneously occurring character picture element codes in response to a character code applied as an address thereto, each character picture element code indicating whether a corresponding picture element of the character must be displayed in the foreground colour or in the background colour;

a generator circuit receiving a series of reference clock pulses and deriving display clock pulses therefrom;

a converter circuit receiving each series of m₁ simultaneously occurring character picture element codes and the display clock pulses for supplying the m₁ character picture element codes of the series one after the other at the display clock pulse rate;

a display control circuit receiving the serial character picture element codes and converting each into an R, a G and a B signal for the relevant picture element of the character to be displayed;

characterized in that

the generator circuit is adapted to partition the series of reference clock pulses applied thereto into groups of N reference clock pulses each, in which N reference clock pulse periods correspond to the desired width of a character to be displayed, and to select from each such group m₁ clock pulses to function as display clock pulses;

the converter circuit is adapted to supply each character picture element code during a period which is dependent on the ordinal number of the character picture element code in the series of m₁ character picture element codes.