US 5,847,701 A · Method and apparatus implemented in a computer system for determining the frequency used by a graphics source for generating an analog display signal

Abstract

A display unit which can determine the frequency (original frequency) used by a graphics source for generating an analog signal. A sequence of test patterns are generated according to a predetermined convention. The sequence of test patterns are encoded in an analog display signal in a graphics source and transmitted to a digital display unit. The digital display unit samples the analog display signal to generate a sequence of sampled values. The digital display unit determines whether the sampled values equal one of the sequence of test patterns based on the predetermined convention. The digital display unit varies (changes) the sampling frequency until the sampled values equal one of the sequence of test patterns. The sampling frequency equals the original frequency when the sampled values equal the sequence of test patterns. In one embodiment, zeros and ones are used in alternate positions of each horizontal line. The absence of runs in the sampled values indicates that the sampling frequency equals the original frequency.

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Claims31

Dependent claims

In a computer system including a digital display unit which receives analog display signals generated by a graphics source and displays images encoded in the received analog display signals, wherein said graphics source generates said analog display signals from pixel data elements, said graphics source generating said analog display signals using an original frequency, a method of enabling said digital display unit to determine said original frequency, said method comprising the steps of:

(a) generating a sequence of test patterns according to a predetermined convention;
(b) encoding said sequence of test patterns in an analog display signal using said original frequency, said step of encoding being performed in said graphics source;
(c) sending said analog display signal encoded with said sequence of test patterns from said graphics source to said display unit;
(d) receiving in said display unit said analog display signal sent in step (c);
(e) sampling a portion of said received analog display signal using a sampling clock having a sampling frequency to generate a plurality of sampled values;
(f) determining whether said plurality of sampled values are equal to at least one of said sequence of test patterns based on said predetermined convention;
and
(g) changing the sampling frequency and performing steps (e) and (f) until said plurality of sampled values for a portion of said analog display signal are equal to one of said sequence of test patterns encoded in said analog display signal,
wherein said original frequency equals said sampling frequency when said plurality of sampled values are equal to one of said sequence of test patterns.

6 more elements

A frequency measurement circuit for use in a digital display unit of a computer system, said digital display unit receiving analog display signals generated by a graphics source and displaying images encoded in the received analog display signals, wherein said graphics source generates said analog display signals from pixel data elements, said graphics source generating said analog display signals using an original frequency, said frequency measurement circuit determining said original frequency, said frequency measurement circuit comprising:

a clock generator for generating a sampling clock having a sampling frequency;
an analog to digital converter (ADC) coupled to said clock generator, said ADC receiving an analog display signal from said graphics source, wherein said analog display signal comprises display data or a sequence of test patterns, said sequence of test patterns being generated by said graphics source according to a predetermined convention, said ADC sampling said received analog display signal at said sampling frequency to generate a plurality of sampled values;
a sampling error measurement block for determining whether said plurality of sampled values are equal to one of said sequence of test patterns based on said predetermined convention;
and
a micro-controller coupled to said clock generator, said micro-controller controlling said clock generator to change the sampling frequency, wherein said ADC samples said analog display signal using changed sampling frequency, said micro-controller micro-controller changing said sampling frequency until said sampling error measurement block determines that said plurality of sampled values generated with a changed sampling frequency equal one of said sequence of test patterns according to said predetermined convention,
wherein said original frequency equals said sampling frequency when said plurality of sampled values are equal to said sequence of test patterns.

3 more elements

A computer system comprising:

a graphics source for generating an analog display signal including a plurality of frames, some of said plurality of frames encoding display data, wherein display data of a frame represents an image, said graphics source encoding a sequence of test patterns generated according to a predetermined convention in some of said plurality of frames, said graphics source generating said plurality of frames at an original frequency;
and
a digital display unit for receiving said analog display signal, said digital display unit including a display screen for displaying said images encoded in said plurality of frames,
said digital display unit sampling said analog display signal to generate display signals to display said images on said display screen,
said digital display unit determining said original frequency by examining said some of said plurality of test frames including said sequence of test patterns,
wherein said digital display unit samples any of subsequently received frames comprised in said plurality of frames at a sampling frequency equal to said original frequency.

3 more elements

Dependencies are inferred from the claim text.

Description10,815 words

Summary1,886 words

#The present application is related to the following co-pending Patent Applications, which are both incorporated in their entirety into the present application herewith:

#1. Patent Application entitled, "A Method and Apparatus for Upscaling an Image", Filed Feb. 24, 1997, having Ser. No. 08/804,623 and Attorney Docket Number: PRDN-0001;

#2. Patent Application entitled, "A Method and Apparatus for Clock Recovery in a Digital Display Unit", Filed Feb. 24, 1997, having Ser. No. 08/803,824 and Attorney Docket Number: PRDN-0002; and

Brief description of the drawings12 figures

#The present invention will be described with reference to the accompanying drawings, wherein:

#FIG. 1A is a block diagram of an analog to digital converter (ADC) and a digital to analog converter (DAC) connected by an analog link illustrating a typical scenario in which analog display signals generated by DAC are transmitted to ADC;

#FIG. 1B is a diagram illustrating the need for the sampling frequency to be equal to the frequency used by DAC (original frequency) to generate the analog display signals;

Detailed description8,623 words

#In accordance with the present invention, a graphics source encodes a sequence of test patterns (test data) according to a predetermined convention. The graphics source encodes the test pattern at an original frequency in an analog display signal. The analog signal is then transferred to a display unit. The display unit samples the analog signal at a sampling frequency. The display unit varies the sampling frequency until the sampled values equal a test pattern. When the samples values equal the test pattern, the original frequency equals the sampling frequency at the time of sampling.

#Each test pattern can be encoded into a portion of a frame (e.g., in a horizontal line) or can span multiple frames according to a predetermined convention. Both the graphics source and the digital display need to operate according to the convention. Several test patterns are generally transferred to provide sufficient time for the display unit to adaptively determine the original frequency.

#One or more embodiments of the present invention will be described in further detail below. Before describing the invention in great detail, it is useful to describe an example environment in which the invention can be implemented. The details of making and using the invention will be clear from the description.

Facts

Application

08/872,774Filed 10 Jun 1997

Granted

8 Dec 1998

Term ended

10 Jun 2017

Estimated · how

20 years from earliest known nonprovisional domestic filing. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination. Patent term adjustment is unavailable; no adjustment was added.

Classification4 codes

G09G 5/006
Details of a display terminal, the details relating to the control arrangement of the display terminal and to the interfaces thereto: details of…
G09G 5/18
Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators: timing circuits for…
G09G 2370/04
Aspects of data communication: exchange of auxiliary data, i.e. other than image data, between monitor and graphics controller
G09G
Arrangements or circuits for control of indicating devices using static means to

Method and apparatus implemented in a computer system for determining the frequency used by a graphics source for generating an analog display signal

Life of this patent

Method and apparatus implemented in a computer system for determining the frequency used by a graphics source for generating an analog display signal

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims31

Description10,815 words

Drawings

Classification4 codes

Life of this patent

Description10,815 words