Gain control circuit and method of controlling gain

• US 8,045,059 B2
• Filed: 02/07/2007
• Issued: 10/25/2011
• Est. Priority Date: 02/08/2006
• Status: Expired due to Fees

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kwon, Jin-Ho
• Primary Examiner(s): NATNAEL, PAULOS M
• Application Number:
  US11/672,122
• Publication Number:
  US 20070182860A1
• Time in Patent Office: 1,721 Days
• Field of Search: 348/672, 348/678, 348/679, 348/687, 348/689, 348/663, 348/66, 348/668, 375/362, 386/112, 386/114
• US Class Current: 348/572
• CPC Class Codes: H04N 5/52 Automatic gain control
• CPC Class Codes: H04N 9/68 for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A gain control circuit includes an automatic gain controller (AGC), an analog-to-digital converter (ADC), a saturation field detecting block, a sync detector and a gain control block. The AGC controls amplitude of an analog image signal including a luminance signal, a color signal and a sync signal. The ADC converts the amplitude-controlled analog image signal to a digital image signal. The saturation field detecting block determines on a per field basis whether the digital image signal is saturated. The sync detector is configured to detect the sync signal in the digital image signal. The gain control block provides a gain control signal to the AGC based on an output signal of the saturation field detecting block and an output signal of the sync detector. Therefore, the gain control circuit may prevent saturation of the analog image signal by controlling gain of the analog image signal.

Claims

1. A gain control circuit comprising:

an automatic gain controller (AGC) configured to control amplitude of an analog image signal that includes a luminance signal, a color signal and a sync signal;

an analog-to-digital converter (ADC) configured to convert the amplitude-controlled analog image signal to a digital image signal;

a saturation field detecting block configured to determine on a per field basis whether the digital image signal is saturated;

a sync detector configured to detect the sync signal in the digital image signal; and

a gain control block configured to provide a gain control signal to the AGC based on an output signal of the saturation field detecting block and an output signal of the sync detector, wherein the saturation field detecting block comprises;

a saturation pixel counting block configured to count saturated pixels per scan line;

a saturation line decision block configured to determine whether each scan line is saturated based on the number of saturated pixels that is counted per scan lines;

a saturation line counting block configured to count the number of saturated scan lines per field; and

a saturation field decision block configured to determine whether each field is saturated based on the number of saturated scan lines that is counted per field.

2. The gain control circuit of claim 1, further comprising:

a direct current (DC) clamp that fixes a DC component of the analog image signal; and

a low-pass filter (LPF) that filters out the color signal and passes the luminance signal and the sync signal in the digital image signal.

3. The gain control circuit of claim 1, wherein the saturation pixel counting block determines that a pixel is a saturated pixel when a digital code of the pixel exceeds a first reference value.

4. The gain control circuit of claim 3, wherein the first reference value is set to a value ranging from about 80% to about 90% of a maximum digital code of the pixel.

5. The gain control circuit of claim 1, wherein the saturation line decision block determines that a scan line is a saturated scan line when total number of saturated pixels in the scan line exceeds a second reference value.

6. The gain control circuit of claim 5, wherein the second reference value is set to a value ranging from about 25% to about 30% of a number of pixels constituting one scan line.

7. The gain control circuit of claim 1 wherein the saturation field decision block determines that a field is a saturated field when a total number of saturated scan lines in the field exceeds a third reference value.

8. The gain control circuit of claim 7, wherein the third reference value is set to a value ranging from about 25% to about 30% of a total number of the scan lines constituting one field.

9. The gain control circuit of claim 1, wherein the gain control block provides the gain control signal for reducing the amplitude of the analog image signal to the AGC when the saturation field is detected and provides the gain control signal for controlling the amplitude of the analog image signal based on the output signal of the sync detector to the AGC when a saturation field is not detected.

10. A method of controlling gain comprising:

controlling amplitude of an analog image signal that includes a luminance signal, a color signal, and a sync signal;

converting the amplitude-controlled analog image signal to a digital image signal;

determining on a per field basis whether the digital image signal is saturated;

detecting the sync signal in the digital image signal; and

providing a gain control signal that controls the amplitude of the analog image signal based on the detected sync signal and the saturated field that is determined, wherein determining on a per field basis whether the digital image signal is saturated comprises;

counting the number of saturated pixels per scan line;

determining whether each scan line is saturated based on the number of saturated pixels that is counted per scan line;

counting the number of saturated scan lines per field; and

determining whether each field is saturated based on the number of saturated scan lines that is counted per field.

11. The method of claim 10, further comprising:

fixing a DC component of the analog image signal; and

filtering out the color signal and passing the luminance signal and the sync signal in the digital image signal.

12. The method of claim 10, wherein counting the number of the saturated pixels comprises:

receiving the digital image signal including the luminance signal and the sync signal;

determining that a pixel is a saturated pixel when a digital code of the pixel exceeds a first reference value; and

counting per scan line the number of saturated pixels having the digital code exceeding the first reference value.

13. The method of claim 12, wherein the first reference value is set to a value ranging from about 80% to about 90% of a maximum digital code of the pixel.

14. The method of claim 13, wherein the number of saturated pixels increases by one whenever the digital code of the pixels exceeds the first reference value.

15. The method of claim 10, wherein determining whether each scan line is saturated comprises:

receiving the number of saturated pixels that is counted;

comparing the number of saturated pixels with a second reference value; and

determining that a scan line is a saturated scan line when a total number of saturated pixels in the scan line exceeds the second reference value.

16. The method of claim 15, wherein the second reference value is set to a value ranging from about 25% to about 30% of a number of pixels constituting one scan line.

17. The method of claim 16, wherein the number of saturated scan lines increases by one, whenever the number of saturated pixels in one scan line exceeds the second reference value.

18. The method of claim 10, wherein determining whether each field is saturated comprises:

receiving the number of saturated scan lines in one field;

comparing the number of saturated scan lines with a third reference value; and

determining a field as a saturated field when a total number of saturated scan lines in the field exceeds the third reference value.

19. The method of claim 18, wherein the third reference value is set to a value ranging from about 25% to about 30% of a total number of the scan lines constituting one field.

20. The method of claim 19, wherein the third reference value corresponds to 80 in case of the NTSC interlaced scan method and corresponds to 160 in case of the progressive scan method.

21. The method of claim 10, wherein the amplitude of the analog image signal is controlled based on the detected sync signal when the saturated field is not detected.

22. The method of claim 10, wherein the amplitude of the analog image signal is reduced when the saturated field is detected.