Prior art

Analysis of Prior Art for U.S. Patent 7,557,788: Gamma Reference Voltage Generator

Washington D.C. – April 26, 2026 – A detailed analysis of the prior art cited in U.S. Patent 7,557,788, titled "Gamma reference voltage generator," reveals a landscape of existing technologies aimed at calibrating and controlling gamma correction in liquid crystal displays (LCDs). The patent, granted on July 7, 2009, to inventors Richard V. Orlando and Trevor A. Blyth, addresses the need for a programmable and non-volatile solution to compensate for panel-to-panel manufacturing variations. This report outlines the most relevant prior art and its potential impact on the claims of the '788 patent.

The core of the '788 patent lies in its method for calibrating an LCD by providing it with electrically reprogrammable and non-volatile gamma reference control. This process involves testing the display with an external optical sensor, varying the gamma reference voltage levels, optimizing these levels with an external control circuit and algorithm, and finally storing the optimized values in the non-volatile gamma reference control.

An examination of the prior art cited by the patent examiner indicates that while the concept of gamma correction was well-established, the specific combination of features claimed in the '788 patent, particularly the use of external calibration with non-volatile analog memory, was considered novel.

Key Prior Art and Potential Anticipation:

Below is a review of the primary prior art references cited against U.S. Patent 7,557,788 and an analysis of which claims they could potentially anticipate under 35 U.S.C. § 102.

1. U.S. Patent 6,593,934: "Automatic gamma correction system for displays"

• Full Citation: US Patent 6,593,934 B1
• Publication Date: July 15, 2003
• Filing Date: November 16, 2000
• Brief Description: This patent discloses an automatic gamma correction system that uses a light-sensing device to measure the brightness of a display. The system then adjusts the gamma values in a lookup table to match a desired gamma curve. The adjusted values are stored in a memory.
• Potential Anticipation of Claims: This reference appears to be the most significant prior art. It discloses several key elements of the '788 patent's claims, including testing a display with an optical sensor (claim 1b, 5a), varying gamma reference voltage levels (claim 1c, 5b), and optimizing those levels (claim 1d, 5c). However, the '934 patent primarily focuses on a digital approach using a lookup table stored in a memory that may not be explicitly non-volatile in the same manner as the analog floating gate memory cells described in the '788 patent. The distinction between digital lookup tables and the directly programmable, non-volatile analog voltage storage is a key differentiator for the '788 patent. Therefore, while it teaches the general concept of external optical feedback for gamma correction, it may not fully anticipate the "electrically reprogrammable and non-volatile" gamma reference control capability as claimed.

2. U.S. Patent 6,373,478: "Liquid crystal display driver supporting a large number of gray-scale values"

• Full Citation: US Patent 6,373,478 B1
• Publication Date: April 16, 2002
• Filing Date: March 26, 1999
• Brief Description: This patent describes an LCD driver that can generate a large number of gray-scale voltages. It includes a gamma correction circuit that can be adjusted. The focus is on the driver architecture to achieve a high number of gray levels.
• Potential Anticipation of Claims: The '478 patent discusses adjustable gamma correction but does not explicitly describe a method of calibrating the display using an external optical sensor and storing the optimized values in a non-volatile manner to compensate for manufacturing variations. Its primary contribution is the driver circuit design. Therefore, it is unlikely to anticipate the core method claims (1, 3, and 5) of the '788 patent, which are centered on the calibration process with external feedback and non-volatile storage.

3. U.S. Patent 5,754,150: "Liquid crystal luminance adjusting apparatus"

• Full Citation: US Patent 5,754,150 A
• Publication Date: May 19, 1998
• Filing Date: February 17, 1995
• Brief Description: This patent details an apparatus for adjusting the luminance of a liquid crystal display. It includes a mechanism for setting the gamma characteristic of the display.
• Potential Anticipation of Claims: The '150 patent, being an earlier reference, describes methods for adjusting display luminance and gamma characteristics. However, it does not appear to disclose the combination of an external optical sensor for feedback-based calibration and the use of electrically reprogrammable, non-volatile memory to store the resulting gamma correction values for individual panel compensation. Its teachings are more general to the adjustment of display parameters.

4. U.S. Patent 7,233,305: "Gamma reference voltage generator"

• Full Citation: US Patent 7,233,305 B1
• Publication Date: June 19, 2007
• Filing Date: December 23, 2003
• Brief Description: This patent is a parent to the '788 patent and shares the same inventors. It describes a programmable buffer integrated circuit with non-volatile storage for gamma correction voltages.
• Potential Anticipation of Claims: As this is a parent application from which the '788 patent claims priority, it does not constitute prior art under 35 U.S.C. § 102. The '788 patent is a continuation, which typically involves claims to a different aspect of the invention disclosed in the parent application. The disclosure of the '305 patent provides the foundational description of the programmable gamma reference generator hardware that is utilized in the calibration methods claimed by the '788 patent.

In conclusion, while the prior art establishes the general principles of gamma correction and the use of feedback for display calibration, the claims of U.S. Patent 7,557,788 are distinguished by their specific combination of using an external optical sensor, an external control circuit and algorithm for optimization, and, crucially, storing the optimized analog gamma reference voltages in an electrically reprogrammable and non-volatile memory integrated with the display. This allows for a streamlined, automated, and permanent calibration process to address manufacturing variability on a per-panel basis. The '934 patent comes closest to anticipating the claims but its focus on a digital lookup table approach likely provides a sufficient distinction to support the novelty of the '788 patent's claims.