Adaptive multiple conversion ramp analog-to-digital converter

Active Publication Date: 2014-08-14
OMNIVISION TECH INC
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

Many image sensors have an image quality that is limited by a number of factors.
For example, temporal noise (including various readout noises and quantization noise) can significantly limit the image quality of an image sensor application.
However, this is typicall

Method used

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  • Adaptive multiple conversion ramp analog-to-digital converter
  • Adaptive multiple conversion ramp analog-to-digital converter
  • Adaptive multiple conversion ramp analog-to-digital converter

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Embodiment Construction

[0014]In the following description, numerous specific details are set forth, such as, for example, specific readout circuits, voltage ramp signals, calibration circuits orders of operations, etc. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

[0015]FIG. 1 is a block diagram illustrating image sensor 100 having multiple adaptive ADCs 118, in accordance with an embodiment of the present disclosure. Image sensor 100 includes pixel array 110, control circuitry 120, readout circuitry 130, and optional digital processing logic 150. For simplicity of illustration, the illustrated embodiment of pixel array 110 only shows two columns 112, each having four pixel cells 114. However, it is to be appreciated that actual image sensors commonly include from hundreds to thousands of columns, and ea...

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Abstract

An example ramp analog-to-digital converter (ADC) for generating at least one bit of a digital signal includes a modified ramp signal generator, a comparator, and a control circuit. The modified ramp signal generator receives a ramp signal and generates a modified ramp signal in response thereto. The comparator compares an analog input with the modified ramp signal. The control circuit controls the modified ramp signal generator, such that the analog input is converted a variable M number of times for each period of the ramp signal. The number M is dependent on a magnitude of the analog input. In one example, the number M is greater for analog inputs of a lower magnitude, such that the analog inputs of the lower magnitude are converted more times than analog inputs of a higher magnitude.

Description

BACKGROUND[0001]1. Field of the Invention[0002]This disclosure relates generally to ramp analog-to-digital converters, and in particular, but not exclusively, those used in the readout circuitry of a complementary metal-oxide-semiconductor (CMOS) image sensor.[0003]2. Background Information[0004]Image sensors are ubiquitous. They are widely used in digital still cameras, digital video cameras, cellular phones, security cameras, medical devices, automobiles, and other applications.[0005]Many image sensors have an image quality that is limited by a number of factors. One example such factor is temporal noise. For example, temporal noise (including various readout noises and quantization noise) can significantly limit the image quality of an image sensor application. Various methods can be implemented to reduce noise. One example for reducing temporal noise is to enlarge the physical device area on the substrate. However, this is typically not feasible given the layout and size constra...

Claims

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Application Information

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IPC IPC(8): H03M1/00
CPCH03M1/56H03M1/007H04N5/335H03M1/0697H03M1/123H03M1/20H04N25/00
Inventor YANG, ZHENG
Owner OMNIVISION TECH INC
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