Solid State Imaging Ramp Signal Slope Control
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Solution Overview
Problem
Existing solid-state imaging apparatuses with AD converting circuits using multiple ramp signals face accuracy issues due to individual and relative accuracy errors, and increasing AD conversion gain can lead to line noise, especially when the slope of the ramp signal is reduced.
Innovation Solution
A solid-state imaging apparatus with a comparator, counter circuit, and slope converting circuit, where capacitors are used to adjust the slope of the ramp signal, allowing for variable AD conversion gain without introducing line noise, by storing count values and performing capacitance division to control the ramp signal's slope.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the slope of the ramp signal is reduced to increase AD conversion gain, then AD conversion gain is improved, but line noise appears in each pixel row
Solution Approach 1:
The patent divides the ramp signal generation into two independent parts: a common-mode ramp signal generated by a ramp signal source, and a differential ramp signal generated by the slope converting circuit using capacitors. This segmentation allows the common-mode noise to be rejected while the differential signal provides the desired slope adjustment for gain control without introducing line noise.
Solution Approach 2:
Instead of directly adjusting the ramp signal slope at the source (which amplifies noise), the patent inverts the approach by generating a complementary ramp signal through the slope converting circuit. The differential operation between the original and converted signals achieves slope adjustment while the common-mode noise component is naturally suppressed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces line noise and maintains high AD conversion accuracy even when changing the AD conversion gain, by properly controlling the slope of the ramp signal, thus improving the overall performance of the imaging apparatus.
Implementation Method 1
an slope converting circuit including a first capacitor connected between an output terminal of the reference signal generating circuit and the second input terminal of the comparator, and a second capacitor connected between the second input terminal of the comparator and a reference voltage
Data Source
AI summary
A solid-state imaging apparatus comprises a plurality of matrix pixels, a reference signal generator for generating a ramp signal, a counter for performing counting according to the ramp signal output, and an AD converter, arranged for each pixel column, for performing AD conversion by comparing a pixel signal from the pixel with the ramp signal. Further, the AD converter includes a comparator to which the pixel signal and the reference signal are input, a storage for storing the AD conversion result, and an slope converter, between the output terminal of the reference signal generator and the input terminal of the comparator, for changing a gradient of the ramp signal, so that the noise overlaid on the ramp signal changes depending on the gradient of the ramp signal. Thus, it is possible to prevent generation of a horizontal-line noise in the ramp signal.