Cyclic ADC Noise Cancellation With Shared Gain-Stage Capacitors
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Solution Overview
Problem
Cyclic analog/digital converters integrated in CMOS image sensors lack amplification functionality, leading to increased circuit complexity and size when noise-canceling circuits with amplification are integrated, and existing solutions require complex timing and processing steps for noise cancellation.
Innovation Solution
A cyclic A/D converter design that shares plural capacitors and an operational amplifier for both noise cancellation and cyclic A/D conversion, using a gain stage with first, second, and third capacitors and an operational amplifier circuit to generate a difference signal, and a sub A/D converter circuit, logic circuit, D/A converter circuit, and timing circuit to control operations, allowing for amplification and noise cancellation in a single circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If noise-canceling circuits with amplification are integrated in a column, then low-noise readout is achieved, but circuit scale increases
Solution Approach 1:
The patent combines the noise-canceling circuit with amplification function and the cyclic A/D converter into a single integrated circuit. The operational amplifier and capacitors are shared between the noise cancellation process and the cyclic A/D conversion process, eliminating the need for separate circuits and reducing overall circuit scale while maintaining low-noise readout capability.
Solution Approach 2:
The operational amplifier and capacitors in the gain stage are designed to serve multiple functions: they perform both noise cancellation (by generating difference signals) and cyclic A/D conversion. This multi-functionality allows a single circuit to replace what would traditionally require separate noise-canceling circuitry and A/D conversion circuitry, thereby reducing circuit scale.
2Object-affected harmful factors
If separate noise canceling circuit and cyclic A/D converter are integrated, then low-noise readout is achieved, but circuit complexity increases
Solution Approach 1:
The patent merges the noise-canceling circuit and cyclic A/D converter into a single integrated structure where the gain stage with operational amplifier and capacitors serves both functions. This eliminates the need for separate circuits and reduces overall circuit complexity.
Solution Approach 2:
The operational amplifier and capacitors are designed to perform multiple functions: noise cancellation through difference signal generation and cyclic A/D conversion. This multi-functionality reduces circuit complexity by eliminating redundant components and interconnections that would exist in separate circuits.
3Object-affected harmful factors
If conventional noise cancellation with multiple capacitors is used, then noise cancellation is achieved, but processing steps become complicated
Solution Approach 1:
The patent combines the noise cancellation process and cyclic A/D conversion process into a single integrated process that occurs simultaneously in the gain stage. The operational amplifier generates difference signals for noise cancellation while the capacitors participate in both noise cancellation and cyclic A/D conversion, reducing the total number of processing steps.
Solution Approach 2:
The circuit enables continuous operation where noise cancellation and cyclic A/D conversion occur in an integrated manner without requiring separate processing stages. The shared capacitors and operational amplifier allow both functions to be performed continuously and simultaneously, simplifying the processing sequence.
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 configuration simplifies the processing steps and reduces circuit complexity by enabling amplification-type noise cancellation and cyclic A/D conversion using shared components, achieving low-noise readout with reduced circuit size and complexity.
Implementation Method 1
the gain stage performs a process for noise cancellation and amplification to generate a difference signal
Implementation Method 2
the gain stage samples either one of the first and second signal levels into each of the first and second capacitors
Data Source
AI summary
A cyclic A/D converter 21 provides an amplification type noise cancellation process and cyclic A/D conversion in which a plurality of capacitors and an operational amplifier are shared without complicated processing. In the cyclic A/D converter 21, a gain stage 23 uses first to third capacitors 33, 35 and 37 and an operational amplifier circuit 39 to perform the process for noise cancellation and amplification to generate a difference signal between first and second signal levels. In the process for noise cancellation, the difference between the first signal level VR and the second signal level VS is generated. The amplification of this difference is carried out in conjunction with the process for noise cancellation. The gain stage 23 uses the first to third capacitors 33, 35 and 37 and the operational amplifier circuit 39 to perform the process for cyclic A/D conversion of the difference signal. A sub A/D converter circuit 25 receives a signal VOP from an output (e.g., a non-inverting output) 39a of the operational amplifier circuit 39.