Ramp and Injection DAC Circuit for Small-Area Image Sensor ADCs

Solution Overview

Problem

Existing DAC circuits for high-resolution image sensors require a large number of AD conversion circuits, leading to increased area and power consumption, and there is a need for a DAC circuit that generates a ramp signal with a small-scale circuit configuration.

Innovation Solution

A DAC circuit comprising a ramp DAC that generates a voltage ramp signal with a constant time gradient, an injection DAC that outputs a predetermined voltage during reset periods, and an adding circuit that combines the outputs of both DACs to provide a comparison reference voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the number of AD conversion circuits is increased to reduce the number of photoelectric conversion elements per AD conversion circuit, then the imaging frame rate increases and in-plane skew decreases, but the circuit area and power consumption increase

Engineering Contradiction:

Improveimaging frame rateVSAvoidcircuit area

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The DAC circuit is segmented into two independent functional blocks: a ramp DAC for generating the ramp signal and an injection DAC for injecting reset voltage. This segmentation allows each block to be optimized independently for minimal area while maintaining the required functionality for high frame rate operation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The injection DAC serves multiple functions: it provides reset voltage injection during the reset period, contributes to the comparison reference voltage during the conversion period through the adding circuit, and enables the circuit to achieve both high frame rate and small area. This multi-functionality reduces the need for separate dedicated circuits.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Productivity

If the number of AD conversion circuits is increased to reduce the number of photoelectric conversion elements per AD conversion circuit, then the imaging frame rate increases and in-plane skew decreases, but the power consumption increases

Engineering Contradiction:

Improveimaging frame rateVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The DAC circuit is segmented into two independent functional blocks: a ramp DAC for generating the ramp signal and an injection DAC for injecting reset voltage. This segmentation allows each block to be optimized independently for minimal area while maintaining the required functionality for high frame rate operation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The injection DAC operates periodically during the reset period rather than continuously, injecting reset voltage only when needed. This periodic operation reduces power consumption compared to continuous operation, while still achieving the required high frame rate performance through efficient timing.

Inventive Principle:

Principle #19Periodic action

3Device complexity

If a traditional single DAC circuit is used to generate the comparison reference voltage, then the circuit configuration is simple, but the circuit area and power consumption are large

Engineering Contradiction:

Improvecircuit configurationVSAvoidcircuit area

Core Design Contradiction:

Device complexityVSArea of stationary object

Solution Approach 1:

The DAC circuit is segmented into two independent functional blocks: a ramp DAC for generating the ramp signal and an injection DAC for injecting reset voltage. This segmentation allows each block to be optimized independently for minimal area while maintaining the required functionality for high frame rate operation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The outputs of the ramp DAC and injection DAC are merged through the adding circuit to generate the final comparison reference voltage. This combining approach allows two simple, small-area DAC blocks to work together to achieve the functionality of a more complex traditional DAC circuit with smaller total area.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS11159173B2DAC circuit, solid-state imaging element, and electronic equipment

Publication Date: 2021.10.26 SONY SEMICON SOLUTIONS CORP

AI summary

The present technology relates to a DAC circuit, a solid-state imaging element, and electronic equipment that can be achieved with a small-scale circuit configuration. The DAC circuit includes: a ramp DAC that generates a ramp signal that changes in voltage with a constant time gradient; an injection DAC that outputs a predetermined voltage during a reset period for resetting a comparison target voltage to be compared with the ramp signal; and an adding circuit that adds an output of the ramp DAC and an output of the injection DAC and outputs the outputs to a comparison circuit as a comparison reference voltage. The present technology can be applied to, for example, a DAC circuit of a solid-state imaging element, and the like.