SAR ADC Reference Ripple Suppression Using Code-Dependent Cells

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Solution Overview

Problem

Conventional successive approximation register (SAR) analog-to-digital converters (ADCs) face challenges with high power consumption and non-linearity, particularly differential nonlinearity (DNL), due to repetitive switching of the capacitive digital-to-analog converter, which complicates the reference generation circuit and increases silicon area and power usage.

Innovation Solution

A low-complexity code-dependent reference ripple suppression circuit is introduced, utilizing a combination of code-independent and code-dependent compensation cells with logic circuits and compensation capacitors to suppress reference ripple, reducing the number of compensation cells required and minimizing power consumption, where each cell is coupled to receive a reference voltage and output code or bottom-plate voltage signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional SAR ADC uses repetitive switching of capacitive DAC, then conversion function is achieved, but power consumption increases and reference generation circuit becomes complex

Engineering Contradiction:

Improveconversion functionVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent divides the reference generation circuit into multiple code-independent compensation cells, each handling specific switching events. This segmentation allows the circuit to manage repetitive switching operations in a modular fashion, reducing overall complexity and power consumption while maintaining conversion functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The compensation cells are pre-configured to compensate for reference ripple before it affects the conversion accuracy. By performing preliminary compensation actions, the circuit prevents power consumption issues and complexity from arising during the actual conversion process.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If conventional SAR ADC uses repetitive switching of capacitive DAC, then conversion function is achieved, but differential nonlinearity (DNL) increases

Engineering Contradiction:

Improveconversion functionVSAvoiddifferential nonlinearity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The compensation cells use feedback mechanisms to detect and correct reference ripple that causes differential nonlinearity. By continuously monitoring and compensating for ripple effects, the system maintains high conversion accuracy while performing repetitive switching operations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The compensation cells act as intermediary elements between the reference generation circuit and the capacitive DAC. They mediate the reference voltage to eliminate ripple-induced nonlinearity before it reaches the conversion process.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If conventional SAR ADC uses reference generation circuit for repetitive switching, then conversion operation is enabled, but silicon area increases

Engineering Contradiction:

Improveconversion operationVSAvoidsilicon area

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The code-independent compensation cells are designed to handle multiple switching events and different code transitions with a single unified structure. This multi-functionality reduces the total silicon area required compared to having separate compensation circuits for each switching event.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The compensation cells are activated only when needed during specific switching events, allowing the circuit to discard unnecessary compensation operations. This selective activation reduces the effective area required for reference generation while maintaining conversion operation.

Inventive Principle:

Principle #34Discarding and recovering

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 power and area requirements for the reference generation circuit, improving linearity and reducing the number of compensation cells needed, which grows linearly with the number of bits, unlike conventional SAR ADCs where it grows exponentially, thereby enhancing power savings and area efficiency.

Implementation Method 1

a compensation capacitor. A first plate of the compensation capacitor is coupled to receive a reference voltage to be compensated

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10804917B1SAR ADC and a reference ripple suppression circuit adaptable thereto

Publication Date: 2020.10.13 HIMAX TECH LTD

AI summary

A reference ripple suppression circuit adaptable to a successive approximation register (SAR) analog-to-digital converter (ADC) includes a plurality of code-dependent compensation cells, each including a logic circuit and a compensation capacitor. A first plate of the compensation capacitor is coupled to receive a reference voltage to be compensated, and a second plate of the compensation capacitor is coupled to receive an output of the logic circuit performing on an output code of the SAR ADC and at least one logic value representing a bottom-plate voltage of a switched digital-to-analog converter (DAC) of the SAR ADC. (k−1) of the code-dependent compensation cells are required maximally for k-th switching of the SAR ADC.