Comparator Input Circuit for Equalized Kickback Noise

Solution Overview

Problem

In integrated circuits, particularly in comparators with stack-gate structures, internal nodes can induce unequal kickback noise when the comparator operates, degrading performance and leading to a poor signal-to-noise ratio (SNR) in analog-to-digital converters (ADCs) due to uncontrolled voltages during off-mode operations.

Innovation Solution

The introduction of a new circuit design where internal nodes of a differential pair of stack-gate transistors are connected or tied to a power-supply pin, and additional switches are used to ensure equal kickback noise generation when the comparator is turned on, allowing differential operation to cancel out this noise effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple stages of gates of transistors are stacked to form an equivalent transistor with long channel length, then input-offset and input-referred noise are reduced, but internal nodes induce unequal kickback noise that degrades comparator performance

Engineering Contradiction:

Improveinput-offset and input-referred noiseVSAvoidkickback noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by connecting switches to the internal nodes of the stack-gate transistors before the comparator operation. These switches are pre-configured to equalize the voltages at internal nodes during the off-mode (pre-charge operation), ensuring that when the comparator is turned on, the kickback noise from both sides is equal and can be effectively canceled by the differential operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements equipotentiality by using switches to connect internal nodes to common voltage references (such as power supply pins or ground) during the off-mode. This ensures that both sides of the differential pair have equal potentials at their internal nodes, creating symmetric conditions that result in equal kickback noise that the differential comparator can reject.

Inventive Principle:

Principle #12Equipotentiality

2Device complexity

If internal nodes of stack-gate transistors are left floating during off-mode operation, then device complexity is reduced, but uncontrolled voltages at internal nodes cause unequal kickback noise

Engineering Contradiction:

Improvecircuit structureVSAvoidunequal kickback noise

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by connecting switches to the internal nodes of the stack-gate transistors before the comparator operation. These switches are pre-configured to equalize the voltages at internal nodes during the off-mode (pre-charge operation), ensuring that when the comparator is turned on, the kickback noise from both sides is equal and can be effectively canceled by the differential operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements equipotentiality by using switches to connect internal nodes to common voltage references (such as power supply pins or ground) during the off-mode. This ensures that both sides of the differential pair have equal potentials at their internal nodes, creating symmetric conditions that result in equal kickback noise that the differential comparator can reject.

Inventive Principle:

Principle #12Equipotentiality

3Object-generated harmful factors

If switches are added to connect internal nodes to power-supply pin to ensure equal kickback noise, then kickback noise is reduced, but device complexity increases

Engineering Contradiction:

Improvekickback noiseVSAvoidcircuit structure

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by connecting switches to the internal nodes of the stack-gate transistors before the comparator operation. These switches are pre-configured to equalize the voltages at internal nodes during the off-mode (pre-charge operation), ensuring that when the comparator is turned on, the kickback noise from both sides is equal and can be effectively canceled by the differential operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements equipotentiality by using switches to connect internal nodes to common voltage references (such as power supply pins or ground) during the off-mode. This ensures that both sides of the differential pair have equal potentials at their internal nodes, creating symmetric conditions that result in equal kickback noise that the differential comparator can reject.

Inventive Principle:

Principle #12Equipotentiality

Data Source

PatentUS10819316B2Circuits and methods for reducing kickback noise in a comparator

Publication Date: 2020.10.27 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Circuits and methods for reducing and cancelling out kickback noise are disclosed. In one example, a circuit for a comparator is disclosed. The circuit includes: a first transistor group, a second transistor group, and a first switch. The first transistor group comprises a first transistor having a drain coupled to a first node, and a second transistor having a source coupled to the first node. Gates of the first transistor and the second transistor are coupled together to a first input of the comparator. The second transistor group comprises a third transistor having a drain coupled to a second node, and a fourth transistor having a source coupled to the second node. Gates of the third transistor and the fourth transistor are coupled together to a second input of the comparator. The first switch is connected to and between the first node and the second node.