Comparator Stack-Gate Circuit for Kickback Noise Cancellation
Find Innovative SolutionsGenerate Solutions
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 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 switches that connect internal nodes of a differential pair of stack-gate transistors to a power-supply pin or each other, ensuring equal kickback noise when the comparator is turned on, allowing differential operation to cancel out noise effectively.
Engineering Contradictions & Design Principles
Engineering 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
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 cancelled by the differential operation, thus preventing performance degradation
2Use of energy by moving object
If the comparator operates in off-mode with floating internal nodes, then power consumption is reduced, but uncontrolled internal nodes induce unequal kickback noise
Solution Approach 1:
The patent implements preliminary action by pre-configuring the switches to connect internal nodes to power supply or ground during the off-mode operation. This preliminary connection ensures that internal nodes have controlled voltages before the comparator is activated, so when power is reduced during off-mode, the kickback noise remains equal and cancellable, resolving the contradiction between low power consumption and noise control
3Reliability
If a single transistor with long channel length is used, then circuit performance is improved, but such transistors are no longer available in scaled semiconductor process nodes
Solution Approach 1:
The patent applies segmentation by dividing a single long-channel transistor into multiple short-channel transistors connected in series (stack-gate structure). Each transistor in the stack has a small channel length compatible with scaled process nodes, but their series connection creates an equivalent long-channel transistor, thus achieving both compatibility with modern scaled processes and the desired circuit performance
Data Source
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.