Latched Comparator Precharge Scheme for Low Kickback Noise
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Solution Overview
Problem
Latching comparators introduce kickback noise due to the manipulation of switches, which limits their precision in comparing input signals.
Innovation Solution
The latching comparator is designed with a precharge phase and a compare phase, where transistors are maintained in saturation mode to reduce switching noise, and isolation modules are used to couple nodes during specific intervals, ensuring that NMOS transistors operate in saturation mode throughout the compare cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If switches are manipulated to control sampling and latching in a latching comparator, then the comparator can perform comparison and latching functions, but kickback noise is introduced at the input nodes
Solution Approach 1:
The comparator operation is divided into distinct phases (precharge phase and compare phase) with separate control logic for each. Switches are controlled independently for precharging nodes versus comparing signals, allowing optimized control for each function and reducing simultaneous switching noise.
Solution Approach 2:
Nodes are precharged to defined voltage levels before the comparison phase begins. This preliminary action ensures that when the compare phase starts, the nodes are already in the correct state, reducing the duration and intensity of switching transients that cause kickback noise.
2Adaptability or versatility
If transistors are allowed to switch during comparison, then the comparator can change state based on input signals, but switching noise couples back to input nodes reducing precision
Solution Approach 1:
Isolation switches act as intermediaries between the input nodes and the internal comparator nodes. During the compare phase, these switches are opened to isolate the input nodes from switching activity in the latch and output stages, preventing kickback noise while still allowing the comparator to change state based on the stored node voltages.
Solution Approach 2:
The comparator operates in periodic cycles with distinct precharge and compare phases. During the compare phase, isolation switches are opened to prevent noise coupling, while state changes are permitted. This periodic switching strategy maintains precision during comparison while enabling necessary state transitions.
Data Source
AI summary
A compare cycle of a comparator includes a precharge phase and a compare phase. During the precharge phase, a node of the comparator is precharged to a defined voltage. In addition, during the precharge phase an input transistor of the comparator is decoupled from the node. During the compare phase, an input voltage is coupled to the node via the input transistor. The input transistor is maintained in saturation during both the precharge phase and the compare phase, reducing switching noise.