Impedance Calibration Circuit With Segmented Codes for Memory Termination
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Solution Overview
Problem
As semiconductor memory device operational speeds increase, signal distortion due to impedance mismatch becomes severe, requiring accurate impedance calibration to maintain termination impedance independence from process, voltage, and temperature variations.
Innovation Solution
An impedance calibration circuit is implemented, comprising code generation circuits and a target impedance code generation circuit, using reference resistors to generate codes for forming target impedance values, reducing driver area and capacitance, and ensuring reliable termination impedance across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single reference resistor is used for impedance calibration, then the circuit complexity is reduced, but the accuracy and reliability of termination impedance across wide-range target impedance values deteriorates
Solution Approach 1:
The impedance calibration circuit is segmented into multiple code generation circuits (first code generation circuit, second code generation circuit, third code generation circuit), each responsible for generating codes for specific impedance ranges. This segmentation allows each circuit to be optimized for its specific range, improving overall reliability while maintaining manageable complexity through modular design.
2Area of stationary object
If the driver area and capacitance are reduced, then the device size and power consumption are minimized, but the ability to provide accurate termination impedance across wide-range target impedance values deteriorates
Solution Approach 1:
The driver circuit is segmented into multiple specialized code generation circuits, each handling a specific impedance range. This allows the total driver area to be distributed efficiently across multiple small functional blocks rather than requiring one large driver, while each block maintains high accuracy for its designated range through dedicated reference resistors and code generation logic.
Solution Approach 2:
Each code generation circuit is equipped with locally optimized reference resistors and code generation logic tailored to its specific impedance range. This local quality ensures that each segment provides high-precision termination impedance for its target range, while the collection of segments collectively covers the wide-range requirement without requiring a large unified driver structure.
3Object-affected harmful factors
If impedance calibration is performed to maintain termination impedance independence from PVT variations, then signal distortion is reduced, but the device complexity and calibration overhead increase
Solution Approach 1:
The calibration circuit is divided into multiple independent code generation circuits, each handling a specific impedance range. This segmentation reduces the complexity of any single calibration block while collectively addressing the full range of PVT variations. Each segment can be independently optimized and tested, simplifying the overall design and verification process.
Solution Approach 2:
The calibration circuit dynamically changes impedance parameters by selecting different reference resistors and generating appropriate codes based on the target impedance value and PVT conditions. This parameter change capability allows the system to maintain accurate termination impedance across varying process, voltage, and temperature conditions without requiring a completely different circuit architecture for each condition.
Data Source
AI summary
An impedance calibration circuit includes a first code generation circuit connected to a first reference resistor, and configured to generate a first code for forming a resistance based on the first reference resistor, by using the first reference resistor; a second code generation circuit configured to form a resistance of a second reference resistor less than the resistance of the first reference resistor, based on the first code, and generate a second code by using the second reference resistor; and a target impedance code generation circuit configured to generate a target impedance code based on the first code, the second code, and a target impedance value, and form an impedance having the target impedance value in a termination driver connected to the impedance calibration circuit, based on the target impedance code.