Impedance Calibration Circuit for Multi-Driver Output Matching
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Solution Overview
Problem
Semiconductor apparatuses face challenges in implementing various impedances to meet driving strength and termination characteristics, leading to suboptimal data transmission performance.
Innovation Solution
An impedance calibration circuit is introduced, featuring replica legs and code generation circuits that calibrate impedance control codes based on voltage comparisons to reference voltages, allowing drivers to adjust impedances to specific target values matching external resistors, thereby optimizing driving strength and termination impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the transmitter circuit is designed to implement various impedances to meet driving strength and termination characteristics, then the adaptability to different specifications is improved, but the device complexity increases
Solution Approach 1:
The transmitter circuit is divided into multiple driver circuits (first driver, second driver, etc.), each responsible for specific data transmission functions. Each driver can be independently configured with different impedance characteristics through separate impedance control codes, allowing the system to achieve various impedance requirements without requiring a completely different circuit design for each specification.
Solution Approach 2:
The impedance characteristics of the drivers are adjusted by changing control parameters (impedance control codes) rather than changing the physical circuit structure. The calibration circuits generate optimized impedance control codes based on measured voltage comparisons, enabling dynamic adjustment of impedance values to match different external resistor configurations and termination requirements.
2Productivity
If impedance calibration is performed to accurately match external resistors, then data transmission performance is improved, but the measurement precision requirements increase
Solution Approach 1:
The calibration circuit employs a feedback mechanism where the voltage at the output node is measured and compared against a reference voltage. Based on this comparison, the calibration circuit adjusts the impedance control codes to minimize the difference between the measured voltage and the reference voltage, thereby optimizing the impedance match. This closed-loop feedback approach enables accurate impedance calibration without requiring extremely high measurement precision throughout the entire system.
Solution Approach 2:
The calibration circuit uses replica legs that replicate the impedance characteristics of the actual drivers. By calibrating the replica legs using voltage comparisons and then applying the same impedance control codes to the actual drivers, the system achieves accurate impedance matching without requiring direct high-precision measurement of the actual driver impedances, thus reducing the measurement precision burden.
Data Source
AI summary
An impedance calibration circuit may include: a first driver having an impedance calibrated according to a first impedance control code, and configured to drive an output terminal according to first data; a second driver having an impedance calibrated according to a second impedance control code, and configured to drive the output terminal according to second data; and an impedance calibration circuit configured to calibrate the first impedance control code to a first target value set to a resistance value of an external resistor, and calibrate the second impedance control code to a second target value different from the resistance value of the external resistor.