Output Buffer Impedance Matching Using External Resistor Feedback
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Solution Overview
Problem
Existing impedance adjusting methods for semiconductor devices are limited by errors in impedance matching due to variations in transistor channel width and require increased circuit area to compensate for quantizing errors, making it difficult to accurately adjust impedance to match external resistors and reduce noise and reflection during high-speed data communication.
Innovation Solution
A semiconductor device with an impedance adjuster that generates an internal reference resistance matching the external resistor, using code signals to adjust the resistance values of resistance adjusters, allowing for precise impedance matching by detecting the resistance ratio between the external resistor and internal resistors, thereby reducing errors and circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the total channel width is adjusted by on/off control of a plurality of transistors, then the impedance of the output buffer can be adjusted, but variations in the channel width of the transistors cause errors in impedance adjustment
Solution Approach 1:
The patent introduces a dummy buffer as an intermediary element to measure the actual impedance characteristics. By measuring the impedance of the dummy buffer (which has the same structure as the output buffer) and using this measurement to control the output buffer, the system achieves precise impedance matching despite transistor variations. The dummy buffer acts as a mediator that translates physical impedance into controllable signals.
Solution Approach 2:
The patent implements a feedback mechanism where the impedance measurement of the dummy buffer is fed back to control the output buffer. The controller continuously monitors the dummy buffer's impedance and adjusts the output buffer's impedance accordingly, creating a closed-loop system that compensates for transistor variations and achieves accurate impedance matching.
2Measurement precision
If a compensation unit is disposed in the output driver to compensate quantizing error, then resistance mismatch between pull-up and pull-down devices is reduced, but the circuit area increases
Solution Approach 1:
The patent merges the compensation function into the existing impedance adjustment mechanism by using the same dummy buffer and controller structure. Instead of adding a separate compensation unit, the system combines impedance measurement, quantizing error compensation, and resistance matching into a single integrated feedback loop, thereby achieving compensation without increasing circuit area.
Solution Approach 2:
The dummy buffer serves multiple functions: it acts as both an impedance measurement reference and a compensation element. The same structure is used for both measuring the output buffer's impedance characteristics and providing the feedback signal for compensation, making the system multi-functional and avoiding additional circuit area.
3Adaptability or versatility
If the impedance of the output buffer is adjusted to an integral multiple of the external resistor value, then the impedance can be matched, but the adjustment is limited and cannot achieve precise matching
Solution Approach 1:
The patent transitions from a static impedance adjustment method (fixed integral multiples) to a dynamic feedback-based method. The controller dynamically adjusts the output buffer's impedance based on real-time measurements of the dummy buffer's impedance, allowing continuous adjustment rather than discrete steps. This dynamic approach enables precise impedance matching at any value, not just integral multiples of the external resistor.
Data Source
AI summary
The present invention is directed to adjust a resistance value of an output buffer on the basis of a resistance value of an external resistor. A potential according to a resistance ratio between an external resistor and each of resistance adjusters is detected by a code generator. In the code generator, code signals for adjusting resistance are adjusted in accordance with the detection result. The resistance value of each of the resistance adjusters is adjusted to an external resistor. Further, by code signals with which the resistance value of each of the resistance adjusters is adjusted to the resistance value of the external resistor, the resistance of the resistance value of an output buffer is adjusted.