Memory Controller Output Impedance Matching Without PCB Resistors
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Solution Overview
Problem
In synchronous dynamic random-access memory (SDRAM) circuits, the lack of termination resistors on certain pins leads to signal reflection issues, necessitating additional resistors on the printed circuit board (PCB) and limited winding length, increasing costs, area, and layout complexity.
Innovation Solution
A memory controller with dual driving and impedance matching circuits, controlled by a logic circuit, adjusts impedance and driving capability to output control signals without the need for additional PCB resistors, allowing for flexible circuit design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If matching resistors are installed on the PCB to reduce signal reflection, then signal quality is improved, but PCB area and cost increase
Solution Approach 1:
The patent combines the matching resistor function with the output driver circuit by integrating an adjustable impedance circuit directly into the memory controller. This merging eliminates the need for separate external resistors on the PCB, thereby reducing PCB area while maintaining signal quality through active impedance adjustment.
Solution Approach 2:
The patent introduces an adjustable impedance circuit as an intermediary between the output driver and the transmission line. This intermediary actively adjusts the output impedance to match the transmission line impedance, replacing the passive external resistors and reducing the need for additional PCB components.
2Reliability
If matching resistors are installed on the PCB to reduce signal reflection, then signal quality is improved, but cost increases
Solution Approach 1:
The patent combines the matching resistor function with the output driver circuit by integrating an adjustable impedance circuit directly into the memory controller. This merging eliminates the need for separate external resistors on the PCB, thereby reducing component count and assembly cost while maintaining signal quality.
Solution Approach 2:
The adjustable impedance circuit automatically adjusts the output impedance to match the transmission line impedance without requiring external components or manual adjustment. This self-service capability eliminates the need for external matching resistors, reducing both component cost and assembly complexity.
3Reliability
If winding length on the PCB is limited to reduce signal reflection, then signal quality is improved, but circuit layout difficulty increases
Solution Approach 1:
The patent introduces an adjustable impedance circuit as an intermediary that actively matches the output impedance to the transmission line impedance. This allows for more flexible PCB layout with less stringent winding length constraints, as the active impedance matching compensates for transmission line effects that would otherwise require strict length control.
Solution Approach 2:
The patent uses a dynamic adjustable impedance circuit that can adapt the output impedance in real-time, replacing static passive resistors. This dynamic adjustment provides greater tolerance for variations in transmission line characteristics, allowing more flexible PCB routing and reducing layout constraints.
4Reliability
If additional matching resistors are used to reduce signal reflection, then signal overshoot and undershoot requirements are met, but device complexity increases
Solution Approach 1:
The patent merges the impedance matching function with the output driver circuit by integrating an adjustable impedance circuit inside the memory controller. This consolidation reduces the number of discrete external components needed for signal integrity, thereby reducing overall device complexity while maintaining control over signal overshoot and undershoot.
Solution Approach 2:
The adjustable impedance circuit automatically performs impedance matching and signal integrity control without requiring external passive components. This self-service approach integrates multiple functions into a single active circuit, reducing the overall component count and system complexity compared to using external matching resistors.
Data Source
AI summary
A memory controller adjusts impedance matching of an output terminal and outputs a control signal that controls a memory through the output terminal. The memory controller includes a first driving and impedance matching circuit, a second driving and impedance matching circuit, and a logic circuit. The logic circuit, which is coupled to the first driving and impedance matching circuit and the second driving and impedance matching circuit, sets a first impedance and a first driving capability of the first driving and impedance matching circuit, sets a second impedance and a second driving capability of the second driving and impedance matching circuit, and enables the first driving and impedance matching circuit to cause the control signal to have a first level or enables the second driving and impedance matching circuit to cause the control signal to have a second level different from the first level.