Dynamic I/O Buffer Impedance Calibration for Split Termination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed signal integrity issues arise in chip-to-chip interconnects due to transmission line effects like reflections, attenuation, and cross-talk, particularly in SDRAM memory systems, where existing solutions lack dynamic impedance control and often require external resistors, increasing cost and power consumption.
Innovation Solution
A combined drive and termination circuit with variable impedance pull-up and pull-down networks, dynamically switched between two impedance settings, and calibrated using a controller to match the characteristic impedance of the transmission line, allowing for both drive and termination modes of operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed external resistors are used for termination, then signal integrity is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the drive buffer and termination resistor into a single integrated circuit block. The termination function is merged with the drive buffer, eliminating the need for separate external termination resistors. This is achieved through circuit topology where the buffer output stage directly provides the termination impedance to match the transmission line.
Solution Approach 2:
The drive buffer is designed to perform multiple functions: signal driving and termination impedance matching. By making the buffer universal, it can operate in different modes (drive mode and termination mode) depending on the state of control signals, thereby eliminating the need for dedicated external termination components.
2Reliability
If fixed external resistors are used for termination, then signal integrity is improved, but power consumption increases
Solution Approach 1:
The termination impedance is made dynamic rather than fixed. The circuit can switch between different impedance states based on control signals, allowing the termination to be activated only when needed. This dynamic behavior reduces continuous power dissipation that would occur with fixed external resistors always connected.
Solution Approach 2:
The termination function is activated periodically or selectively based on signal conditions rather than continuously. The control logic enables termination only during specific operation phases or when signal reflections are detected, reducing overall power consumption compared to continuous termination provided by external resistors.
3Strength
If I/O buffers have low output impedance, then signal swing is improved, but signal reflections increase
Solution Approach 1:
The output impedance of the I/O buffer is made dynamically adjustable rather than fixed at a low value. The buffer can switch between low impedance mode (for strong signal driving) and high impedance mode (for reflectionless termination) based on operational requirements and control signals.
Solution Approach 2:
The impedance parameter of the buffer is changed dynamically to match different operational requirements. By adjusting the output impedance parameter to match the transmission line characteristic impedance, reflections are minimized while maintaining strong signal swing capability when needed.
Data Source
AI summary
A system and method of performing off chip drive (OCD) and on-die termination (ODT) are provided. A common pull-up network composed of transistors and a common pull-down network composed of transistors are employed to implement both of these functions. In drive mode, the pull-up network is configured to produce a calibrated drive impedance when an “on” output is to be generated, and the pull-up network is configured to produce a calibrated drive impedance when an “off” output is to be generated. In termination mode, the pull-up network and the pull-down network are configured to produce a calibrated pull-up resistance and pull-down resistance respectively such that together, they form a split termination.