On-Die Memory Bus Termination Impedance Control Without Fuse Banks
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Solution Overview
Problem
Conventional on-die termination (ODT) circuits in memory devices suffer from imprecise resistance control due to polysilicon resistor fabrication limitations, leading to signal reflections and reduced timing margins, which are further affected by temperature and voltage variations, necessitating costly and time-consuming testing and reprogramming during fabrication.
Innovation Solution
An ODT system that omits the fuse bank and uses a termination resistance determining circuit to measure and adjust the impedance of polysilicon resistors, applying digital signals to transistors to achieve precise impedance matching, either directly through resistance measurement or indirectly by accounting for temperature and voltage changes, without the need for reprogramming after packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional ODT circuits use polysilicon resistors for termination, then the device can be manufactured with standard fabrication processes, but the resistance control precision is insufficient leading to signal reflections
Solution Approach 1:
The patent changes the resistance value of polysilicon resistors by controlling fabrication parameters (thickness, width, length) and uses digital-to-analog conversion to dynamically adjust termination resistance values. This allows precise impedance matching (±1 ohm) to be achieved by changing physical and electrical parameters rather than relying solely on fabrication precision.
Solution Approach 2:
The patent replaces the mechanical/fabrication-based resistance control with an electrical control system. Instead of relying on precise physical resistor fabrication, the system uses digital control signals converted to analog voltages that electronically adjust the termination resistance, substituting electrical precision for mechanical fabrication precision.
2Manufacturing precision
If fuse banks are added for reprogramming during fabrication testing, then impedance matching can be adjusted, but fabrication complexity and cost increase significantly
Solution Approach 1:
The patent extracts and eliminates the fuse bank component from the conventional ODT circuit. Instead of adding complex reprogramming infrastructure, the invention uses a simplified digital control interface that directly adjusts termination resistance without requiring fuse banks, testing infrastructure, or reprogramming capabilities.
Solution Approach 2:
The termination resistance is self-adjusted through digital control signals that automatically set the appropriate resistance value based on operating conditions. The system serves itself by using onboard digital-to-analog conversion and control logic to maintain optimal impedance matching without external intervention or complex fabrication testing.
3Ease of manufacture
If polysilicon resistor values are used as-is from fabrication, then manufacturing is simple, but temperature and voltage variations cause impedance drift
Solution Approach 1:
The patent implements feedback control where digital control logic monitors operating conditions and adjusts termination resistance values accordingly. The digital-to-analog converter receives control signals and dynamically adjusts the resistance to compensate for temperature and voltage variations, maintaining stable impedance matching throughout device operation.
Solution Approach 2:
The termination resistance is made dynamic rather than static. Instead of fixed polysilicon resistor values, the system uses controllable resistance elements that can change their resistance values in response to operating conditions, allowing the impedance to adapt and remain stable despite environmental variations.
Data Source
AI summary
A system for controlling the termination impedance of memory device data bus terminals is fabricated on the same die as the memory device. The system includes a termination resistor connected to each data bus terminal, which is connected in parallel with several transistors that are selectively turned on to adjust the termination impedance. The transistors are controlled by a circuit that determines the resistance of the termination resistor and turns on the correct number of transistor to properly set the termination impedance. In one example, the resistance of the termination resistor is determined by directly measuring a resistor of the same type as the termination resistor. In another example, the resistance of the termination resistor is determined indirectly by measuring parameters that affect the resistance of the termination resistor. In either case, the system can maintain the termination impedance of the data bus terminals constant despite changes in the termination resistor.