Programmable Bus I/O Impedance Circuit With Low Capacitance Switching
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Solution Overview
Problem
Existing input/output structures for integrated circuits, particularly in SRAMs, face challenges in minimizing capacitance while maintaining programming resolution accuracy, especially when switching between driver and termination modes, leading to detrimental effects on data transfer rates due to excessive capacitance and impedance ranges.
Innovation Solution
A combined programmable input and output device with a fixed and programmable portion, utilizing binary-weighted pull-up and pull-down devices, allows for impedance calibration and mode switching to achieve minimum capacitance and optimal impedance ranges, with the termination impedance range being derived from or equal to the driver impedance range, and enable codes applied to appropriate devices to maintain accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a combined programmable input and output device is used to reduce surface area and power consumption, then integration is improved, but capacitance increases and data transfer rates deteriorate
Solution Approach 1:
The combined programmable input and output device is segmented into separate driver portion and termination portion, each with independently controllable pull-up and pull-down devices. This allows selective activation of only the necessary portion (driver or termination) during different operating modes, reducing total capacitance compared to having all devices always connected.
Solution Approach 2:
The device implements dynamic mode switching between driver mode and termination mode through mode control signals. In driver mode, the driver portion is active with appropriate pull-up/pull-down devices enabled; in termination mode, the termination portion is active with different pull-up/pull-down device combinations enabled. This dynamic reconfiguration optimizes capacitance for each operating mode.
2Adaptability or versatility
If the impedance range is extended to support both driver and termination modes, then adaptability is improved, but programming resolution accuracy deteriorates
Solution Approach 1:
Different portions of the device (driver portion and termination portion) have different impedance characteristics optimized for their specific functions. The driver portion uses pull-up and pull-down devices sized for driver impedance ranges, while the termination portion uses devices sized for termination impedance ranges. This local optimization maintains programming resolution accuracy within each function while achieving broad overall adaptability.
Solution Approach 2:
The device changes impedance parameters dynamically based on operating mode. In driver mode, the impedance is set according to driver requirements; in termination mode, the impedance is set according to termination requirements. This parameter switching allows the device to achieve both wide adaptability and high precision within each mode.
3Measurement precision
If binary-weighted pull-up and pull-down devices are used to improve programming resolution, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The binary-weighted pull-up and pull-down devices are segmented into separate driver portion and termination portion groups. Each group independently implements binary-weighted devices for its specific function. This segmentation reduces overall complexity compared to having all devices in a single undifferentiated bank, while maintaining programming resolution accuracy within each portion.
Data Source
AI summary
A combined input and termination circuit comprises a fixed portion of impedance and a programmable portion of impedance. The fixed portion is able to be fixed in a driver mode and a termination mode. The programmable portion is able to be configured to have a desired impedance in a driver mode or a termination mode while maintaining minimum associated capacitance.