DRAM Off-Chip Driver With VCCS for Adaptive Output Impedance
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Solution Overview
Problem
Existing semiconductor memory devices require multiple pull-push circuits to achieve the necessary impedance, leading to increased output capacitance and reduced operation speed due to constant impedance provided by p-type and n-type switch transistors operating at logic high or low voltages.
Innovation Solution
Incorporating a voltage-controlled current source (VCCS) circuit within the off-chip driver (OCD) that adjusts impedance in response to operation voltages between minimum and maximum system voltages, allowing a single pull-push circuit to satisfy impedance requirements and minimize output capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple pull-push circuits are used to achieve the necessary impedance, then the impedance requirement is satisfied, but the output capacitance increases and operation speed decreases
Solution Approach 1:
The patent applies dynamics by making the impedance adjustable rather than fixed. The VCCS circuit responds to operation voltages (ranging from minimum to maximum system voltages) and dynamically adjusts the impedance provided by the pull-push circuit. This allows a single pull-push circuit to satisfy impedance requirements across different operating conditions, eliminating the need for multiple circuits and reducing output capacitance.
Solution Approach 2:
The patent changes the parameter of impedance from a fixed value to a variable parameter that adapts to operation voltages. The VCCS modifies the impedance characteristic based on the applied voltage, enabling one pull-push circuit to replace multiple circuits that would otherwise be needed to cover different impedance requirements. This parameter change resolves the contradiction by maintaining impedance satisfaction while reducing circuit count and capacitance.
2Reliability
If multiple pull-push circuits are used to achieve the necessary impedance, then the impedance requirement is satisfied, but the output capacitance increases
Solution Approach 1:
The VCCS introduces dynamic impedance adjustment capability that allows a single pull-push circuit to provide the necessary impedance across varying operation voltages. This eliminates the need to cascade multiple pull-push circuits, thereby reducing the total output capacitance while still satisfying impedance requirements under all operating conditions.
Solution Approach 2:
The pull-push circuit equipped with VCCS becomes a universal solution that can satisfy impedance requirements across the full range of operation voltages. Instead of needing separate circuits for different voltage conditions, one multi-functional pull-push circuit with adaptive impedance control replaces multiple fixed-impedance circuits, reducing overall capacitance.
3Device complexity
If p-type and n-type switch transistors operate at logic high or low voltages, then the circuit structure is simple, but the impedance is constant and cannot meet varying requirements
Solution Approach 1:
The patent changes the impedance parameter from constant to variable by introducing the VCCS circuit. The VCCS responds to operation voltages and adjusts the impedance accordingly, enabling the pull-push circuit to adapt to varying impedance requirements while maintaining operational simplicity. This parameter change adds adaptability without significantly increasing circuit complexity.
Solution Approach 2:
The introduction of VCCS transforms the static impedance characteristic of traditional pull-push circuits into a dynamic one. The impedance now changes in response to operation voltages, providing adaptability to varying requirements while keeping the overall circuit structure relatively simple through the use of a controlled current source.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables higher operation speed of semiconductor memory devices by reducing the number of required pull-push circuits and lowering output capacitance, while maintaining adjustable impedance within the specified voltage range.
Implementation Method 1
The VCCS is configured to provide, in response to an operation voltage, an impedance with respect to the output pad, wherein the operation voltage ranges between the minimum system voltage and the maximum system voltage
Data Source
AI summary
The present disclosure provides an off-chip driver (OCD) and an associated DRAM. The OCD operates in a power domain. The power domain works under a minimum system voltage and a maximum system voltage. The OCD is configured for providing a drive current to an output pad. The OCD includes a pull-push circuit. The pull-push circuit is coupled to the output pad. The pull-push circuit includes a current source circuit. The current source circuit includes a VCCS. The VCCS is configured to provide, in response to an operation voltage, an impedance with respect to the output pad, wherein the operation voltage ranges between the minimum system voltage and the maximum system voltage.