Constant-Impedance Transmitter for Variable Logic-High Voltage
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Solution Overview
Problem
Mobile device SOC transmitters face impedance matching issues due to varying logic-high output voltages independent of the power supply voltage, leading to problematic NMOS transistor operation and inefficient data transmission.
Innovation Solution
A transmitter design with multiple pull-up and pull-down legs, each containing thick-oxide and thin-oxide transistors, where a controller adjusts the number of continuously on data transistors to maintain constant output impedance while varying the logic-high output voltage, using parallel segments with resistive paths to match impedance with transmission lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the logic-high output voltage is varied independently of the power supply voltage to support different DRAM modes, then the adaptability to different DRAM operations is improved, but the impedance matching of the transmitter becomes problematic
Solution Approach 1:
The patent applies dynamics by making the transmitter output impedance adjustable through dynamic control of transistor switching states. The controller dynamically switches between different configurations of pull-up and pull-down transistors to maintain constant output impedance (e.g., 50 ohms) while varying the logic-high output voltage to match different DRAM mode requirements. This dynamic adjustment resolves the contradiction between adaptability and impedance matching reliability.
Solution Approach 2:
The patent changes the electrical parameters of the transmitter by varying the number of active pull-up and pull-down transistors to maintain constant output impedance while changing the logic-high output voltage level. By adjusting the effective resistance of the transistor network, the system maintains impedance matching across different operating modes while supporting variable output voltages independent of the power supply voltage.
2Adaptability or versatility
If the NMOS transistor operates in triode mode due to varying output voltage, then the flexibility in output voltage control is improved, but the impedance matching capability deteriorates
Solution Approach 1:
The patent uses dynamic switching control to adjust the operating state of NMOS transistors. Instead of relying on triode mode operation, the controller dynamically switches transistors between on and off states to maintain saturation mode operation and constant output impedance. This dynamic control allows flexible output voltage adjustment while preserving impedance matching capability by preventing the NMOS transistor from entering triode mode.
Solution Approach 2:
The patent changes the effective resistance parameters of the transistor network by controlling the switching states of multiple pull-up and pull-down transistors. This parameter adjustment maintains constant output impedance regardless of the logic-high output voltage level, allowing flexible voltage control while preserving impedance matching capability through coordinated transistor switching.
Data Source
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AI summary
A transmitter (100) is provided with a plurality of pull-up legs (165) and a plurality of pull-down legs (170). A controller (140) controls the pull-up legs and the pull-down legs so that a constant output impedance is provided while supporting a range of logic-high output voltages (at node 115).