Capacitive DAC Switching for Faster Voltage Transitions
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Solution Overview
Problem
High-speed digital-to-analog converters require a high driving capability from reference voltage generation circuits to quickly change output voltage in response to digital signal changes, which is a limiting factor in high-speed applications.
Innovation Solution
A capacitive digital-to-analog converter circuit with a second switch network that temporarily couples a circuit node to a third reference voltage during a digital signal transition and decouples it when the transition is complete, using a serial connection of MOS transistors to manage current flow and reduce the need for high driving capability in the reference voltage generation circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large sourcing or sinking current is provided to enable fast voltage change at the output node, then the speed of voltage transition is improved, but the driving capability requirement of the reference voltage generation circuit increases
Solution Approach 1:
The patent introduces a second switch network that is activated in advance during the transition period of the digital signal. This switch network preemptively couples the second circuit node to a third reference voltage, preparing the voltage transition path before the main switching event occurs. By performing this preliminary action, the circuit can achieve faster voltage transitions without requiring the reference voltage generation circuit to continuously provide large driving currents.
Solution Approach 2:
The second switch network acts as an intermediary mechanism between the digital signal input and the capacitor. During the transition period, it temporarily couples the second circuit node to an additional reference voltage, mediating the voltage transition process. This intermediary structure allows the circuit to achieve fast transitions by providing an auxiliary voltage path, thereby reducing the burden on the main reference voltage generation circuit.
2Productivity
If a second switch network is added to provide additional current during transitions, then the speed of digital-to-analog conversion is improved, but the device complexity increases
Solution Approach 1:
The second switch network is designed with dynamic switching characteristics, being activated only during the transition period of the digital signal and automatically decoupling when the transition completes. This dynamic behavior allows the circuit to gain performance benefits during critical transition moments while maintaining simpler operation during steady states, effectively balancing productivity improvement with acceptable device complexity.
Data Source
AI summary
A circuit having a capacitor coupling a first circuit node to a second circuit node; a first switch network configured to couple the second circuit node to either a first reference voltage or a second reference voltage in accordance with a value of a logical signal; and a second switch network configured to couple the second circuit node to a third reference voltage when the logical signal undergoes a transition but decouple the second circuit node from the third reference voltage when the logical signal finishes the transition.