Op-Amp Output Enable Circuit for Charge Coupling Isolation
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Solution Overview
Problem
Operational amplifiers experience voltage redistribution and charge coupling effects due to switching operations of the output enable switch, leading to deviations in internal node voltages, which affect bias voltage levels.
Innovation Solution
An operational amplifier design incorporating an input stage, output stage, output enable switch, internal capacitor, and coupling effect reduction circuit, where the coupling effect reduction circuit is turned off during operational periods to prevent coupling charge from affecting input stage voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the output enable switch is turned on to drive the load, then the voltage buffer can drive the load, but charge redistribution occurs causing internal node voltage to deviate from designed level
Solution Approach 1:
The patent introduces a coupling effect reduction circuit as an intermediary element between the output enable switch and the internal capacitor. This circuit includes a switch that can be controlled to open during the enable transition period, thereby blocking the direct coupling path that would otherwise allow charge redistribution to affect the internal node voltage. The intermediary switch acts as a mediator that permits normal operation when needed while preventing harmful coupling effects during switching transitions.
2Ease of operation
If the output enable switch is turned off to open circuit between voltage buffer and load, then the voltage buffer cannot drive the load, but charge redistribution still occurs affecting bias voltage levels
Solution Approach 1:
The patent applies preliminary anti-action by proactively opening the coupling effect reduction circuit switch before or during the enable switch transition. This preliminary action prevents the charge redistribution from occurring in the first place, rather than attempting to correct the voltage deviation after it occurs. By anticipating and preventing the harmful coupling effect during the switching operation, the bias voltage stability is maintained throughout the enable/disable transition.
3Adaptability or versatility
If compensation capacitor or circuit parasitic capacitance is present in voltage buffer, then voltage buffer can function with timing control, but charge redistribution causes coupling effect that deviates internal node voltage from designed level
Solution Approach 1:
The patent extracts or removes the harmful coupling effect from the system by introducing a switch in the coupling effect reduction circuit that can be opened to disconnect the path through which charge redistribution affects the internal node. This extraction approach separates the useful timing control functionality (which relies on the capacitor) from the harmful coupling effect, allowing the former to operate while preventing the latter from degrading voltage precision.
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
Effectively separates voltage redistribution and charge coupling effects from internal nodes, maintaining stable bias voltage levels during output enable switch operations.
Implementation Method 1
For a voltage buffer having an internal circuit design with a compensation capacitor or with circuit parasitic capacitance, the above occurrence of the charge redistribution could result in a coupling effect
Implementation Method 2
the coupling effect reduction circuit, coupled between the internal capacitor and the output node or between the internal capacitor and the input stage, is turned off during an operational period that begins from the start time point, so as to prevent coupling charge generated when the output enable switch is turned on from affecting operational voltage levels of the input stage
Data Source
AI summary
An operational amplifier includes an input stage, an output stage, an output enable switch, an internal capacitor, a coupling effect reduction circuit. The input stage provides an intermediate signal according to an input signal. The output stage, including an output node, provides a driving signal according to the intermediate signal. The output enable switch is turned on during an output enable period, having a start time point, to drive a load with the driving signal. The internal capacitor is coupled between the input stage and the output stage. The coupling effect reduction circuit, coupled between the internal capacitor and the output node or between the internal capacitor and the input stage, is turned off during an operational period starting from the start time point, to prevent coupling charge generated when the output enable switch is turned on from affecting operational voltage levels of the input stage.