Op-Amp Output Control Circuit for Stable Supply-Threshold Enabling
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Solution Overview
Problem
Existing control circuits for operational amplifier circuits often result in unintended output levels when the power supply voltage is low, due to reliance on reference voltage circuits, leading to variations in the power supply voltage level at which the output is enabled.
Innovation Solution
A control circuit that includes a first and second current source, differential pairs, and an output control circuit, which generates currents based on the power supply voltage and bias voltage to control the output node of the operational amplifier circuit, ensuring the output voltage reaches a predetermined level only when the power supply voltage exceeds a specific level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference voltage circuit is used to determine the power supply voltage level, then the control circuit can enable the operational amplifier output at a specific voltage level, but variations in the reference voltage circuit cause the enabling voltage level to vary
Solution Approach 1:
The control circuit uses its own internal operational amplifier and current sources to generate a self-referenced control voltage that directly compares with the power supply voltage. This self-service approach eliminates dependence on external reference voltage circuits, ensuring that the enabling voltage level is determined by the circuit's own stable parameters rather than by variable reference voltages from outside sources.
Solution Approach 2:
The patent introduces a control voltage generated by the circuit's own operational amplifier as an intermediary element. This control voltage serves as a stable reference that mediates between the power supply voltage and the output enable decision. By using this internally-generated intermediary voltage rather than an external reference voltage, the circuit achieves consistent enabling voltage levels despite variations in external reference circuits.
2Speed
If the operational amplifier circuit output is enabled when power supply voltage is low, then the circuit responds quickly, but the output voltage level becomes unintended and unstable
Solution Approach 1:
The control circuit continuously generates and maintains a control voltage through its operational amplifier and current sources before the power supply voltage reaches the enabling threshold. This preliminary action ensures that when the power supply voltage does reach the threshold, the comparison and enable decision can occur immediately without delay, while the control voltage is already prepared and stable to ensure accurate output voltage level.
Solution Approach 2:
The operational amplifier in the control circuit provides feedback to continuously adjust and maintain the control voltage based on the power supply voltage level. This feedback mechanism ensures that the control voltage accurately reflects the power supply voltage state, enabling the circuit to respond quickly when the threshold is reached while maintaining reliable and accurate output voltage level through continuous monitoring and adjustment.
Data Source
AI summary
A control circuit configured to control an operational amplifier circuit that includes a first current source generating a first current according to a power supply voltage and a bias voltage, a first differential pair receiving a pair of input voltages and allowing the first current to flow therethrough, and a first output circuit applying an output voltage according to the input voltages to an output node. The control circuit includes: a second current source generating a second current according to the power supply voltage and the bias voltage; a second differential pair receiving the input voltages and allowing the second current to flow therethrough; and an output control circuit that causes a level at the output node to be a predetermined level, and causes the output voltage to be applied the output node, respectively before and after the level of the power supply voltage reaches a predetermined level.