Reference Voltage Circuit With Supply Variation Suppression
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Solution Overview
Problem
Existing constant voltage circuits experience significant variations in output voltage due to sudden changes in power supply voltage, which are propagated through parasitic capacitances between depletion mode NMOS transistors.
Innovation Solution
A constant voltage circuit design incorporating a power supply variation suppression circuit with a detection circuit and a pass transistor, connected in series with depletion and enhancement mode transistors, to suppress voltage variations by switching the pass transistor based on power supply changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant voltage circuit uses depletion mode NMOS transistors connected in series, then it can provide a stable reference voltage, but sudden changes in power supply voltage are propagated to the output through parasitic capacitance between drain and source of each transistor
Solution Approach 1:
A pass transistor is introduced as an intermediary component between the power supply variation source and the ED-type reference voltage circuit. This pass transistor acts as a mediator that selectively blocks or transmits voltage variations based on their magnitude, preventing harmful power supply variations from reaching the reference voltage circuit while allowing normal operation signals to pass through.
Solution Approach 2:
The detection circuit continuously monitors power supply voltage variations and activates the pass transistor in advance before significant variation propagation can occur. By detecting variations that exceed a predetermined threshold and preemptively adjusting the pass transistor state, the circuit prevents harmful variations from affecting the reference voltage output.
2Reliability
If a power supply variation suppression circuit is added to reduce output voltage variation, then the circuit complexity increases
Solution Approach 1:
The pass transistor serves multiple functions simultaneously: it acts as a switch to block power supply variations, functions as a controllable resistor for voltage division, and operates as a protective element for the reference voltage circuit. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity.
Solution Approach 2:
The detection circuit provides continuous feedback about power supply voltage variations to control the pass transistor state. This feedback mechanism enables automatic adjustment without requiring complex external control circuits, as the system self-regulates based on real-time monitoring of power supply conditions.
Data Source
AI summary
Provided is a constant voltage circuit with which a variation of an output voltage in response to a sudden change of a power supply voltage is small. The constant voltage circuit includes: an ED-type reference voltage circuit including at least two depletion mode transistors and an enhancement mode transistor which are connected in series; a depletion mode transistor connected in series between the power supply terminal and the ED-type reference voltage circuit; a first output terminal or a second output terminal; and a power supply variation suppression circuit which is connected between a connection point and the ground terminal and which suppresses a variation of the power supply voltage. The power supply variation suppression circuit includes a detection circuit which detects whether there is a variation of the power supply voltage, and a pass transistor which is connected in parallel to the detection circuit.