Voltage Detection Circuit with Start-Up Gating at Low Supply Voltage
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Solution Overview
Problem
Conventional voltage detectors with NMOS transistors having the same aspect ratio face issues with a high minimum operating power supply voltage, leading to erroneous detection below this voltage due to non-saturation operation, especially at high temperatures.
Innovation Solution
A voltage detector design using a depletion-type MOS transistor as a current source and an enhancement-type MOS transistor in a current mirror circuit, combined with a start-up circuit to ensure operation above the minimum power supply voltage, maintaining flat temperature characteristics and preventing erroneous detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If NMOS transistors 51 and 52 have approximately the same aspect ratio to achieve flat temperature characteristics of detection voltage, then the temperature characteristics are improved, but the minimum operating power supply voltage increases to about 0.6V at high temperature
Solution Approach 1:
The voltage detector is divided into two independent functional blocks: a voltage detection circuit (containing transistors 51, 52 and generating detection voltage) and a start-up circuit (containing transistors 61, 62, 63 and generating enable signal). This segmentation allows each block to be optimized independently - the voltage detection circuit maintains flat temperature characteristics while the start-up circuit ensures proper operation by enabling detection only when power supply voltage exceeds the minimum threshold.
2Power
If the minimum operating power supply voltage is reduced below 0.6V, then power consumption is improved, but erroneous detection occurs when power supply voltage is below the minimum operating voltage due to non-saturation operation of transistor 51
Solution Approach 1:
The start-up circuit performs preliminary action by generating an enable signal before the voltage detection circuit operates. This enable signal indicates that the power supply voltage has exceeded the minimum operating threshold, ensuring that transistor 51 will operate in saturation region. This preliminary check prevents erroneous detection from occurring in the first place.
Solution Approach 2:
The enable signal acts as an intermediary between the power supply voltage and the voltage detection circuit. It mediates the operation by enabling detection only when conditions are appropriate (power supply voltage > minimum operating voltage), thus preventing erroneous detection without requiring the voltage detection circuit itself to operate at higher voltages.
3Reliability
If a start-up circuit is added to prevent erroneous detection below minimum operating voltage, then reliability is improved, but device complexity increases
Solution Approach 1:
The start-up circuit is merged with the voltage detection circuit to form a unified voltage detector system. The start-up circuit uses the same power supply voltage and shares the enable signal path with the voltage detection circuit, allowing both functions to be implemented in a compact integrated structure rather than as separate independent circuits.
Data Source
AI summary
A voltage detector includes a voltage detection circuit including: a first current mirror circuit into which a current of a first current source composed of a depletion-type MOS transistor, is input; an enhancement-type first MOS transistor having a gate connected to an input port a drain connected to an output port and the first current mirror circuit; and a switch circuit controlled by an enable signal received by a control port; and a start-up circuit including: a current detection circuit that outputs the enable signal upon detecting that an output current of a second current mirror circuit, into which a current of a second current source is input, has become equal to or greater than a predetermined current. The voltage detection circuit outputs a detection signal corresponding to a voltage of the input port from the output port in response to receiving the enable signal at the switch circuit.