Reference Voltage Circuit with Series Depletion MOS and Capacitor

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Solution Overview

Problem

ED type reference voltage circuits take longer to start when a capacitive load is connected, particularly due to increased current consumption, which hinders quick operation.

Innovation Solution

A reference voltage circuit design featuring multiple depletion type MOS transistors connected in series and a capacitor between the connecting point and output terminal, allowing for quick start-up while maintaining low current consumption, even with capacitive loads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the current through the depletion type MOS transistor is reduced to lower current consumption, then current consumption is improved, but the start-up time increases

Engineering Contradiction:

Improvecurrent consumptionVSAvoidstart-up time

Core Design Contradiction:

Use of energy by moving objectVSLoss of time

Solution Approach 1:

The capacitor is pre-charged during the start-up phase through the depletion type MOS transistor before the main output is activated. This preliminary charging action stores energy in the capacitor, enabling the circuit to start up quickly without requiring high continuous current consumption. The capacitor acts as an energy reservoir that is filled in advance (preliminary action) to support the start-up process.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The circuit employs a two-stage operation: an initial start-up phase where the depletion type MOS transistor charges the capacitor, followed by a steady-state phase where the capacitor maintains the output voltage. This periodic switching between charging and holding phases allows the circuit to achieve fast start-up (during the charging phase) while maintaining low current consumption (during the holding phase).

Inventive Principle:

Principle #19Periodic action

2Reliability

If a capacitive load is connected to the output terminal, then the reference voltage can be maintained, but the start-up time increases remarkably

Engineering Contradiction:

Improvereference voltage stabilityVSAvoidstart-up time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The capacitor functions as an intermediary element between the depletion type MOS transistor and the capacitive load. It mediates the energy transfer by being charged by the transistor and then delivering energy to the load, isolating the load's capacitive effect from the transistor. This intermediary action allows the circuit to start up quickly (the capacitor charges rapidly) while still supporting the capacitive load (maintaining reference voltage stability).

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10401891B2Reference voltage circuit and semiconductor device

Publication Date: 2019.09.03 ABLIC INC

AI summary

A reference voltage circuit includes: a depletion type MOS transistor and an enhancement type MOS transistor connected in series, and having gates thereof connected in common, the enhancement type MOS transistor providing a reference voltage from a drain thereof, the depletion type MOS transistor including at least a first depletion type MOS transistor and a second depletion type MOS transistor connected in series; and a capacitor having one end connected to a drain of the first depletion type MOS transistor, and the other end connected to a source of the first depletion type MOS transistor.