Level-Shift Capacitor Bias Current Supply

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Solution Overview

Problem

Amplifiers face failure in providing valid output signals when the input voltage approaches the supply voltage due to insufficient headroom voltage, causing components to be 'squeezed' and preventing the tail current device from operating effectively.

Innovation Solution

A supply circuit incorporating a level-shift capacitor and current source that selectively couples to the supply voltage and amplifier, allowing the capacitor to store charge and provide operational current, maintaining a stable voltage even when input voltages approach the supply voltage, thereby preventing component 'squeezing'.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional charge pump is used to supply current from a boosted voltage, then the tail current device can operate, but low voltage components of the load are stressed

Engineering Contradiction:

Improvetail current device operationVSAvoidstress on low voltage components

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a level shift capacitor as an intermediary energy storage element between the charge pump and the tail current device. The capacitor is charged to a first voltage level during a charge phase, then coupled to provide current at a reduced second voltage level during the sampling phase. This intermediary approach allows the tail current device to receive adequate current without exposing low-voltage components to the full stress of the boosted charge pump voltage.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements periodic charging and discharging of the level shift capacitor through controlled switching between charge and sampling phases. During the charge phase, the capacitor is charged to a higher voltage; during the sampling phase, it provides current at a lower voltage. This periodic action allows the system to maintain reliable tail current operation while protecting low-voltage components from continuous exposure to high stress voltages.

Inventive Principle:

Principle #19Periodic action

2Adaptability or versatility

If the voltage at the input of the amplifier gets close to the supply voltage, then the amplifier can operate with higher input range, but components of the tail current device get squeezed such that there is insufficient head room voltage

Engineering Contradiction:

Improveinput voltage rangeVSAvoidtail current device operation

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent dynamically changes the voltage parameter supplied to the tail current device by using a level shift capacitor that provides a boosted voltage during charge phases and a reduced voltage during sampling phases. This parameter change allows the system to maintain sufficient headroom voltage for reliable tail current device operation even when the amplifier input voltage approaches the supply voltage, thereby expanding the effective input voltage range without sacrificing reliability.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If a level-shift capacitor is used to provide operational current, then the amplifier can provide valid output signals with extended sampling state, but the device complexity increases

Engineering Contradiction:

Improvesampling state durationVSAvoidsupply circuit configuration

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent segments the current supply function into two distinct phases: a charge phase where the level shift capacitor is charged to a higher voltage, and a sampling phase where the capacitor provides current at a reduced voltage. This segmentation is achieved through controlled switching that separates the charging operation from the current provision operation. The segmentation allows the system to extend the sampling state duration while managing device complexity through clear phase separation and dedicated switching control.

Inventive Principle:

Principle #1Segmentation

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

This configuration ensures the amplifier can provide a valid output signal by sourcing current from both the capacitor and current source, extending the sampling state and maintaining a stable operating voltage around 1.1 to 1.3 times the supply voltage, reducing stress on load components compared to conventional charge pumps.

Implementation Method 1

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10541604B2Bias current supply techniques

Publication Date: 2020.01.21 ANALOG DEVICES GLOBAL UNLTD

AI summary

Techniques for supplying a bias current to a load are provided. In certain examples, a circuit can include a level-shift capacitance, a current source, and a load configured to receive a bias current in a first state of the circuit. The current source and the level-shift capacitance can be coupled in series between the load and a supply voltage in the first state. In some examples, during a second state of the circuit, the level-shift capacitance can receive charge, and can be isolated from one of the load or the current source.