Analog Switch Backgate Control for Flat On-Resistance

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Solution Overview

Problem

Conventional CMOS analog switches exhibit significant changes in conduction resistance with varying input voltage and power supply voltage, leading to poor flatness, which is a critical issue for maintaining consistent performance across different voltage conditions.

Innovation Solution

The proposed analog switching circuit employs an NMOS and PMOS configuration with backgate voltage control circuits to regulate the conduction resistance, using logic circuits and control signals to manage the backgate voltages of the transistors based on input and switching control signals, ensuring consistent performance across different voltage conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional CMOS analog switch uses parallel NMOS and PMOS configuration, then bidirectional signal transfer is enabled, but conduction resistance changes significantly with input voltage and power supply voltage

Engineering Contradiction:

Improvebidirectional signal transferVSAvoidconduction resistance flatness

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the backgate voltage of the PMOS transistor based on the input signal voltage level. When the input voltage changes, the backgate voltage is adjusted accordingly to compensate for the resulting conduction resistance changes, thereby maintaining relatively flat overall conduction resistance across different voltage conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback control where the input signal voltage is detected and used to control the backgate voltage of the PMOS transistor. This feedback mechanism automatically adjusts the transistor parameters to compensate for voltage variations, ensuring stable conduction resistance without requiring external intervention.

Inventive Principle:

Principle #23Feedback

2Use of energy by moving object

If power supply voltage is decreased to 5 volts, then energy consumption is reduced, but conduction resistance increases significantly to about 8 ohms

Engineering Contradiction:

Improvepower supply voltageVSAvoidconduction resistance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent changes the operating parameters of the PMOS transistor by adjusting its backgate voltage according to the input signal level. This parameter adjustment compensates for the increased conduction resistance caused by lower power supply voltage, enabling the analog switch to maintain acceptable performance at 5 volts while consuming less energy.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If backgate voltage control circuits are added to regulate conduction resistance, then conduction resistance flatness is improved, but device complexity increases

Engineering Contradiction:

Improveconduction resistance flatnessVSAvoidcontrol circuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the backgate voltage control function with the existing analog switch structure by integrating the control circuitry that uses the input signal itself to regulate the backgate voltage. This integration approach reduces the need for separate external control components and simplifies the overall device structure while achieving improved conduction resistance flatness.

Inventive Principle:

Principle #5Merging (Combining)

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 solution effectively maintains a relatively flat conduction resistance across a range of input voltages and power supply voltages, improving the circuit's performance and reliability.

Implementation Method 1

N-type metal oxide semiconductor field effect transistor (NMOS) having a source, a drain, a gate and a backgate... P-type metal oxide semiconductor field effect transistor (PMOS) having a source, a drain, a gate and a backgate

Methodology Applied

Scientific EffectField Effect: Electric Field

Implementation Method 2

the first control circuit is configured to control the backgate voltage of the NMOS based on the input signal and the switching control signal... the second control circuit is configured to control the backgate voltage of the PMOS based on the input signal and the switching control signal

Methodology Applied

Scientific EffectElectrical Conductivity Control: Electrical Resistance

Data Source

PatentUS8896363B2Analog switching circuit, associated control circuit and method

Publication Date: 2014.11.25 MONOLITHIC POWER SYSTEMS INC

AI summary

The present invention discloses an analog switching circuit having a first terminal receiving an input signal, a second terminal providing an output signal and a control terminal receiving a switching control signal. The analog switching circuit has a first logic circuit providing a first control signal and a second control signal based on the switching control signal; an NMOS and a PMOS coupled between the first terminal and the second terminal, and controlled by the first control signal and the second control signal respectively; a first control circuit controls the backgate voltage of the NMOS based on the input signal and the switching control signal; and a second control circuit controls the backgate voltage of the PMOS based on the input signal and the switching control signal.