Inductive MOSFET Biasing for LC Tank Capacitor Switching

Solution Overview

Problem

Existing biasing circuits for switching transistors in voltage controlled oscillators (VCOs) based on LC-tanks face challenges with high chip area usage and increased phase noise due to the need for large bias resistors, which also increase power consumption and reduce the quality factor Q.

Innovation Solution

A biasing circuit and method using a secondary inductor inductively coupled to the primary inductor to provide a high impedance DC bias for the switching transistor, eliminating the need for resistive components and reducing noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a large value bias resistor is used to provide DC bias for the MOSFET switch, then the biasing function is achieved, but the chip area increases significantly

Engineering Contradiction:

Improvebiasing functionVSAvoidchip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent replaces the resistive biasing system with an inductive biasing system. Instead of using a resistor to provide DC bias, a second inductor is inductively coupled to the first inductor (which is part of the LC-tank) to generate the bias voltage for the MOSFET switch. This substitution of resistive component with inductive component resolves the contradiction by eliminating the need for large chip area resistors while maintaining the biasing function.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a second inductor as an intermediary element that is inductively coupled to the first inductor. This second inductor acts as a mediator to transfer energy from the LC-tank to generate the DC bias voltage for the MOSFET switch, thereby eliminating the need for direct resistive connection and reducing chip area consumption.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a large value bias resistor is used to provide DC bias for the MOSFET switch, then the biasing function is achieved, but the quality factor Q decreases and phase noise increases

Engineering Contradiction:

Improvebiasing functionVSAvoidphase noise

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces the resistive biasing system with an inductive biasing system. Instead of using a resistor to provide DC bias, a second inductor is inductively coupled to the first inductor (which is part of the LC-tank) to generate the bias voltage for the MOSFET switch. This substitution of resistive component with inductive component resolves the contradiction by eliminating the need for large chip area resistors while maintaining the biasing function.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a second inductor as an intermediary element that is inductively coupled to the first inductor. This second inductor acts as a mediator to transfer energy from the LC-tank to generate the DC bias voltage for the MOSFET switch, thereby eliminating the need for direct resistive connection and reducing chip area consumption.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If a large value bias resistor is used to provide DC bias for the MOSFET switch, then the biasing function is achieved, but the power consumption increases

Engineering Contradiction:

Improvebiasing functionVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces the resistive biasing system with an inductive biasing system. Instead of using a resistor to provide DC bias, a second inductor is inductively coupled to the first inductor (which is part of the LC-tank) to generate the bias voltage for the MOSFET switch. This substitution of resistive component with inductive component resolves the contradiction by eliminating the need for large chip area resistors while maintaining the biasing function.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces a second inductor as an intermediary element that is inductively coupled to the first inductor. This second inductor acts as a mediator to transfer energy from the LC-tank to generate the DC bias voltage for the MOSFET switch, thereby eliminating the need for direct resistive connection and reducing chip area consumption.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The solution reduces chip area requirements and minimizes phase noise while maintaining a high impedance bias, thereby improving the efficiency and performance of the VCO.

Implementation Method 1

a secondary inductor which is inductively coupled to the primary inductor, the secondary inductor being configured to provide a bias signal for biasing the switching transistor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS10666193B2Biasing circuit for capacitor switch transistor and method therefore

Publication Date: 2020.05.26 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A biasing circuit for biasing a switching transistor, wherein the switching transistor is used for switching a respective capacitor cell into/out of a capacitor array, wherein the capacitor array comprises one or more such capacitor cells, and wherein the capacitor array is coupled in parallel with a primary inductor to form an inductive/capacitive tank. The biasing circuit comprises a secondary inductor which is inductively coupled to the primary inductor, the secondary inductor configured to provide a bias signal for biasing the switching transistor.