MOS Gm-Controlled Variable Capacitance Circuit for Wide Frequency Tuning

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional capacitor banks have discontinuous capacitance values with a narrow variable range, leading to increased parasitic capacitance and limited effective capacitance, making it difficult to achieve both wide frequency variation and low current consumption in oscillator circuits.

Innovation Solution

A variable capacitance circuit using a transconductance circuit with a MOS transistor, an inductor, and a Gm control circuit that varies the transconductance of the MOS transistor, allowing continuous capacitance value adjustment without increasing parasitic capacitance, and a method to control the capacitance value by varying the gate voltage of a current source MOS transistor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a capacitor bank is used to achieve wide frequency variation, then the capacitance value can be varied, but the capacitance becomes discontinuous and parasitic capacitance increases, limiting the effective capacitance value

Engineering Contradiction:

Improvefrequency variation rangeVSAvoidparasitic capacitance

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the fundamental parameter used for frequency control from capacitance (C) to transconductance (Gm). By controlling the transconductance of the MOS transistor through gate voltage, the circuit achieves continuous frequency variation without relying on switching capacitor banks, thereby avoiding parasitic capacitance accumulation while maintaining wide frequency tuning capability.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the capacitance value is increased to achieve wide frequency range, then frequency variation improves, but current consumption increases due to decreased Q value and reduced Rp

Engineering Contradiction:

Improvefrequency variation rangeVSAvoidcurrent consumption

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent fundamentally changes the control parameter from capacitance to transconductance. The oscillation frequency is controlled by varying the transconductance Gm of the MOS transistor according to the relationship F = 1/(2π√(L/Ceq)) where Ceq = 2/Gm. This allows wide frequency tuning without increasing current consumption because Gm control does not suffer from the Q value degradation that plagues capacitance-based approaches.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If a large number of capacitors are connected in parallel to achieve wide capacitance range, then the variable range increases, but the number of switches increases causing increased parasitic capacitance

Engineering Contradiction:

Improvecapacitance variable rangeVSAvoidnumber of switches

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent eliminates the need for multiple switches and capacitor banks by changing from capacitance switching to transconductance control. A single MOS transistor's transconductance can be continuously varied by adjusting its gate voltage, achieving the same wide tuning range that would otherwise require numerous switched capacitors, thereby dramatically reducing circuit complexity and parasitic elements.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical switching of capacitor banks with electronic control of transistor transconductance. Instead of physically switching between discrete capacitor values using mechanical or electronic switches, the system uses voltage control to continuously adjust the effective capacitance through transconductance modulation, eliminating switch-related parasitics.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables continuous variation of capacitance values and reduces current consumption in oscillator circuits, improving frequency control and minimizing parasitic capacitance effects.

Implementation Method 1

a transconductance circuit that includes a MOS transistor; a Gm control circuit that varies a transconductance of the MOS transistor

Methodology Applied

Scientific EffectTransconductance:

Data Source

PatentUS10566954B2Variable capacitance circuit, oscillator circuit, and method of controlling variable capacitance circuit

Publication Date: 2020.02.18 SONY GROUP CORP

AI summary

A capacitor bank has a capacitance value that is discontinuous and has an extremely narrow variable range. Thus, in a case of obtaining a wide variable range of the capacitance value, a large number of capacitors are connected in parallel and used while being switched by switches. The present technology achieves at least one of: allowing the capacitance value of a variable capacitance circuit to be varied continuously by electrical control without increasing the parasitic capacitance; and decreasing the current consumption of an oscillator circuit using the variable capacitance circuit as compared to a conventional case. The variable capacitance circuit includes: a transconductance circuit that includes a MOS transistor; an inductor that is connected in parallel to the transconductance circuit; and a Gm control circuit that varies a transconductance of the MOS transistor.