Voltage-Controlled Oscillator AFC Circuit Without Op-Amp Noise

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing voltage control oscillators using operational amplifiers suffer from unwanted voltage noise affecting C/N ratio and require additional chip area for phase compensation, hindering miniaturization.

Innovation Solution

A voltage control oscillator with a resistance voltage dividing circuit formed by switching elements, allowing arbitrary gain and reference value adjustments, reducing noise and improving C/N ratio without capacitors, and minimizing IC chip area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If an operational amplifier is used for AFC function, then gain adjustment and reference adjustment are achieved, but unwanted voltage noise is applied to the varactor deteriorating C/N

Engineering Contradiction:

ImproveAFC functionVSAvoidvoltage noise

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the noise-generating operational amplifier from the AFC circuit and replaces it with a noise-free resistance voltage dividing circuit formed by switching elements. This removes the harmful noise source while preserving the AFC gain adjustment function through the voltage dividing circuit.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent substitutes the electronic operational amplifier system with a switching element-based resistance voltage dividing system. This replacement eliminates the noise inherent in operational amplifiers while achieving the same AFC control functionality through resistive voltage division.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If an operational amplifier is used for AFC function, then gain adjustment is achieved, but a capacitor for phase compensation is required increasing chip area

Engineering Contradiction:

ImproveAFC functionVSAvoidchip area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent removes the phase compensation capacitor that is normally required with operational amplifiers. The switching element-based voltage dividing circuit inherently provides stable operation without needing external capacitive compensation, thus reducing chip area.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the operational amplifier plus capacitor compensation system with a pure resistive voltage dividing circuit using switching elements. This substitution eliminates the need for phase compensation capacitors while maintaining circuit stability and AFC functionality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If an operational amplifier is used for AFC function, then arbitrary gain change is achieved, but device complexity increases

Engineering Contradiction:

Improvegain adjustmentVSAvoidcircuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent extracts the complex operational amplifier circuitry and replaces it with simple switching elements forming a resistance voltage dividing circuit. This simplification maintains the gain adjustment capability while dramatically reducing circuit complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent substitutes the complex operational amplifier-based gain control system with a simpler switching element-based resistive voltage divider. This replacement achieves arbitrary gain change through switching different resistance combinations, reducing overall device complexity.

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

The solution effectively reduces noise and enhances the C/N ratio while reducing IC chip area, achieving these improvements at a lower cost without the need for capacitors.

Implementation Method 1

the gain adjustment circuit controls the plurality of switching elements and thus forms a voltage dividing circuit between the reference bias voltage and the external control voltage terminal so as to generate an AFC voltage

Methodology Applied

Scientific EffectVoltage division: Ohm's Law

Data Source

PatentUS7847640B2Voltage controlled oscillator

Publication Date: 2010.12.07 SEIKO EPSON CORP

AI summary

A voltage controlled oscillator controls an oscillation frequency based on a control voltage supplied from an external control voltage terminal. The voltage controlled oscillator includes a reference bias voltage circuit and a gain adjustment circuit. The reference bias voltage circuit includes multiple serial resistances between a reference voltage and a ground. The reference bias voltage circuit controls a switch coupled in parallel to at least one of the serial resistances and thus changes a voltage dividing ratio of the serial resistances so as to set a reference bias voltage. The gain adjustment circuit adjusts a gain of the control voltage. The gain adjustment circuit includes multiple resistances and multiple switching elements. The gain adjustment circuit controls the switching elements to form a voltage dividing circuit between the reference bias voltage and the external control voltage terminal so as to generate an automatic frequency control voltage.