Variable Core VCO Temperature Compensation via Digital Lookup

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Solution Overview

Problem

Traditional voltage-controlled oscillators (VCOs) face challenges with temperature drift and stability due to thermal fluctuations, and the use of methods like tempco resistors and heating transistors adds manufacturing costs and complexity, while digital control methods suffer from resolution and switching artifacts.

Innovation Solution

A variable core VCO design that allows charging and discharging with opposite polarity, controlled by a microprocessor, using a combination of analog and digital control voltages to generate complex waveforms, including arbitrary waveforms, and enabling modulation of control voltages through high-resolution DACs and PWM, with a controller that selects and combines control voltage inputs for precise waveform generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If tempco resistors and heated transistor junctions are used to overcome temperature drift, then temperature stability is improved, but manufacturing cost and device complexity increase

Engineering Contradiction:

Improvetemperature stabilityVSAvoiddevice complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent extracts the temperature-dependent exponential function from the oscillator core by using a digital lookup table stored in memory. The DAC converts digital values from the table to analog control voltages, separating the temperature compensation function from the oscillator circuitry. This eliminates the need for tempco resistors and heated junctions while maintaining temperature stability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the physical/thermal system (heated transistor junctions and tempco resistors) with a digital system. The microprocessor generates control voltages through a DAC based on pre-calculated lookup tables, substituting thermal compensation methods with digital signal processing to achieve temperature-independent operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If tempco resistors and heated transistor junctions are used to overcome temperature drift, then temperature stability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvetemperature stabilityVSAvoidmanufacturing cost

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

The patent uses standard, inexpensive components (ordinary resistors, capacitors, and a DAC) instead of costly specialized components like tempco resistors and highly matched transistor packages. The temperature compensation is achieved through software (lookup tables) rather than expensive hardware, significantly reducing manufacturing costs while maintaining stability.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent replaces expensive thermal compensation hardware with a digital implementation using a microprocessor and DAC. The lookup tables contain pre-calculated exponential values that are converted to analog control voltages, eliminating the need for costly tempco resistors and heated junctions while achieving temperature stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If digital control methods are used to generate control voltages, then ease of control is improved, but resolution and switching artifacts worsen

Engineering Contradiction:

Improveease of controlVSAvoidcontrol voltage resolution

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent pre-calculates and stores exponential function values in a lookup table in memory before operation. During runtime, the microprocessor simply retrieves pre-computed values from the table and converts them to analog voltages via DAC, avoiding real-time computational complexity while maintaining high resolution and eliminating switching artifacts through smooth analog output.

Inventive Principle:

Principle #10Preliminary action

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 achieves high accuracy and flexibility in generating complex waveforms, reducing temperature dependencies and manufacturing costs, while maintaining analog sound quality and precision, enabling a wide range of musical sounds and improved pitch stability.

Implementation Method 1

a capacitor is charged through a constant current source which is controlled by a control voltage and discharges upon reaching a predetermined charging potential, which results in an oscillation of a typically saw-tooth wave signal

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The exponential oscillator uses the exponential response of the current across the transistor as related to the input voltage across the base-emitter junction

Methodology Applied

Scientific EffectExponential response of transistor junction:

Data Source

PatentUS10229664B2Voltage controlled oscillator with variable core for electronic musical instrument and related methods

Publication Date: 2019.03.12 INMUSIC MMI ACQUISITION LLC

AI summary

A signal generator for a musical instrument includes a voltage-controlled oscillator (VCO) comprising a control voltage input and a VCO output. The control voltage input controls a frequency of the VCO output. A controller is configured to control the voltage-controlled oscillator by inputting a sequence of analog control voltages from a plurality of preloaded control voltage inputs.