Interpolative Divider VCXO for Multi-Output Clock Control

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Solution Overview

Problem

Existing solutions for voltage-controlled oscillators (VCXOs) face challenges in cost, size, and reliability due to the need for multiple crystal oscillators and phase-locked loops (PLLs) with LC oscillators, which result in increased silicon area and power consumption, as well as signal crosstalk issues when multiple oscillators operate at close frequencies.

Innovation Solution

The use of a reference clock generator and interpolative dividers, coupled with phase interpolators and delta sigma modulators, allows for the generation of multiple independent output frequencies using a single PLL, reducing the need for multiple PLLs and minimizing silicon area while eliminating crosstalk by using a single reference clock signal and arithmetic combination of divide ratios with digital voltage control signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple crystal oscillators are used to provide multiple VCXOs, then multiple independent frequency outputs are achieved, but cost, size, and reliability deteriorate

Engineering Contradiction:

Improvemultiple independent frequency outputsVSAvoidsystem reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent merges multiple VCXO functions into a single integrated circuit that uses one crystal oscillator and multiple interpolative dividers. This consolidation eliminates the need for multiple separate crystal oscillators, thereby improving reliability while maintaining the capability to provide multiple independent frequency outputs through digital control of the interpolative dividers.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The single VCXO circuit is designed to perform multiple functions by generating multiple frequency outputs through interpolative dividers. The circuit can be configured to provide different frequency outputs simultaneously or independently, making it a universal solution that replaces multiple dedicated oscillators.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If multiple PLLs with LC oscillators are used to provide VCXO functionality, then frequency control flexibility is improved, but silicon area and power consumption increase

Engineering Contradiction:

Improvefrequency control flexibilityVSAvoidsilicon area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent combines the functionality of multiple PLLs with LC oscillators into a single VCXO circuit that uses one crystal oscillator and multiple interpolative dividers. This merging dramatically reduces silicon area while maintaining frequency control flexibility through digital manipulation of the interpolative dividers.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent replaces the mechanical/LC oscillator-based frequency generation with a digital approach using interpolative dividers. By substituting the LC resonance mechanism with digital frequency division and interpolation, the circuit achieves comparable frequency control flexibility with significantly reduced silicon area and power consumption.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If multiple LC oscillators with close frequencies are placed on the same die, then multiple frequency outputs are achieved, but signal crosstalk increases

Engineering Contradiction:

Improvemultiple frequency outputsVSAvoidsignal crosstalk

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent merges multiple frequency generation functions into a single oscillator circuit with multiple interpolative dividers. This eliminates the need for multiple LC oscillators operating at close frequencies, thereby removing the source of signal crosstalk while still providing multiple frequency outputs through digital control.

Inventive Principle:

Principle #5Merging (Combining)

4Adaptability or versatility

If multiple crystal oscillators are used to provide multiple VCXOs, then multiple independent frequency outputs are achieved, but device complexity increases

Engineering Contradiction:

Improvemultiple independent frequency outputsVSAvoidoscillator circuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent merges multiple VCXO circuits into a single integrated structure that shares a common crystal oscillator and uses interpolative dividers for frequency multiplication. This consolidation reduces device complexity by eliminating redundant oscillator circuits while maintaining the capability to provide multiple independent frequency outputs through digital control of the dividers.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS8248175B2Oscillator with external voltage control and interpolative divider in the output path

Publication Date: 2012.08.21 SKYWORKS SOLUTIONS INC

AI summary

An oscillator output is controlled from an external voltage control terminal using an interpolative divider as a frequency modulator. The oscillator includes a reference clock generator, analog to digital converter, and an interpolative divider. Nominal output frequency is determined by the frequency of the reference clock and the nominal divide value of the interpolative divider. The divide value is changed according to the voltage control input value which is converted to a digital value via an analog to digital converter. Multiple interpolative dividers may be coupled to the single reference clock generator and each have a voltage control input and analog to digital converter.