Programmable VCO Calibration for Stable PLL Frequency and Gain

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Solution Overview

Problem

Voltage-controlled oscillators in phase-locked loops face instability due to fluctuations in supply voltage and temperature, which existing self-calibrating methods fail to address effectively by independently calibrating center frequency and gain.

Innovation Solution

A programmable voltage-controlled oscillator with a trimming circuit that adjusts center frequency and gain separately before normal operation, using a digital-to-analog converter and voltage-to-current converter to generate currents based on programming codes, allowing for independent adjustment of center frequency and gain.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a voltage-controlled oscillator is used in a phase-locked loop, then the oscillator can generate periodic signals with adjustable frequency, but the oscillator performance deviates due to supply voltage fluctuations and temperature changes

Engineering Contradiction:

Improvefrequency adjustment capabilityVSAvoidoperational stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies preliminary action by performing calibration of the VCO before normal operation. A calibration mode is activated where a calibration signal replaces the reference signal, and the control voltage is adjusted to match a target frequency. This preliminary calibration establishes accurate center frequency and gain characteristics before the PLL enters normal operation, compensating for process, temperature, and supply voltage variations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes physical parameters by introducing a calibration signal with known characteristics and adjusting the control voltage to a calibration value that produces a target frequency. The calibration process modifies the operating parameters (center frequency and gain) of the VCO to compensate for environmental variations, thereby improving reliability while maintaining frequency adjustability.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If self-calibrating methods are used to adjust the oscillator, then the center frequency can be corrected, but the gain remains uncalibrated and independently adjustable

Engineering Contradiction:

Improvecenter frequency accuracyVSAvoidcalibration completeness

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the calibration process into two distinct phases: center frequency calibration and gain calibration. During center frequency calibration, the control voltage is adjusted to match the target frequency. During gain calibration, the control voltage is adjusted to match the target gain while maintaining the calibrated center frequency. This segmentation ensures both parameters are independently calibrated without interfering with each other, achieving complete calibration without excessive complexity.

Inventive Principle:

Principle #1Segmentation

3Reliability

If the oscillator is calibrated before normal operation, then the desired characteristic curve can be achieved, but additional calibration time and steps are required

Engineering Contradiction:

Improvecharacteristic curve accuracyVSAvoidcalibration time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The calibration is performed as a preliminary action during manufacturing or initial setup, before the PLL enters normal operation. The calibration mode is activated once, the control voltage is adjusted to achieve the desired center frequency and gain, and then the calibration is complete. This preliminary calibration ensures accurate characteristic curves for the entire operational lifetime of the device, requiring calibration time only once rather than continuously.

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

This approach enhances the stability of phase-locked loops under changing conditions by ensuring the voltage-controlled oscillator maintains a desired characteristic curve, improving operational stability and performance.

Implementation Method 1

The trimming circuit comprises a first programmable component and a second programmable component. The first programmable component is configured to generate a first current according to the first programming code

Methodology Applied

Scientific EffectDigital-to-analog conversion:

Implementation Method 2

the second programmable component comprises a voltage-to-current converter

Methodology Applied

Scientific EffectVoltage-to-current conversion:

Data Source

PatentUS10833686B2Programmable VCO, method of calibrating the VCO, PLL circuit with programmable VCO, and setup method for the PLL circuit

Publication Date: 2020.11.10 AUSTRIAMICROSYSTEMS AG

AI summary

The PLL circuit comprises a phase/frequency detector (302), a loop filter (304, 306), a VCO (308) and a feedback loop (320). The VCO can be electrically disconnected from the PLL and comprises a programmable trimming circuit (316) and a current-controlled oscillator (318). For calibration the VCO is electrically disconnected from the loop filter and from the feedback loop, a constant reference voltage is applied to the voltage input (IN), a center frequency programming code (L) is applied to the trimming circuit, the center frequency programming code is iteratively adjusted until a desired center frequency is obtained, a gain programming code (K) is applied to the trimming circuit while the adjusted code is still applied, and the gain programming code is iteratively adjusted until a desired gain is obtained. Then the VCO is connected to the PLL, which is then ready for normal operation.