PLL VCO Control Voltage Compensation Without Temperature Sensors

Solution Overview

Problem

Conventional PLL circuits face challenges in compensating for unwanted variations in the VCO control voltage due to factors like temperature variations and device degradation, requiring temperature sensors or complex capacitor adjustments, which are costly and inaccurate.

Innovation Solution

A phase-locked loop circuit with a digital logic circuit and a finite state machine (FSM) that compares the control voltage to a reference signal, iteratively adjusting a compensation signal to maintain the VCO control voltage at a desired level, independent of the variation's cause.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If temperature sensors or complex capacitor adjustments are used to compensate for VCO control voltage variations, then compensation accuracy is improved, but device complexity and cost increase

Engineering Contradiction:

Improvecompensation accuracyVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The PLL circuit performs self-compensation by using its own internal components (phase detector, charge pump, and existing control voltage node) to detect and correct control voltage variations. The phase detector compares the VCO output phase with the reference signal phase, and the charge pump automatically adjusts the control voltage to maintain lock, eliminating the need for external temperature sensors or complex adjustment mechanisms.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The existing phase detector and charge pump components, originally designed for phase locking functionality, are made to serve a dual purpose: maintaining phase lock and compensating for control voltage variations. This multi-functionality approach allows the same circuit elements to handle both primary PLL operation and temperature/drift compensation without adding separate dedicated compensation hardware.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If temperature sensors are used to compensate for control voltage variations, then compensation capability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvecompensation capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The PLL circuit performs self-compensation by using its own internal components (phase detector, charge pump, and existing control voltage node) to detect and correct control voltage variations. The phase detector compares the VCO output phase with the reference signal phase, and the charge pump automatically adjusts the control voltage to maintain lock, eliminating the need for external temperature sensors or complex adjustment mechanisms.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The existing phase detector and charge pump components, originally designed for phase locking functionality, are made to serve a dual purpose: maintaining phase lock and compensating for control voltage variations. This multi-functionality approach allows the same circuit elements to handle both primary PLL operation and temperature/drift compensation without adding separate dedicated compensation hardware.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If conventional PLL circuits operate with fixed control voltage, then circuit design is simplified, but output frequency stability deteriorates under temperature variations

Engineering Contradiction:

Improvecircuit design simplicityVSAvoidoutput frequency stability

Core Design Contradiction:

Device complexityVSStability of the object's composition

Solution Approach 1:

The PLL circuit uses feedback through the phase detector to continuously monitor the phase difference between the VCO output and reference signal. When control voltage variations cause frequency drift, the phase detector detects the resulting phase error and generates corrective signals through the charge pump to adjust the control voltage, automatically restoring frequency stability without complex design changes.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control voltage is transformed from a fixed static value to a dynamically adjustable parameter. The charge pump circuit enables the control voltage to automatically vary in response to phase errors, allowing the VCO frequency to adapt and track the reference frequency despite temperature variations or other disturbances affecting the control voltage.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12531717B2Phase-locked loop circuit and corresponding method of operation

Publication Date: 2026.01.20 STMICROELECTRONICS INT NV

AI summary

In a PLL, a VCO is controlled by a control voltage and produces an output periodic signal. A comparator compares the control voltage to a comparison signal, and asserts/de-asserts a detection signal if the control voltage is higher/lower than the comparison signal. A digital logic circuit receives the detection signal, produces the comparison signal, and produces a compensation signal to control the VCO. During a VCO compensation procedure first phase, the digital logic circuit determines and stores a value of the comparison signal that corresponds to a current value of the control voltage, and compares the stored value of the comparison signal to a target value to determine whether the control voltage needs to be increased or decreased. During a VCO compensation procedure second phase, the digital logic circuit iteratively changes the value of the compensation signal until the control voltage reaches a desired value.