Biasing device for variable capacitance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electronic circuits with variable capacitors, particularly voltage-controlled oscillators, suffer from temperature-dependent frequency variations that affect their operation, leading to locking issues in phase-locked loops.
Innovation Solution
A biasing device comprising a bandgap circuit and MOS transistors to generate temperature-stable and temperature-dependent bias voltages for variable capacitors, compensating for temperature variations by adjusting the capacitance value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable capacitor is used in a voltage-controlled oscillator, then the oscillator frequency can be tuned, but the frequency becomes dependent on temperature variations
Solution Approach 1:
The patent changes the electrical parameters (voltages and currents) applied to the variable capacitor by introducing temperature-dependent bias voltages. The bandgap circuit generates reference voltages that are used to control the capacitance value of the variable capacitor, thereby compensating for temperature-induced frequency drift in the voltage-controlled oscillator.
2Reliability
If temperature compensation is implemented using additional circuits, then frequency stability improves, but device complexity increases
Solution Approach 1:
The bandgap circuit serves multiple functions: it generates stable reference voltages for biasing the variable capacitor, provides temperature compensation signals, and establishes current references for the oscillator circuit. This multi-functionality reduces the need for separate dedicated compensation circuits, thereby limiting the increase in overall device complexity while achieving frequency stability.
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 device stabilizes the frequency of voltage-controlled oscillators by minimizing temperature-dependent frequency shifts, ensuring reliable operation across varying temperatures.
Implementation Method 1
a first bandgap circuit configured to apply a temperature-stable voltage across a first resistive element so that a first current flows therethrough, and to deliver a second current proportional to absolute temperature
Implementation Method 2
a second resistive element comprising one or a plurality of MOS transistors in series and each connected as a diode
Implementation Method 3
apply the first control voltage to a back gate of the transistors of the resistive element
Data Source
AI summary
A biasing device for variable capacitance is provided. An example device comprises a first circuit. The first circuit delivers a first current flowing through a first resistive element receiving a temperature-stable voltage, and a second current proportional to temperature. A second resistive element comprises MOS transistors in series and connected as a diode, and has a first terminal connected to a reference potential and a second terminal coupled to a power supply potential. A second circuit delivers, in the second resistive element, a copy of the first current. A third circuit applies a voltage to a back gate of the transistors, determined by the second current.