Variable capacitance biasing device
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Solution Overview
Problem
Electronic circuits with variable capacitance, particularly voltage-controlled oscillators, suffer from temperature-dependent frequency variations that affect their operation, leading to phase-locked loop instability.
Innovation Solution
A device comprising a bandgap circuit and MOS transistors to generate temperature-stable bias voltages for variable capacitors, compensating for temperature effects by adjusting bias voltages based on temperature-dependent currents, thereby stabilizing the capacitance value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable capacitance is used in a voltage-controlled oscillator, then the frequency can be adjusted, but the frequency becomes dependent on temperature variations
Solution Approach 1:
The patent changes the voltage parameter applied to the variable capacitance to compensate for temperature effects. By adjusting the bias voltage across the variable capacitor based on temperature, the capacitance value is modified to counteract temperature-induced frequency drift, thereby maintaining frequency stability while preserving frequency adjustment capability
Solution Approach 2:
The patent implements a feedback mechanism where the temperature-dependent voltage is fed back to the variable capacitance. The circuit monitors temperature variations and automatically adjusts the capacitance bias voltage in response, creating a closed-loop system that stabilizes frequency against temperature changes
2Adaptability or versatility
If the capacitance value is varied to control frequency, then frequency tuning is achieved, but phase-locked loop stability deteriorates
Solution Approach 1:
The patent modifies the bias voltage parameter across the variable capacitance in a controlled manner. By changing the voltage level according to temperature rather than arbitrarily varying capacitance, the frequency tuning is achieved through a predictable parameter change that maintains phase-locked loop 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 solution reduces temperature-dependent frequency variations in voltage-controlled oscillators, enhancing phase-locked loop stability and frequency accuracy.
Implementation Method 1
a first bandgap circuit configured to apply a temperature-stable voltage across a first resistive element
Implementation Method 2
a second resistive element comprising one or more MOS transistors in series and each connected as a diode
Implementation Method 3
to provide a second current proportional to the absolute temperature
Data Source
Figure 1~3
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Figure 6~7
AI summary
The present description relates to a device (500). A first circuit (BG) provides a first current (Ibg) flowing in a first resistive element receiving a temperature-stable voltage, and a second current (Iptat) proportional to the temperature. A second resistive element (R) comprises MOS transistors (T) in series and in diode, and has a first terminal connected to a reference potential (GND) and a second terminal coupled to a supply potential (VDD). A second circuit (C1) provides, in the second resistive element (R), a copy (Ibgc1) of the first current (Ibg). A third circuit (C2) applies a voltage to a back gate (600) of the transistors (T), determined by the second current (Iptat).