Switchable LC Tank Capacitance for Precise Discrete Frequency Control
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Solution Overview
Problem
Existing oscillation circuits, such as voltage-controlled oscillators, struggle to provide precise and discrete signal frequencies required in applications like mobile telephony to avoid interference, as they cannot effectively adjust capacitance to meet the needed frequency ranges.
Innovation Solution
An oscillator circuit with a discretely switchable capacitance module that uses a PMOS FET switch and DC feed circuits to selectively add or remove capacitance from the LC tank circuit, allowing for precise control of capacitance through control signals, thereby adjusting the resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a voltage-controlled oscillator uses a varactor to change capacitance, then the frequency can be shifted across a broad range, but the frequency control becomes continuous rather than precise and discrete
Solution Approach 1:
The patent divides the continuous capacitance adjustment into discrete segments by using multiple switchable capacitors (C1, C2, C3, etc.) that can be independently connected or disconnected from the LC tank circuit. Each capacitor represents a discrete capacitance step, allowing precise frequency control while maintaining broad frequency coverage through combination of different capacitor values.
Solution Approach 2:
The patent implements dynamic capacitance adjustment by using electronic switches (such as MOSFETs) controlled by digital control signals to connect or disconnect capacitors from the LC tank circuit in real-time. This allows the oscillator to dynamically shift between discrete frequency points based on digital input, combining the flexibility of continuous adjustment with the precision of discrete steps.
2Measurement precision
If discrete capacitance is added to the LC tank circuit, then precise frequency control is achieved, but the device complexity increases
Solution Approach 1:
The patent combines multiple switchable capacitors into a single integrated capacitance adjustment module that interfaces with the LC tank circuit through a unified control mechanism. The capacitors are connected in parallel configurations where their combined effect can be controlled by multiple control signals, reducing the overall complexity compared to independent control of each capacitor.
Solution Approach 2:
The patent designs the capacitance adjustment module to serve multiple functions: frequency synthesis, frequency multiplication, and frequency division. The same discrete capacitor bank can be controlled to achieve different frequency outcomes based on the control signal patterns, eliminating the need for separate circuits for different frequency control functions.
3Measurement precision
If switchable capacitors are connected in parallel with the tank circuit capacitor, then discrete capacitance adjustment is possible, but switching transients may interfere with the oscillation signal
Solution Approach 1:
The patent implements preliminary charging of the switchable capacitors through dedicated charge pumps or charge storage circuits before they are switched into the LC tank circuit. By pre-charging the capacitors to the appropriate voltage level, the switching action minimizes transient effects and voltage spikes that would otherwise interfere with the oscillation signal, allowing clean transitions between frequency states.
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
Enables precise and discrete adjustment of capacitance in the oscillator circuit, allowing for accurate frequency shifting and minimizing interference in wireless communication devices by allowing for the selective addition or removal of capacitance, thus enhancing frequency control.
Implementation Method 1
a capacitor coupled between a first node and a second node
Implementation Method 2
a tank circuit comprising an inductor and a capacitor
Implementation Method 3
a switch, having a control node, coupled between the second node and a third node
Data Source
AI summary
An oscillator circuit having a source of an oscillating signal, a tank circuit including an inductor and a capacitor, and a discretely switchable capacitance module configured to control an amount of capacitance in the oscillator circuit. The discretely switchable capacitance module includes, in one embodiment, a capacitor coupled between a first node and a second node, a switch, having a control node, coupled between the second node and a third node; and a DC feed circuit, having a first end coupled to the second node and a second end configured to receive a first or second control signal. The control node of the switch is tied to a predetermined bias voltage. When the first control signal is applied, the capacitor is coupled between the first node and the third node via the switch such that the capacitor is coupled in parallel with the capacitor of the tank circuit, and when the second control signal is applied the capacitor is decoupled from the tank circuit.