Comparator Oscillator Circuit for Fast Miller Capacitance Control
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Solution Overview
Problem
The existing oscillator circuits using comparators fail to follow relatively high-frequency control signals due to the time required to charge and discharge the Miller capacitance between the gate and drain of the MOSFET amplifier and its gate capacitance.
Innovation Solution
An oscillator circuit with a charge-discharge control unit and an output control unit is implemented, which includes transistors and logic circuits to control the charge-discharge of the Miller capacitance and the output of the gain unit, allowing the comparator output to follow high-frequency control signals by optimizing the charge and discharge processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MOSFET amplifier is used in the gain unit of the comparator, then the oscillation amplitude can be maintained, but the circuit cannot follow high-frequency control signals due to Miller capacitance charging and discharging time
Solution Approach 1:
The patent applies preliminary action by pre-charging the Miller capacitance through a dedicated charge path controlled by the first control signal. When oscillation detection indicates the need for amplitude restoration, the control circuit activates the charge pump to rapidly replenish the Miller capacitance charge before it fully depletes, thereby maintaining the amplifier's gain and the circuit's ability to follow high-frequency control signals.
2Adaptability or versatility
If external resistor and capacitor are used to determine oscillation frequency, then the frequency can be adjusted, but the circuit response time is limited by capacitor charging and discharging
Solution Approach 1:
The patent introduces an intermediary charge pump circuit that mediates between the control signals and the Miller capacitance. This intermediary component provides a dedicated charge transfer path that operates independently of the external RC time constants, allowing frequency adjustment through control signal timing while maintaining fast response through direct charge pumping.
Data Source
AI summary
An oscillator circuit uses a comparator, and the oscillator circuit controls charge-discharge of the Miller capacitance between the gate and the drain of a MOSFET serving as an amplifier of the gain unit and the gate capacitance of the MOSFET, and enables the comparator output to follow a relatively high-frequency control signal that is input externally. The oscillator circuit uses a comparator having a differential unit and a gain unit. The oscillator circuit includes a charge-discharge control unit that connects to the output of the differential unit and is configured to control charge-discharge of the Miller capacitance between the gate and the drain of a MOSFET (N2) serving as an amplifier of the gain unit and the gate capacitance of the MOSFET, and an output control unit configured to control the output of the gain unit.