Programmable Capacitor Array Control for MOSFET Off-State Linearity
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Solution Overview
Problem
Existing programmable capacitor arrays experience linearity degradation due to the non-linearity of MOSFET switches, particularly when they are in the off state, leading to distortion of input signals.
Innovation Solution
The implementation of control circuitry that periodically turns on and off the MOSFET switch, even when it is intended to be off, to charge the drain voltage to the source voltage, minimizing linearity degradation by preventing the turn-on of p-well or p-substrate diodes at high frequencies, and using logic to generate control signals for the gate of the MOSFET.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If MOSFET switches are used in programmable capacitor array, then the array can be programmed to load/unload capacitors, but the non-linearity of MOSFET in off state causes distortion of input signal
Solution Approach 1:
The patent applies periodic action by switching the MOSFET on and off at a frequency significantly higher than the input signal frequency. This periodic switching maintains the average drain voltage close to the source voltage, preventing the non-linear turn-on behavior of the MOSFET and its internal diodes from distorting the input signal, while still achieving the desired capacitor loading/unloading function.
Solution Approach 2:
The patent changes the operating parameters of the MOSFET by using high-frequency switching to alter its effective behavior. By operating the MOSFET in a rapidly switching regime rather than in static on/off states, the patent transforms the non-linear device into an effectively linear element for the input signal frequency, thereby reducing distortion while maintaining programmability.
2Productivity
If MOSFET is kept off to unload capacitor, then capacitor is removed from input, but linearity degradation occurs due to non-linearity of MOSFET
Solution Approach 1:
The patent uses periodic switching action to maintain the MOSFET in a dynamically controlled state even when the capacitor needs to be unloaded. The high-frequency switching prevents the MOSFET from settling into a static off state that would cause linearity degradation, while still achieving effective capacitor unloading for the input signal frequency.
Solution Approach 2:
The patent applies preliminary action by pre-charging the drain voltage to the source voltage through periodic switching before the input signal can cause non-linear effects. This preparatory voltage maintenance prevents the non-linear turn-on behavior of the MOSFET and its internal diodes, preserving linearity while achieving capacitor unloading.
3Manufacturing precision
If periodic switching is used to maintain drain voltage, then linearity is improved, but additional control circuitry is required
Solution Approach 1:
The patent applies self-service by using the existing control infrastructure of the programmable capacitor array to generate the periodic switching signal. The control circuitry that already exists for programming the capacitor array is utilized to also generate the high-frequency switching signal, eliminating the need for separate dedicated control circuitry and reducing overall device complexity.
Solution Approach 2:
The patent makes the existing control circuitry multi-functional by having it serve both the original programming function and the new periodic switching function. This universal utilization of control resources achieves the linearity improvement through periodic switching without adding dedicated control circuitry, thereby minimizing the increase in device complexity.
Data Source
AI summary
In one example embodiment, a programmable capacitor array is provided for low distortion and minimizing linearity degradation of an input (Vin) by utilizing control circuitry to switch on and off an array of MOSFET switches. The control circuitry turns on a MOSFET to load a capacitance on Vin and turns off the MOSFET to remove the capacitance from Vin in response to a Din control signal. When the intention is to load Vin with the capacitance, the MOSFET is left on continuously. When the intention is to remove or unload the capacitance from Vin, the MOSFET is primarily turned off, however, the MOSFET is still periodically turned on with appropriate voltage levels in response to a clock signal for periods of time when the loading of the capacitance on Vin is tolerable to the system, thereby ensuring minimal linearity degradation of Vin due to the programmable capacitor array system.