Capacitor Array Switching for Faster Oscillator Settling
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Solution Overview
Problem
Existing touch sensing devices face challenges in accurately detecting frequency changes due to long settling times, which result in reduced sensitivity, especially at the initial stage of operation, because of the large time constant caused by high resistance values when switch elements are in the OFF state.
Innovation Solution
A capacitor circuit design that includes a parallel array of capacitors with select switches connected in series and short switches connected in parallel, where the short switches equalize the potential at the capacitor ends when the select switches are OFF, reducing the discharge time and settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switch elements are used in series with capacitors to perform ON/OFF operations, then capacitor selection and disconnection are enabled, but the large resistance value in the OFF state creates a large time constant that increases settling time
Solution Approach 1:
A short switch circuit is introduced as an intermediary component connected in parallel with each capacitor. This short switch acts as a mediator that provides an alternative discharge path for the capacitor, bypassing the high-resistance select switch when in the OFF state. The short switch circuit includes a switch element and a resistor that work together to create a controlled discharge path, enabling the capacitor to discharge quickly without being constrained by the select switch's high resistance value.
Solution Approach 2:
The resistance value in the discharge path is dynamically changed by switching between two different configurations: when the select switch is ON, the capacitor is connected to the inductor circuit through the low-resistance select switch; when the select switch is OFF, the short switch circuit activates to provide a low-resistance discharge path through its resistor. This parameter change in resistance allows the time constant to be adjusted, enabling fast discharge and reducing settling time.
2Stability of the object's composition
If the settling time is increased to ensure stable frequency, then frequency stability is improved, but the touch sensing device cannot accurately detect frequency changes at the initial stage of operation
Solution Approach 1:
The short switch circuit is activated in advance during the initial operation phase to quickly discharge any residual charge from the capacitors. This preliminary action of forced discharge ensures that the capacitors start from a known zero-state condition, enabling the oscillator to reach its steady-state frequency rapidly. This allows the touch sensing device to perform accurate frequency detection at the initial stage without waiting for an extended settling period.
3Reliability
If switch elements have high resistance in the OFF state to prevent leakage, then isolation is improved, but the time constant becomes large and discharge time increases
Solution Approach 1:
The discharge function is segmented from the select switch by introducing a separate short switch circuit. The select switch maintains its high resistance in the OFF state to ensure proper isolation and prevent leakage, while the short switch circuit handles the discharge function through its dedicated low-resistance path. This segmentation allows each component to optimize its specific function without compromising the other.
Data Source
AI summary
A capacitor circuit includes a capacitor array including first to n-th capacitors connected to each other in parallel; a select switch circuit including first to n-th select switches connected to the first to n-th capacitors in series, respectively; and a short switch circuit including first to n-th short switches connected to the first to n-th capacitors in parallel, respectively, and operating complementarily to the first to n-th select switches, respectively, wherein n is an integer of 2 or greater.