Capacitive Sensor Package Shield Circuit for Communication Noise
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Solution Overview
Problem
Capacitive sensor devices face interference issues due to parasitic capacitive coupling from digital communication protocols, leading to corruption of shield voltage and subsequent output signal noise, especially in low-power consumption devices with limited current capability and frequency bandwidth.
Innovation Solution
A compensation circuit integrated into the ASIC die generates a compensating charge of opposite polarity and similar magnitude to interference signals, which is injected into the shield to reduce interference and stabilize the shield voltage, thereby protecting the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low power consumption is implemented in capacitive sensor devices, then energy efficiency is improved, but susceptibility to parasitic capacitive coupling from digital communication signals increases
Solution Approach 1:
A compensation circuit is introduced as an intermediary between the digital communication signals and the shield voltage. This circuit detects interference on the shield and generates compensating signals to counteract the parasitic capacitive coupling, allowing the system to maintain low power consumption while protecting against interference through active compensation rather than passive shielding alone
Solution Approach 2:
The compensation circuit implements a feedback mechanism by continuously monitoring the shield voltage for interference signals and dynamically adjusting the compensation signal accordingly. This feedback loop enables the system to maintain shield voltage stability despite low power consumption constraints, as the compensation is applied only when interference is detected rather than through continuous high-power shielding
2Productivity
If digital communication signals are transmitted through package substrates and bond wires, then data communication capability is improved, but interference signals are imposed on the shield voltage
Solution Approach 1:
The compensation circuit serves as an intermediary that intercepts and counteracts interference signals before they can significantly affect the shield voltage. By placing this circuit between the communication pathways and the shield, the system maintains full digital communication capability while the compensation circuit neutralizes the harmful coupling effects
Solution Approach 2:
The compensation circuit converts the harmful interference signals into beneficial compensation signals. By detecting the interference on the shield and generating opposite-polarity signals through the compensation circuit, the system transforms the negative effect of digital communication coupling into a positive correction that actually improves shield voltage stability
3Object-affected harmful factors
If a shield surrounds the active sensing portion, then protection against interference is improved, but the shield voltage becomes susceptible to interference from communication signals
Solution Approach 1:
The compensation circuit implements feedback by continuously monitoring the shield voltage for interference and dynamically adjusting compensation signals to maintain stability. This feedback mechanism allows the shield to maintain its protective function while actively correcting voltage deviations caused by communication signal coupling
Solution Approach 2:
The compensation circuit generates counterweight signals that oppose and neutralize the interference signals on the shield voltage. By producing compensation signals with opposite polarity to the detected interference, the system maintains shield voltage stability while preserving the shield's protective function against external interference
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
This approach effectively reduces interference on the shield voltage, enhancing the robustness of the sensor package against data communication-induced noise and maintaining signal integrity, improving overall performance.
Implementation Method 1
susceptibility to parasitic capacitive coupling from digital communication signals
Implementation Method 2
a voltage regulator configured to produce a shield voltage and a compensation circuit configured to produce a compensation signal
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
A sensor package (120) includes a first die (22) having a capacitor sensor that includes an active sensing portion (26) and a shield (28) surrounding the active sensing portion. The sensor package further includes a second die (24) that includes a voltage regulator (34) configured to produce a shield voltage (74) and a compensation circuit (128) configured to produce a compensation signal (130). The voltage regulator and the compensation circuit are electrically coupled to the shield. The voltage regulator is configured to regulate the shield to the shield voltage and the compensation signal produced by the compensation circuit is configured to reduce an interference signal (132, 134) on the shield voltage. The compensation circuit includes one or more coupling capacitors (142, 154) that may be programmable capacitor arrays and calibration methodology entails selecting capacitance values for the programmable capacitor arrays that minimizes the error on an output signal (72) of the sensor package (120).