MEMS Transducer Package RLC Filter Circuit RF Noise
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Solution Overview
Problem
MEMS transducers, such as microphones, in portable devices face issues with RF noise interference due to their proximity to antennas, leading to audible noise and challenges in filter circuit design, particularly with traditional low pass RC filters that affect DC and low-frequency performance and output impedance.
Innovation Solution
A MEMS transducer package with a filter circuit comprising a resistor, capacitor, and inductor, where at least part of the filter circuit is integrated within an IPD chip, with the inductor provided in parallel with the resistor and the capacitor connected to a shared node, optimizing RF filtering while minimizing impact on audible frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a traditional low pass RC filter circuit is used with a resistor in series with the pin, then RF signals can be filtered, but the resistor limits the maximum current that can be provided to the part and adds to the output impedance of the analogue microphone
Solution Approach 1:
The patent changes the electrical parameters of the filter circuit by replacing the simple RC configuration with an RLC circuit where the inductor is connected in parallel with the resistor. This parameter change allows the circuit to achieve RF filtering while maintaining low output impedance and high current capability at audio frequencies, as the inductor provides a low-impedance path that bypasses the resistor for low-frequency signals.
2Object-affected harmful factors
If the resistor value is increased to improve RF filtering, then RF noise filtering is enhanced, but the maximum current that can be provided to the part is reduced and trimming becomes affected
Solution Approach 1:
The patent modifies the filter circuit parameters by adding an inductor in parallel with the resistor. This allows the use of higher resistor values for improved RF filtering without negatively impacting current provision or trimming operations, because the inductor provides an alternative low-impedance path for low-frequency currents during manufacturing and trimming processes.
3Object-affected harmful factors
If the resistor value is increased to improve RF filtering, then RF noise filtering is enhanced, but the output impedance of the analogue microphone increases, limiting ASIC design choices and increasing tolerance
Solution Approach 1:
The patent changes the filter circuit configuration to an RLC circuit with parallel inductor and resistor. This parameter change enables the output impedance to be maintained at low values across the audio bandwidth while still achieving effective RF filtering, thereby preserving ASIC design flexibility and meeting output impedance specifications with appropriate tolerance.
4Object-affected harmful factors
If a filter circuit is added to the transducer package, then RF noise filtering is improved, but the device complexity increases
Solution Approach 1:
The patent combines multiple filter components (resistor, capacitor, and inductor) into a single integrated RLC filter circuit within the transducer package. This merging of components achieves comprehensive RF noise filtering while minimizing the increase in device complexity through integrated implementation rather than separate discrete components.
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 configuration effectively filters RF noise without adding resistance at low frequencies, enhancing microphone performance and providing greater design flexibility and improved power supply rejection.
Implementation Method 1
an inductor L1 electrically connected in parallel with the resistor R1; and a capacitor C1 electrically connected to a node shared by the inductor L1 and the resistor R1
Implementation Method 2
a capacitor C1 electrically connected to a node shared by the inductor L1 and the resistor R1
Data Source
AI summary
A MEMS transducer package comprising a substrate; a filter circuit for filtering RF signals, the filter circuit comprising a resistor and a capacitor; and an IPD chip; wherein at least a portion of the filter circuit is provided within the IPD chip.