Microphone Circuit Noise Suppression via Reset Node Clamping
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Solution Overview
Problem
Conventional microphone circuits generate a significant popping noise during reset due to temporary voltage increases, which degrade performance and require a long converge period to settle, affecting sound pressure levels and circuit stability.
Innovation Solution
Incorporating a switch circuit between the microphone circuit's node and ground, which is activated during reset to clamp the voltage to ground, preventing the popping noise by coupling the node to ground only during the reset period when the biasing voltage is applied, and decoupling it once the voltage status stabilizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a biasing voltage is applied to the pre-amplifier during reset, then the pre-amplifier can be initialized and powered up, but a temporary voltage increase occurs at the node causing popping noise
Solution Approach 1:
The switch circuit is activated before the biasing voltage is fully applied to the pre-amplifier, preemptively coupling the node to ground. This preliminary action prevents the temporary voltage increase from occurring in the first place, thereby eliminating the popping noise while still allowing the pre-amplifier to initialize properly.
Solution Approach 2:
The switch circuit acts as an intermediary element between the node and ground, controlling the coupling state based on the reset signal. During reset, the switch circuit mediates by providing a low-impedance path to ground, preventing voltage transients. After reset, it decouples to allow normal signal processing.
2Object-generated harmful factors
If the node is left floating during reset, then no popping noise is generated, but the voltage status remains unstable and requires a long converge period
Solution Approach 1:
The switch circuit provides a preliminary low-impedance path to ground before the biasing voltage is applied, preemptively establishing a stable voltage reference. This prevents the node from floating and eliminates the need for a long converge period, reducing the stabilization time while preventing popping noise.
3Object-generated harmful factors
If the switch circuit is always on, then the node is always clamped to ground preventing popping noise, but the microphone circuit cannot function properly during normal operation
Solution Approach 1:
The switch circuit is designed to be dynamically controlled by the reset signal, changing its state based on operational requirements. During reset, it is on to clamp the node to ground and prevent popping noise. During normal operation, it is off to allow the microphone circuit to function properly. This dynamic switching resolves the contradiction between noise prevention and circuit functionality.
Data Source
AI summary
The invention provides a microphone circuit. In one embodiment, the microphone circuit comprises a transducer, a biasing resistor, a pre-amplifier, and a switch circuit. The transducer is coupled between a ground and a first node for converting a sound into a voltage signal output to the first node. The biasing resistor is coupled between the ground and the first node. The pre-amplifier is biased with a biasing voltage and coupled between the first node and a second node, and amplifies the voltage signal to obtain an output signal at the second node. The switch circuit is coupled between the first node and the ground, couples the first node to the ground when the microphone circuit is reset, and decouples the first node from the ground after a voltage status of the microphone circuit is stable, thus clamping a voltage of the first node to the ground to prevent generation of a popping noise when the microphone circuit is reset.