Microphone Amplifier Circuit Layout for Parasitic Capacitance Shielding
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Solution Overview
Problem
The existing microphone amplifying circuits suffer from a reduced signal-to-noise ratio due to the parasitic capacitor formed between the welding plate and the integrated circuit substrate, which causes voltage division and reduces the input signal amplitude.
Innovation Solution
A layer of underlying metal is introduced between the welding plate and the integrated circuit substrate to shield the parasitic capacitance, forming new parasitic capacitors. The underlying metal is connected to a circuit point that satisfies specific conditions, ensuring that the signals at both ends of the first parasitic capacitor are in the same phase and the gain is greater than or equal to 0.8, thereby eliminating the load effect on the microphone input end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a welding plate is used to connect the microphone to the integrated circuit substrate, then the microphone can be mounted and electrically connected, but a parasitic capacitor is formed between the welding plate and substrate that reduces the signal-to-noise ratio
Solution Approach 1:
An underlying metal layer is introduced as an intermediary between the welding plate and the substrate. This metal layer acts as a shield that redistributes the electric field, preventing the formation of a large parasitic capacitor between the welding plate and substrate, thereby maintaining connection reliability while reducing the harmful parasitic capacitance effect.
Solution Approach 2:
The parasitic capacitor that forms between the welding plate and the underlying metal layer is converted into a beneficial element by connecting it to the amplifier's output. This transforms the harmful parasitic capacitance into a load capacitor that can be utilized by the amplifier circuit, improving the overall signal-to-noise ratio.
2Object-affected harmful factors
If the parasitic capacitor of the welding plate is reduced, then the signal-to-noise ratio improves, but the circuit design becomes more complex
Solution Approach 1:
The capacitance problem is segmented into two parts: a small parasitic capacitor between the welding plate and underlying metal layer, and a controlled capacitor between the underlying metal layer and substrate. This segmentation allows each capacitor to be managed separately, with the first being minimized and the second being utilized as a beneficial load capacitor.
Solution Approach 2:
The underlying metal layer serves multiple functions: it acts as a shield to reduce parasitic capacitance, provides a grounding path, and creates a controlled capacitor that can be used as a load for the amplifier. This multi-functionality reduces the need for additional components, simplifying the overall circuit design.
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 weakens or eliminates the influence of the parasitic capacitor on the signal-to-noise ratio, improving the overall performance of the microphone amplifying circuit by maintaining the input signal amplitude and ensuring sufficient driving capability at the output end.
Implementation Method 1
a first parasitic capacitor is formed between the welding plate and the underlying metal, and a second parasitic capacitor is formed between the underlying metal and the substrate
Data Source
AI summary
The present invention provides a microphone amplifying circuit including an amplifier, a bias resistor, an input end, an output end, a microphone capacitor, a first parasitic capacitor and a second parasitic capacitor. The first parasitic capacitor is connected to the input end, and the other end of the first parasitic capacitor is connected to the output end. The second parasitic capacitor is connected to the output end, and the other end of the second parasitic capacitor is grounded. The first parasitic capacitor and the second parasitic capacitor are formed after adding a layer of underlying metal between the substrate of the integrated circuit and the welding plate. Compared with the related art, the microphone amplifying circuit design method and the microphone amplifying circuit of the present invention have higher signal to noise ratio and better performance.