Microphone Amplifier Feedback Circuit for Higher PSRR
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Solution Overview
Problem
Microphone chips, particularly those with MEMS microphones, face challenges in maintaining a high power supply rejection ratio (PSRR) due to direct coupling of supply potential from the bond pad to the sensitive input terminal of the amplifier circuit, leading to audible distortion from supply changes, especially with small parasitic capacitors limiting PSRR.
Innovation Solution
An electric amplifier circuit with a differential amplifier and a charge supplying circuit that compensates for supply potential changes by providing a feedback path and adjusting the potential at the second input terminal of the differential amplifier, effectively decoupling supply changes from the sensitive input terminal, thereby improving PSRR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a direct coupling from the supply bond pad to the sensitive input terminal of the amplifier circuit is used to simplify the package construction and reduce cost, then the package becomes more compact and cost-optimized, but the power supply rejection ratio (PSRR) deteriorates due to supply potential changes coupling to the input terminal
Solution Approach 1:
A charge supplying circuit is introduced as an intermediary component between the supply bond pad and the sensitive input terminal. This circuit compensates for supply potential changes by providing counteracting charge to the feedback path, thereby preventing supply variations from reaching the input terminal while maintaining the direct physical coupling in the compact package
2Ease of manufacture
If the package is constructed compactly with direct coupling to reduce cost and improve integration, then manufacturing cost decreases and integration improves, but audible distortion increases due to supply changes affecting the input terminal
Solution Approach 1:
The charge supplying circuit operates by sensing supply potential changes and automatically providing compensating charge through the feedback path. This feedback mechanism dynamically counteracts supply variations, preventing them from causing audible distortion at the output while maintaining the cost-effective compact package structure
3Volume of moving object
If small parasitic capacitors are present in the circuit to reduce component size and improve integration, then device size decreases and integration improves, but the power supply rejection ratio is limited and PSRR performance deteriorates
Solution Approach 1:
Instead of relying on large parasitic capacitors to improve PSRR, the invention changes the approach by using an active charge supplying circuit that dynamically adjusts charge compensation based on supply potential changes. This allows maintaining small capacitor sizes while achieving high PSRR through active parameter adjustment rather than passive component sizing
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
The solution enhances the PSRR of the amplifier circuit, reducing the impact of supply potential changes on the input terminal and minimizing audible distortion, ensuring better audio quality even with uncontrolled supply voltages.
Implementation Method 1
The charge supplying circuit is configured to supply an amount of the charge to the feedback path in dependence on a change of the supply potential
Data Source
AI summary
An electric amplifier circuit for amplifying an output signal of a microphone comprises a supply input terminal (V10) to apply a supply potential (VDDA) for operating the electric amplifier circuit and a differential amplifier (110) having a first input terminal (E110a) for applying the output signal of the microphone (20), a second input terminal (E110b) and an output terminal (A110) for outputting an amplified output signal (OUT) of the microphone (20). A feedback path (FP) is provided between the output terminal (A110) of the differential amplifier (110) and the second input terminal (E110b) of the differential amplifier (110). A charge supplying circuit (120) is coupled to the feedback path (FP) to supply an amount of the charge to the feedback path (FP) in dependence on the supply potential (VDDA). The amount of charge supplied to the feedback path may be dependent on a change of the supply potential (VDDA).