Silicon Microphone Logarithmic Amplifier for Wide Dynamic Range
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Solution Overview
Problem
Digital microphones face challenges in handling large input signal swings without degrading signal-to-noise ratio (SNR) due to programmable gain amplifier (PGA) clipping, which distorts the input signal and impacts performance.
Innovation Solution
A logarithmic amplifier system is implemented using multiple programmable gain amplifiers with different gains, each driving a summing circuit, providing a piecewise linear transfer function through switched capacitor or continuous-time resistor circuits, allowing for quasi-constant SNR and reduced system area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single programmable gain amplifier is used to handle wide signal swings, then the amplifier may clip and distort the signal, but using multiple amplifiers with different gains increases device complexity
Solution Approach 1:
The patent divides a single amplifier function into multiple parallel programmable gain amplifiers (PGAs) with different gain values. Each PGA handles a specific segment of the input signal range, preventing clipping and distortion while maintaining quasi-constant SNR across the full dynamic range. The summing circuit combines outputs from these segmented amplifier paths.
Solution Approach 2:
The system dynamically selects and weights different amplifier paths based on the input signal level. The summing circuit automatically adjusts the contribution of each PGA output according to the instantaneous signal amplitude, providing adaptive gain control that optimizes SNR for varying signal conditions without requiring manual intervention.
2Adaptability or versatility
If the input signal range is increased to handle wide signal swings, then the ADC integrated circuit area increases, but limiting the range causes clipping and distortion
Solution Approach 1:
The input signal range is segmented into multiple zones, each handled by a dedicated PGA with optimized gain for that range. This allows the ADC to operate over a reduced, fixed range while the parallel PGA paths collectively cover the full wide dynamic range, avoiding the need for a large-area ADC that could handle the entire range directly.
Solution Approach 2:
The system changes the gain parameter of different amplifier paths based on the input signal level. By dynamically adjusting which PGA paths are active and their respective gain values, the system maintains a constant, optimized input range for the ADC regardless of the overall input signal amplitude, thereby keeping the ADC area small while handling wide signal swings.
3Device complexity
If complex anti-logarithmic digital signal processing is used to linearize the output, then processing complexity increases, but simpler processing reduces linearity accuracy
Solution Approach 1:
The patent performs preliminary linearization in the analog domain through the carefully designed piecewise linear transfer function of the summing circuit. By pre-shaping the transfer function to approximate the desired logarithmic response with high accuracy, the system minimizes the burden on subsequent digital anti-logarithmic processing, reducing both computational complexity and processing time while maintaining linearity accuracy.
Data Source
Figure 1A~1B
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AI summary
A logarithmic amplifier includes programmable gain amplifiers each having a different gain, wherein an input of each of the programmable gain amplifiers is coupled to an input of the logarithmic amplifier; and a summing circuit having inputs coupled to a corresponding output of each of the programmable gain amplifiers and an output coupled to an output of the logarithmic amplifier, wherein the summing circuit generates a logarithmic transfer function having piecewise linear segments.