Oversampled Microphone Fractional Delay for Distortion-Free Beamforming
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Solution Overview
Problem
Existing digital microphone systems face challenges in interfacing analog signals with digital electronics, particularly in introducing a fractional time delay in the oversampled domain without disturbing the circuitry or impacting the Application Processor.
Innovation Solution
A programmable fractional time delay is introduced in the oversampled domain using a Fractional Delay Block, which receives the oversampled output from the PDM modulator and applies a time delay that is a fraction of a baseband clock period, programmable from 0 to 512 delay elements, using control logic and bidirectional I/O to manage the clock and L/R pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a fractional time delay is introduced using traditional FIR filters, then time delay is achieved, but distortion is incurred
Solution Approach 1:
The patent changes the fundamental parameter of time delay implementation from filter-based (FIR) to domain-based (oversampled). By operating in the oversampled domain where sampling frequency is much higher than baseband frequency, the system achieves fractional time delay as integer delays at the higher sampling rate, eliminating the distortion inherent in traditional FIR filter approaches.
2Adaptability or versatility
If fractional time delay is implemented in the oversampled domain, then flexibility and precision are improved, but device complexity increases
Solution Approach 1:
The patent introduces an intermediary oversampled domain as a buffer between the analog input and baseband processing. This intermediary domain with higher sampling frequency enables precise fractional time delays to be implemented as simple integer delays, providing flexibility without requiring complex filter circuits in the baseband domain.
Solution Approach 2:
The time delay function is segmented into the oversampled domain where it can be implemented as simple buffer delays. The complex signal processing is separated from the time delay function, allowing each to be optimized independently - the oversampled domain handles timing precision while baseband handling achieves signal processing.
3Ease of operation
If existing system bus and Application Processor are used without modification, then ease of operation is maintained, but adaptability to fractional time delay is limited
Solution Approach 1:
The patent adds another dimension - the oversampled domain - to the existing system architecture. Instead of modifying the baseband domain where the Application Processor operates, the invention introduces time delay control in the oversampled domain, allowing fractional delays while maintaining compatibility with existing baseband processing infrastructure.
Data Source
AI summary
An apparatus to time delay a digital, signal output from an oversampled sensor includes a first time delay element and a second time delay element. The first time delay element has a first input and a first output. The first time delay element is configured to output a time delayed signal that is time delayed by an integer number of sampling clock cycles. An output of the oversampled sensor is connected to the first input of the first time delay element. The second time delay element has a second input and a second output and is configured to output a time delayed signal that is time delayed by an integer number of sampling clock cycles. The first output of the first time delay element is connected to the second input of the second time delay element. A multiplexer has a control input and a multiplexer output. The first output of the first time delay element is connected to a first multiplexer input. The second output of the second time delay element is connected to a second multiplexer input. In operation, time delay information is used to provide a signal to the control input to select a particular multiplexer input for output on the multiplexer output. The output of the oversampled sensor is time delayed by an amount provided by the particular multiplexer input.