PDM Interface Multiplexing for Sensor Control
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Solution Overview
Problem
Current digital microphones, such as MEMS microphones, rely on pulse-density modulation (PDM) interfaces for signal transmission, which lack a control channel, making it impossible to adjust acoustic and electrical characteristics like sampling rate or sensitivity without increasing system cost and complexity.
Innovation Solution
A signal transmission architecture that integrates data and control interfaces using time division multiplexing, allowing sensed information and control information to be transmitted through a single interface, enabling configuration and adjustment of sensing devices without significant cost or complexity increases, by employing a mode switching circuit to activate the appropriate circuits based on clock, data, or power rail signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a PDM interface is used for signal transmission, then audio signal transmission is achieved, but control parameter adjustment capability is lost
Solution Approach 1:
The patent merges the control interface and data interface into a single PDM interface by time-division multiplexing. The mode switching circuit multiplexes between control mode (I2C/SPI/UART protocols) and data mode (PDM protocol) on the same physical interface, eliminating the need for separate control and data interfaces while maintaining both control parameter adjustment and audio signal transmission capabilities
Solution Approach 2:
The PDM interface is designed to serve multiple functions: it can transmit audio data in PDM mode and transmit control commands in I2C/SPI/UART modes. The mode switching circuit enables the interface to adapt its protocol based on the operation mode, making a single interface universal for both control and data transmission purposes
2Adaptability or versatility
If control channels are added to the PDM interface, then control parameter adjustment becomes possible, but system cost increases
Solution Approach 1:
The patent combines control and data transmission functions into the existing PDM interface without adding extra physical channels or pins. The mode switching circuit multiplexes control commands and audio data over the same physical interface, avoiding additional hardware costs while enabling control parameter adjustment capabilities
3Adaptability or versatility
If multiple transmission protocols are supported on a single interface, then adaptability improves, but circuit complexity increases
Solution Approach 1:
The mode switching circuit dynamically configures the interface protocol based on the operation mode. In control mode, it switches to I2C/SPI/UART protocols for parameter adjustment; in data mode, it switches to PDM protocol for audio transmission. This dynamic protocol adaptation enables multi-protocol support while containing circuit complexity through software-controlled switching rather than hardware multiplexing
Data Source
AI summary
A sensing device includes a sensed information transmitting circuit, a control information slave circuit and a mode switching circuit. The sensed information transmitting circuit converts sensed information into a transmission signal compliant with a signal format of a first transmission protocol. The control information slave circuit converts a received signal received from a signal transmission interface into control information according to a second transmission protocol, thereby to configure the sensing device. The mode switching circuit to activates one of the sensed information transmitting circuit and the control information slave circuit based on a signal on a clock channel of the signal transmission interface, a signal on a data channel of the signal transmission interface or a signal on a power rail of the sensing device, thereby to transmit or receive signals through the signal transmission interface.