MEMS Sensing Device Charge Pump Source Follower PGA PSRR
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Solution Overview
Problem
MEMS devices with single-ended source follower output face challenges in improving the power supply rejection ratio (PSRR) of the programmable gain amplifier (PGA), limiting their performance.
Innovation Solution
A sensing device is designed with a charge pump, a MEMS sensor, and a source follower connected to a PGA, which generates two-ended differential output voltages, enhancing the PSRR by utilizing a charge pump to provide a pump voltage and a source follower to generate reference and input voltages, and a PGA to produce two-ended output voltages based on these voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-ended source follower output is used in MEMS devices, then the device structure is simple, but the PSRR of the PGA cannot be improved
Solution Approach 1:
The source follower output is segmented into two separate outputs: a first output for the inverting input of the PGA and a second output for the non-inverting input. This segmentation allows independent optimization of each output path, enabling improved PSRR through differential signaling while maintaining manageable circuit complexity through modular design.
2Reliability
If a two-ended differential output is implemented in the source follower, then the PSRR of the PGA is improved, but the device complexity increases
Solution Approach 1:
The source follower circuit is designed to perform multiple functions simultaneously: it provides both single-ended and differential outputs from the same input stage, enables PSRR improvement through differential signaling, and maintains compatibility with existing single-ended PGA designs. This multi-functionality achieves PSRR enhancement without requiring complete redesign of the entire signal path.
Solution Approach 2:
The output configuration transitions from a single-dimensional (single-ended) output to a two-dimensional (differential) output structure. By adding the second output path and enabling differential signaling, the system achieves improved PSRR performance while the increased complexity is managed through systematic circuit design rather than random additions.
Data Source
AI summary
A sensing device comprises a charge pump, a MEMS sensor, a source follower and a PGA. The charge pump is configured to provide a pump voltage. The MEMS sensor is electrically connected to the charge pump and configured to generate an input voltage according to environment variations. The source follower is electrically connected to the MEMS sensor and configured to generate a followed reference voltage according to the pump voltage and to generate a followed input voltage according to the input voltage. The PGA has an input end of the PGA electrically connected to the source follower and is configured to generate two-ended differential output voltages outputted through a first output end and a second output end according to a difference between the followed reference voltage and the followed input voltage.