Pulsed Signal Front End With Reduced Noise Bandwidth
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Solution Overview
Problem
Pulsed input systems, such as those used in pulse oximetry, face challenges in achieving low noise and low power consumption due to the need for high bandwidth transimpedance amplifiers, which result in high power consumption and increased noise output, especially when dealing with low duty cycle pulse inputs.
Innovation Solution
The implementation of a reduced noise bandwidth front end using a filter stage and a continuous time sigma delta ADC decouples ADC conversion speed from pulsed duty cycle timing, reducing power consumption and noise output by limiting the noise bandwidth and using a resistive load, thereby reducing the drive requirements of the front end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large bandwidth transimpedance amplifier is used to support pulsing input signals, then the signal bandwidth is improved, but the equivalent noise bandwidth increases and power consumption increases
Solution Approach 1:
The patent divides the bandwidth requirements into two separate stages: a first transimpedance amplifier with bandwidth matched to the pulse repetition frequency, and a second transimpedance amplifier with bandwidth matched to the lower signal bandwidth. This segmentation allows each stage to operate at its optimal bandwidth, preventing excessive noise integration while maintaining signal integrity.
Solution Approach 2:
The patent introduces an intermediary filtering stage between the photodetector and the second transimpedance amplifier. This filter acts as a mediator that limits the noise bandwidth before the signal reaches the second amplification stage, thereby reducing the equivalent noise bandwidth without compromising the signal bandwidth requirements.
2Speed
If a large bandwidth transimpedance amplifier is used to support pulsing input signals, then the signal bandwidth is improved, but the power consumption increases
Solution Approach 1:
The patent segments the amplification function into two separate transimpedance amplifier stages, each with bandwidth optimized for its specific function. The first amplifier handles the high-frequency pulse components, while the second amplifier processes the lower-frequency signal components. This segmentation reduces the total power consumption by avoiding the need for a single high-bandwidth amplifier to handle both frequency ranges simultaneously.
3Measurement precision
If the ADC conversion speed is coupled to pulsed duty cycle timing, then the signal processing accuracy is improved, but the power consumption increases
Solution Approach 1:
The patent implements dynamic bandwidth adjustment by using switches to selectively connect different transimpedance amplifier stages based on the input signal characteristics. During pulsing periods, the system dynamically switches between amplification stages to match the instantaneous bandwidth requirements, thereby reducing power consumption when full bandwidth is not needed while maintaining signal processing accuracy when required.
Data Source
AI summary
Embodiments of the invention provide a pulsed signal detection system with reduced noise bandwidth in the frontend. Analog to digital conversion speed is decoupled from the pulsed duty cycle timing. This in turn reduces the power consumption of the ADC and the front end while providing a high dynamic range. The ADC may be a continuous time sigma delta converter to reduce the drive requirements of the front end.