Silicon Microphone Differential Converter for PGA Noise Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Single-ended silicon microphone signals face challenges in achieving good power supply rejection and signal-to-noise ratio due to noise generated in the programmable gain amplifier (PGA) of digital microphones.
Innovation Solution
A single-ended to differential converter is implemented using a non-inverting amplifier, an inverting amplifier, a charge pump with a charge pump output capacitor, and a feedback capacitor, which converts single-ended signals to differential signals, effectively canceling out noise and improving noise performance by maximizing PGA gain near the input pin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-ended PGA is used in digital microphones, then the device complexity is reduced, but the signal-to-noise ratio deteriorates due to noise generated in the PGA
Solution Approach 1:
The single-ended signal path is segmented into two separate differential paths. The input signal is distributed to both non-inverting and inverting amplifiers, which process the signal independently and then combine their outputs. This segmentation allows noise to be distributed and canceled across the two paths, improving the signal-to-noise ratio while maintaining relatively simple device architecture.
Solution Approach 2:
A charge pump circuit is introduced as an intermediary mechanism to generate the necessary differential voltages and drive the capacitive loads. The charge pump includes a charge pump output capacitor coupled between the second converter output and an internal node, and a feedback capacitor coupled between the first converter output and the internal node. This intermediary circuit enables effective noise cancellation by creating correlated noise paths that can be subtracted at the differential output.
2Measurement precision
If PGA gain is increased to improve signal-to-noise ratio, then the signal-to-noise ratio improves, but power supply rejection deteriorates due to increased sensitivity to power supply noise
Solution Approach 1:
The amplification function is segmented into two independent amplifier paths (non-inverting and inverting) that process the signal in parallel. By distributing the gain across two paths rather than concentrating it in a single high-gain stage, the circuit achieves high overall gain while maintaining better power supply rejection. Each amplifier path can be optimized independently, and their differential combination cancels common-mode power supply noise.
Solution Approach 2:
The charge pump circuit incorporates feedback mechanisms where the charge pump output capacitor and feedback capacitor create correlated signal paths. The feedback arrangement ensures that power supply variations affecting both amplifier paths are detected and canceled through the differential output, thereby improving power supply rejection ratio while maintaining high gain.
3Object-affected harmful factors
If a differential converter is implemented with charge pump and feedback capacitors, then power supply rejection is improved, but the device complexity increases
Solution Approach 1:
The charge pump circuit serves multiple functions simultaneously: it generates the necessary differential voltages, drives the capacitive loads of the amplifier outputs, implements feedback for noise cancellation, and provides power supply rejection. By making this single circuit block multi-functional, the overall device complexity is minimized while achieving the desired power supply rejection performance.
Solution Approach 2:
The charge pump output capacitor and feedback capacitor are merged into a single integrated circuit structure that performs both charge pumping and feedback functions. Rather than using separate components for each function, the patent combines them into a unified circuit arrangement where the capacitors serve dual purposes, thereby reducing the total component count and simplifying the overall converter structure.
Data Source
AI summary
A single-ended to differential converter includes a converter input, a first converter output, a second converter output, and an internal node, wherein the first converter output and the second converter output comprise a differential output; a non-inverting amplifier having an input coupled to the converter input, and an output coupled to the first converter output; an inverting amplifier having an input coupled to the first converter output, and an output coupled to the second converter output; a charge pump having a charge pump output capacitor coupled between the second converter output and the internal node; and a feedback capacitor coupled between the first converter output and the internal node.