Differential Envelope Demodulator for Common-Mode Noise Rejection
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Solution Overview
Problem
Existing envelope detectors in isolated gate drivers fail to effectively reject common mode noise and power supply noise, leading to errors in control signals due to vulnerability to common mode transients and parasitic electrical parameters.
Innovation Solution
The proposed envelope detector employs multiple differential pairs of transistors, a resistor, a current source, and a comparator to determine peak values of input signals, rejecting common mode noise and power supply noise through differential pair topologies and filter configurations, which store peak values at drain terminals rather than source terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional envelope detectors are used in isolated gate drivers, then the circuit structure is simple, but the common mode rejection and power supply noise rejection are insufficient leading to control signal errors
Solution Approach 1:
The envelope detector is divided into multiple independent differential pairs (first and second differential pairs), each responsible for detecting specific signal components. This segmentation allows each pair to reject common mode noise independently while maintaining overall detection accuracy, resolving the contradiction between reliability and complexity.
Solution Approach 2:
Each differential pair is configured with specific local characteristics (transistor arrangements, resistor values, capacitor configurations) optimized for rejecting particular noise sources. The first differential pair targets common mode transients while the second targets power supply noise, providing localized quality improvements that collectively enhance overall reliability.
2Object-affected harmful factors
If differential pairs are used to reject common mode noise, then common mode rejection improves, but the circuit complexity increases due to additional components
Solution Approach 1:
Multiple differential pairs are merged into a single integrated envelope detector circuit sharing common components such as the current source, resistors, and capacitors. This merging approach achieves enhanced common mode rejection through the combined action of differential pairs while avoiding the complexity of completely separate circuits, as components are strategically shared across pairs.
3Measurement precision
If peak values are stored at drain terminals instead of source terminals, then power supply noise rejection improves, but the circuit configuration becomes more complex
Solution Approach 1:
The patent transitions from storing peak values at source terminals to storing them at drain terminals, representing a dimensional change in the circuit topology. This configuration change enables the filters to operate in a different electrical dimension where power supply noise is naturally rejected, improving measurement precision while the shared component structure manages the added complexity.
Data Source
AI summary
An envelope detector comprises a first differential transistor pair that receives first and second input signals, a second differential transistor pair that receives third and fourth input signals, a resistor, a current source, and a comparator. The first and second differential pairs each comprise two transistors having first current terminals coupled together and second current terminals coupled together. The resistor is coupled between the second current terminals of the first and second differential pairs. The current source has a first terminal coupled to the second terminal of the resistor and to second current terminals of the second differential pair and a second terminal configured to receive a negative supply voltage. The comparator has a negative input coupled to first current terminals of the first differential pair and a positive input coupled to first current terminals of the second differential pair.