Switching Amplifier Edge-Rate Control for Lower EMI
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Solution Overview
Problem
Switched-power circuits generate significant electromagnetic interference (EMI) due to varying power supply voltage, process, and temperature, which current control mechanisms fail to adequately address, exacerbating EMI generation.
Innovation Solution
A circuit and method that generates a reference output current with controlled dependence on power supply voltage, using first and second current references to stabilize edge rate against process and temperature variations, and adjusts current levels in a pre-driver stage to reduce EMI across varying power supply conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power supply voltage is increased to improve power output capability, then the power output capability is improved, but the electromagnetic interference (EMI) increases due to higher voltage switching
Solution Approach 1:
The patent implements dynamic edge rate control where the pre-driver current is adjusted in real-time based on the instantaneous power supply voltage level. As voltage increases, the edge rate is reduced dynamically, and vice versa. This dynamic adaptation allows the system to maintain high power output capability while continuously optimizing EMI performance according to operating conditions.
Solution Approach 2:
The patent changes the edge rate parameter as a function of power supply voltage. By establishing a controlled relationship where edge rate decreases with increasing voltage, the system transforms the fixed parameter approach into a variable parameter approach. This parameter transformation resolves the contradiction by allowing high voltage operation (for power) while maintaining controlled edge rates (for EMI reduction).
2Object-generated harmful factors
If the edge rate is reduced to decrease electromagnetic interference, then the electromagnetic interference is reduced, but the power delivery speed and efficiency deteriorate
Solution Approach 1:
The system dynamically adjusts edge rate based on actual operating conditions rather than using a fixed reduced edge rate. When power supply voltage is low, the edge rate can be higher to maintain power delivery speed. When voltage is high, the edge rate is reduced to control EMI. This dynamic behavior resolves the contradiction by optimizing both EMI and power delivery speed according to real-time conditions.
Solution Approach 2:
The patent establishes a voltage-dependent edge rate parameter relationship where the edge rate is not fixed but varies with power supply voltage. This parameter change strategy allows the system to achieve low EMI at high voltages while maintaining acceptable power delivery speed at low voltages, resolving the trade-off between EMI reduction and productivity.
3Reliability
If the pre-driver current is increased to improve edge rate control, then the edge rate control is improved, but the sensitivity to process and temperature variations increases
Solution Approach 1:
The patent implements a feedback mechanism where the power supply voltage level is sensed and used to adjust the pre-driver current accordingly. This closed-loop control compensates for process and temperature variations by adapting the control parameters based on actual operating conditions. The feedback approach improves reliability while reducing sensitivity to PVT variations through adaptive compensation.
Solution Approach 2:
The system uses the power supply voltage itself as the control signal for adjusting pre-driver current, creating a self-regulating mechanism. The voltage level automatically determines the appropriate edge rate control without requiring external sensing or complex compensation circuits. This self-service approach improves reliability while minimizing sensitivity to process and temperature variations.
Data Source
AI summary
Techniques for reducing electromagnetic interference (EMI) in a switching amplifier circuit, control edge-rate with reduced sensitivity to process and temperature variations and that is reduced with increasing power supply voltage. The techniques control current levels in a pre-driver stage that drives an output driver of a switching amplifier circuit, according to a bias control. A first slope of a variation of the bias control with respect to a power supply voltage of the switching amplifier circuit over a first portion of a range of variation of the power supply voltage has a direction opposite a second slope of the variation of the reference output current with respect to the power supply voltage over a second portion of the range of variation of the power supply voltage. The resulting operation reduces electromagnetic interference generated by the driver over the second portion of the range of variation of the power supply voltage.