Switching Regulator Noise Immunity via Current Mirror
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Solution Overview
Problem
Conventional switching regulators face challenges in maintaining output accuracy in noisy environments due to susceptibility to noise in current mode control, while increasing the sense resistor resistance to improve signal-to-noise ratio leads to a loss in conversion efficiency.
Innovation Solution
A switching regulator design that generates a PWM signal by comparing an error voltage with a slope voltage, offsetting the voltage level based on a sense current, and using a sense resistor, sense current, slope current, and slope voltage generating means to achieve current mode control with improved noise resistance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sense resistor resistance is increased to improve the signal-to-noise ratio, then the output accuracy in noisy environments is improved, but the conversion efficiency of the switching regulator is reduced
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary between the sense resistor and the PWM control circuit. The current mirror circuit copies the sense current without requiring a large sense resistor, thereby providing noise immunity while maintaining low power loss. The current mirror acts as a mediator that transfers the sensing function without the harmful side effect of power dissipation associated with high resistance.
Solution Approach 2:
The patent replaces the direct voltage sensing method (which relies on Ohm's law V=IR and requires high R for noise immunity) with a current-based sensing method. By using a current mirror circuit to replicate the sense current, the system substitutes the mechanical/electrical relationship of voltage-proportional-to-resistance with a current-proportional-to-load relationship, eliminating the need for high resistance values.
2Speed
If current mode control is implemented by directly using the sense voltage, then the response speed to load fluctuations is improved, but the susceptibility to noise increases
Solution Approach 1:
The current mirror circuit serves as an intermediary that processes the sense current before it reaches the PWM control circuit. Instead of directly using the small sense voltage (which is noise-susceptible), the current mirror creates a replicated current signal that can be more easily processed and is less vulnerable to noise interference, while still maintaining fast response characteristics.
Solution Approach 2:
The patent transitions from voltage-domain sensing to current-domain sensing by using a current mirror circuit. This dimensional change from voltage to current allows the system to maintain fast response (inherently available in current mode control) while avoiding the noise susceptibility associated with small voltage signals. The current mirror operates in a different electrical domain that is more robust to noise.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances output accuracy in noisy environments without compromising conversion efficiency, reducing power consumption, and ensuring reliable operation in electronic devices like mobile telephones.
Implementation Method 1
a sense resistor for generating a sense voltage commensurate with a switch current flowing through the output transistor
Implementation Method 2
driving one end of an energy storage element (such as a capacitor or inductor) through the turning on and off of an output transistor
Data Source
AI summary
A switching regulator (20) includes a sense resistor (Rs), a sense current generating circuit (213) for generating a sense current (Isense) commensurate with a sense voltage (Vsense), a slope current generating circuit (214) for generating a slope current (Islope) with a ramped or triangular waveform, a slope voltage generating circuit (215) for generating a slope voltage (Vslope) commensurate with a summed current (Isense plus Islope), an error amplifier (ERR) for generating an error voltage (Verr) commensurate with an error of an output, a comparator (CMP) for comparing the error voltage (Verr) with the slope voltage (Vslope) to generate a PWM signal and a switching control section (CTRL) for turning on and off an output transistor (N1) based on the PWM signal.