Digital Constant On-Time Controller Offset Cancellation
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Solution Overview
Problem
Constant on-time (COT) DC-to-DC converters experience output voltage offset errors due to analog ripple-based control schemes, degrading regulation performance.
Innovation Solution
A digital COT controller is introduced, comprising a current sensing circuit, semi-amplitude detector, DC voltage detector, and PWM generator, which senses energy storage, detects voltage amplitudes, and generates a switch control signal by subtracting reference signals from combined sense and DC voltages to cancel output voltage offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an analog ripple-based control scheme is used in a COT DC-to-DC converter, then the converter can operate with constant on-time control, but output voltage offset error is introduced which degrades regulation performance
Solution Approach 1:
The patent replaces the analog ripple-based control system with a digital control system. The digital COT controller samples the inductor current using an ADC and processes the data digitally to generate PWM control signals, eliminating the analog ripple injection and comparison circuitry that caused output voltage offset errors while maintaining constant on-time control functionality
Solution Approach 2:
The patent introduces an intermediary digital processing stage between the current sensing and PWM generation. The ADC converts the analog inductor current to digital samples, which are then processed through digital arithmetic operations (adding reference current, comparing with threshold) before generating the PWM signal, thereby eliminating direct analog ripple injection that caused offset errors
2Measurement precision
If a digital COT controller with arithmetic devices is introduced, then output voltage offset can be cancelled and regulation performance enhanced, but device complexity increases
Solution Approach 1:
The digital COT controller integrates multiple functions into a single device: current sampling, ADC conversion, digital arithmetic operations (adding reference current, calculating ripple amplitude, comparing with threshold), and PWM generation. This multi-functional integration achieves offset cancellation while consolidating what would otherwise require multiple separate analog circuits
Solution Approach 2:
The patent changes the operating parameters and processing domain from analog continuous signals to digital sampled data. By operating in the digital domain with discrete samples and arithmetic operations, the system achieves precise offset cancellation through parameter manipulation (reference current addition, threshold comparison) without requiring complex analog circuitry
Data Source
AI summary
A digital constant on-time controller adaptable to a direct-current (DC)-to-DC converter includes a current sensing circuit that senses stored energy of the DC-to-DC converter, thereby generating a sense voltage; a semi-amplitude detector that detects half of a peak-to-peak amplitude of the sense voltage, thereby generating a semi-amplitude voltage; a DC voltage detector that detects a DC voltage across an effective series resistor of an energy storage circuit that provides the stored energy of the DC-to-DC converter, thereby generating a DC voltage; an arithmetic device that adds the sense voltage and the semi-amplitude voltage, from which the DC voltage and a predetermined reference signal are subtracted; and a pulse-width modulation (PWM) generator that generates a switch control signal according to a result of the arithmetic device.