PWM Output Pulse Timing for Thermal Noise Reduction
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Solution Overview
Problem
Conventional pulse-width modulation (PWM) techniques suffer from increased noise contribution due to thermal fluctuations in power supplies, especially in low-power electronic devices where signal-to-noise ratio (SNR) requirements are stringent.
Innovation Solution
The solution involves adjusting the time duration that switches drive the output node, reducing noise by operating switches for shorter durations when a small signal is desired and longer durations when a larger signal is needed, with a duty cycle below fifty percent, and dynamically adjusting based on the envelope level of the reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If switches operate continuously in conventional PWM, then output signal is generated, but thermal noise increases
Solution Approach 1:
The patent applies periodic action by implementing a noise reduction technique where both switches are coupled to the output node for specific time durations within each PWM cycle. This periodic simultaneous coupling creates intervals where noise from both power supplies is present, allowing the system to reduce overall thermal noise while maintaining signal output functionality.
2Use of energy by moving object
If power supply voltage is reduced to decrease power consumption, then energy efficiency improves, but noise contribution increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the time duration that both switches are coupled to the output node based on the envelope level of the reference signal. When the envelope level indicates a small desired output signal, the simultaneous coupling duration is reduced, which reduces thermal noise. This allows the system to maintain low power consumption while adaptively controlling noise levels according to signal requirements.
3Object-generated harmful factors
If switch operating duration is reduced to reduce noise, then thermal noise decreases, but signal level may be insufficient
Solution Approach 1:
The patent applies dynamics by making the switch operating duration adaptive rather than fixed. The control circuit dynamically adjusts the time duration that both switches are coupled to the output node based on real-time envelope level detection of the reference signal. This dynamic adjustment ensures that when larger signal levels are needed, the switches operate longer to provide sufficient signal power, while when smaller signals are needed, the operating duration is reduced to minimize thermal noise.
Data Source
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Figure 2A
Figure 2B~3A
AI summary
Noise introduced in an output signal of a pulse-width modulator (PWM) may be reduced by changing the time duration that a switch is driving the output node. Because the power supplies coupled to the switches are the source of noise in the output signal of the PWM, the time duration that the power supplies are driving the output may be reduced to obtain a subsequent reduction in noise in the output signal. For example, when a small signal is desired to be output by the PWM, the switches may be operated for shorter time durations. Thus, the switches couple the noise sources to ground for a duration of a cycle to reduce contribution of noise to the output. But, when a larger signal is desired to be output by the PWM, the switches may be operated for longer time durations or the conventional time durations described above.