PWM DAC Switching Circuit for Wider Range and Better Linearity
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Solution Overview
Problem
Conventional PWM Digital-to-Analog Converter (DAC) circuits have limited range and non-linear output, which hampers their ability to generate precise voltage levels required for calibration devices.
Innovation Solution
The proposed PWM DAC circuit employs a configuration of operational amplifiers and switching networks, along with filter circuitry, to achieve a wider range of output voltage levels and improved linearity by dynamically controlling the coupling of signals and reference voltages based on input PWM signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional PWM DAC circuit is used, then the circuit structure is simple, but the output voltage range is limited and linearity is poor
Solution Approach 1:
The PWM DAC circuit is segmented into multiple independent operational amplifiers (first OP-AMP, second OP-AMP, third OP-AMP) that process different aspects of the signal conversion. Each OP-AMP handles specific functions: voltage level generation, signal inversion, and output buffering, allowing the system to achieve extended voltage range and improved linearity while maintaining modular simplicity
Solution Approach 2:
The circuit employs dynamic switching networks that change their electrical coupling states based on the PWM input signal. The switching networks dynamically connect or disconnect the OP-AMP outputs to reference voltages or to each other, enabling the circuit to adaptively adjust its transfer function and maintain linearity across an extended voltage range
2Manufacturing precision
If a conventional PWM DAC circuit is used, then the circuit is easy to manufacture, but the output linearity is poor
Solution Approach 1:
The third operational amplifier is configured with feedback from its output terminal to its second input terminal, creating a unity-gain buffer that improves output impedance and stabilizes the voltage output. This feedback mechanism ensures that the output voltage accurately follows the desired transfer function, improving linearity without significantly complicating the manufacturing process
Solution Approach 2:
The circuit changes its electrical parameters dynamically by switching between different coupling configurations. The switching networks alter the effective resistance and voltage division ratios based on the PWM duty cycle, enabling linear voltage output across an extended range while using standard, easily manufacturable components
3Adaptability or versatility
If the output voltage range is extended, then the linearity is improved, but the circuit complexity increases
Solution Approach 1:
The switching networks perform multiple functions simultaneously: they select reference voltages, control signal routing between OP-AMPs, and adjust voltage division ratios. This multi-functionality allows the circuit to achieve extended voltage range and improved linearity without requiring separate control mechanisms, thereby limiting the increase in overall complexity
Data Source
Figure 1
Figure 2A~2B
Figure 3A
AI summary
A pulse width modulation (PWM) digital-to-analog conversion circuit includes switches 102, 104, 114, 116 controlled by a first PWM signal, and switches 106, 108, 110, 112 controlled by a second PWM signal. A first operational amplifier (op-amp) 132 includes a first input coupled to an output of a filter, and a second input coupled to an output of the first op-amp. During a first time period, an output of a second op-amp 128 is coupled to an input of the filter via switches 102 and 104, and an output of a third op-amp 130 is coupled to the output of the first op-amp via switches 114, 116. During a second time period, the output of the second op-amp is coupled to the output of the first op-amp via switches 106, 108, and an output of the third op-amp is coupled to the input of the filter via switches 110, 112.