PWM DAC Switching Circuit for Linear Wide-Range Voltage Output
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Solution Overview
Problem
Conventional PWM DAC circuits have limited range and non-linear output, making them inadequate for generating precise voltage levels required in calibration devices.
Innovation Solution
A PWM DAC circuit design incorporating multiple operational amplifiers and switching networks, along with filter circuitry, to achieve a wider range of voltage outputs and improved linearity by dynamically controlling signal paths based on input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
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, second, and third OP-amps) with distinct functions. The first and second OP-amps process different input signals through separate switching networks, and their outputs are combined by the third OP-amp. This segmentation allows each amplifier to operate within optimized parameters, improving overall linearity and output range without requiring a single complex amplifier design.
Solution Approach 2:
The circuit employs dynamic switching networks that reconfigure signal paths based on input conditions. The switching networks dynamically connect or disconnect operational amplifiers and filter circuits, allowing the system to adapt its configuration for different output requirements. This dynamic reconfiguration enables the circuit to maintain linearity across a broader voltage range while managing complexity through controlled adaptability.
2Manufacturing precision
If switch resistance is present in the PWM DAC circuit, then the circuit is easier to manufacture, but the output precision deteriorates due to sensitivity to resistance variations
Solution Approach 1:
The third operational amplifier is configured with feedback from its output to its inverting input, creating a closed-loop system. This feedback mechanism continuously monitors the output voltage and adjusts the amplifier's operation to compensate for voltage drops caused by switch resistance. The feedback loop effectively cancels out the impact of resistance variations, maintaining output precision without requiring ultra-low resistance switches.
Solution Approach 2:
The operational amplifiers act as intermediary elements between the switching networks and the final output. These high-precision amplifiers buffer and condition the signals, isolating the output from the effects of switch resistance. The amplifiers' high input impedance and low output impedance characteristics minimize the impact of resistance variations in the switching networks, allowing the use of standard switches rather than specialized low-resistance components.
3Adaptability or versatility
If the output voltage range is expanded beyond conventional limits, then the versatility of the calibration device is improved, but the linearity of the output deteriorates
Solution Approach 1:
The voltage range expansion is achieved through segmentation of the output generation across multiple operational amplifiers. The first and second OP-amps generate intermediate voltage levels through duty-cycle modulation, and the third OP-amp combines these outputs to achieve the final expanded voltage range. Each amplifier operates within a limited, linear range, but their combined output spans a broader voltage range while maintaining linearity through the superposition principle.
Data Source
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) 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 is coupled to an input of the filter via switches 102 and 104, and an output of a third op-amp is coupled to the output of the first op-amp via switches 114 and 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 and 108, and an output of the third op-amp is coupled to the input of the filter via switches 110 and 112.