Capacitive DAC Switch Resistance Layout for Low-Distortion Output
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Solution Overview
Problem
Digital-analog converters experience distortion in analog output signals due to variations in the on-resistance value of switches, which affects the transient characteristics and distortion characteristics.
Innovation Solution
A digital-analog converter design that includes a sampling capacitive element, an operational amplifier, a summing node switch unit, and a feedback switch unit, where the on-resistance value of the MOS transistors in the summing node switch unit is set to be larger than that of the feedback switch unit, particularly during the initial period after connection, to minimize distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the on-resistance value of MOS transistors in the feedback switch unit is reduced to improve response speed, then the response speed of the analog output signal is improved, but the distortion characteristics deteriorate due to variations in on-resistance value
Solution Approach 1:
The patent changes the resistance parameter by making the summing node switch unit have a larger on-resistance value than the feedback switch unit. This parameter differentiation resolves the contradiction by allowing the feedback switch unit to maintain low on-resistance for fast response while the summing node switch unit has higher on-resistance to suppress distortion caused by on-resistance variations.
2Duration of action of moving object
If the on-resistance value of MOS transistors is made smaller to improve transient characteristics, then the transient response is improved, but the distortion of analog output signal increases
Solution Approach 1:
The patent applies local quality by assigning different on-resistance characteristics to different parts of the circuit: the feedback switch unit has small on-resistance for fast transient response, while the summing node switch unit has large on-resistance to minimize distortion. This localized differentiation of electrical properties resolves the contradiction between transient characteristics and distortion.
3Speed
If switches with low on-resistance are used to improve response speed, then the response speed is improved, but variations in on-resistance value cause distortion in analog output
Solution Approach 1:
The summing node switch unit acts as an intermediary between the digital input signals and the feedback path. By giving it a larger on-resistance value compared to the feedback switch unit, it mediates the signal flow in a way that reduces the impact of on-resistance variations, thereby maintaining signal accuracy while allowing the feedback path to provide fast response.
Data Source
AI summary
A digital-analog converter circuit includes sampling capacitive elements (111, 112, . . . , 11N) of which one ends are to be electrically connected to and disconnected from input terminals (D1, D2, . . . , DN), to which digital signals are input, via a switch unit (SWu10), an operational amplifier (501), a switch (301) capable of electrically connecting and disconnecting the other ends of the sampling capacitive elements (111, 112, . . . , 11N) and an inverting input terminal of the operational amplifier (501), and a switch unit (SWu40) that is disposed between nodes between the switch unit (SWu10) and the sampling capacitive elements (111, 112, . . . , 11N) and the output terminal of the operational amplifier (501) and capable of connecting and disconnecting them. An on-resistance value of a MOS transistor included in the switch (301) is set to be larger than an on-resistance value of a MOS transistor included in the switch unit (SWu40).