Capacitor-Based DAC Using Pass Resistor for Low Voltage CMOS
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Solution Overview
Problem
Conventional direct-charge transfer (DCT) digital-to-analog converters (DACs) face challenges in operating at low supply voltages due to the limitations of MOS switches, which struggle to conduct signals effectively when the supply voltage is near half the voltage level, making it difficult to implement DCT DACs using CMOS fabrication technology.
Innovation Solution
The implementation of a DCT DAC that replaces the MOS switch S4 with a pass resistor, allowing the DAC to operate in low voltage environments and be compatible with CMOS process technology, where the pass resistor is connected between the output terminal of the operational amplifier and the input capacitor, enabling charge sharing and current output generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If MOS switches are used in DCT DAC implementation, then the DAC can be integrated with CMOS fabrication technology, but the DAC cannot operate effectively at low supply voltages near half the voltage level
Solution Approach 1:
The patent changes the operating parameters of the switch by replacing the MOS switch with a pass resistor, which has different voltage-dependent characteristics. The pass resistor maintains consistent resistance across the voltage range, unlike MOS switches whose resistance varies significantly at low voltages, thereby enabling reliable low-voltage operation while maintaining CMOS compatibility
Solution Approach 2:
The pass resistor acts as an intermediary element between the capacitors in the DCT DAC circuit. It mediates the charge transfer process by providing a controlled resistance path that enables proper charge sharing and signal transmission at low supply voltages, overcoming the limitations of direct MOS switch connection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables the DCT DAC to function effectively at low supply voltages by stabilizing charge redistribution and maintaining operational efficiency, ensuring the DAC can be integrated into chip circuits without the limitations imposed by MOS switch forbidden ranges, thus overcoming the issues of low voltage compatibility.
Implementation Method 1
The input capacitor stores a charge sample according to a digital input signal and a previous output analog signal
Implementation Method 2
The analog output circuit has a feedback capacitor to share the charge sample and accordingly generates a current output analog signal from an output node
Data Source
AI summary
A digital-to-analog converter (DAC) compatible with CMOS technology and operable in low voltage applications. An input capacitor stores a charge sample according to a digital input signal and a previous output analog signal. An analog output circuit has a feedback capacitor to share the charge sample and accordingly generate a current output analog signal from an output node. The output node may be continually connected to the input capacitor through a pass resistor.