Current-Steering DAC Feedback Circuit for Higher Output Resistance
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Solution Overview
Problem
Current-steering digital-to-analog converters face challenges in minimizing differential nonlinearity (DNL) and maximizing spurious-free dynamic range (SFDR), which are influenced by the output resistance Runit, requiring an increase in output resistance to achieve better performance.
Innovation Solution
The implementation of a current-steering DAC with a bit current-steering circuit comprising a current source circuit, a first switch, a first feedback circuit, and a first amplifier circuit, where the feedback circuit and amplifier circuit are coupled to the switch to enhance the output resistance, and a large resistance value in the feedback circuit is designed to prevent electro-static discharge (ESD) and mitigate clock feedthrough effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output resistance Runit is increased to minimize DNL and maximize SFDR, then the DAC performance is improved, but the device complexity increases due to the need for additional feedback circuits and amplifier circuits
Solution Approach 1:
The patent applies feedback principle by introducing a feedback circuit that includes a transistor and resistance element connected to the switch. The feedback circuit senses the switch state and provides feedback signal to control the switch, thereby increasing the output resistance Runit without requiring complex external circuitry. This resolves the contradiction by achieving improved DNL and SFDR performance through internal feedback mechanisms.
Solution Approach 2:
The patent uses an intermediary approach by introducing a feedback transistor and resistance element as intermediary components between the switch and the output. These intermediary elements modify the switch behavior and increase the effective output resistance, allowing performance improvement without directly complicating the main DAC structure.
2Reliability
If a large resistance value is used in the feedback circuit to prevent ESD and mitigate clock feedthrough effects, then the reliability is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by selecting specific resistance values for the feedback circuit components. By carefully choosing the resistance value to be sufficiently large, the circuit achieves ESD protection and clock feedthrough mitigation. The large resistance value limits current flow during ESD events and reduces the impact of clock feedthrough, thereby improving reliability without requiring extremely precise manufacturing tolerances.
Data Source
AI summary
A DAC has at least one bit current-steering circuit. In the DAC, the current-steering circuit has a current source circuit, a switch, a feedback circuit, and an amplifier circuit. The current source circuit is disposed for outputting a bias current to the switch and coupled to the amplifier circuit. The switch has a first input/output terminal coupled to output an analog signal, a control terminal coupled to the feedback circuit, and a second input/output terminal for receiving the bias current, so that the first switch determines whether the first and the second input/output terminals are conducted according to a status of the control terminal.