Comparator-Based Switched-Capacitor Circuit With Constant Total Current
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Solution Overview
Problem
Conventional comparator-based switched-capacitor circuits suffer from decreased linearity due to the dependency of the output current on the output voltage, affecting the performance of circuits like multiplying DACs and pipelined ADCs.
Innovation Solution
The proposed solution involves a comparator-based switched-capacitor circuit with a dual current source configuration, utilizing NMOS and PMOS transistors and buffer circuits to maintain a constant total current, thereby reducing the impact of output voltage variations on linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional current source (MOSFET) is used in the comparator-based SC circuit, then the circuit structure is simple, but the output current is dependent on the output voltage which decreases the linearity of the circuit
Solution Approach 1:
The current source is divided into two separate current sources (first current source and second current source) that operate in opposite polarities. Each current source is independently controlled by the comparator output, allowing them to compensate for each other's voltage dependencies and achieve higher linearity.
Solution Approach 2:
The first and second current sources are combined in parallel to form a composite current source. Their outputs are summed at the summing node, creating a total current that remains constant despite voltage variations, as the NMOS and PMOS transistors compensate for each other's non-linearities.
2Reliability
If a single current source is used to control the output voltage, then the control is simple, but the output current varies with output voltage affecting circuit performance
Solution Approach 1:
The comparator continuously monitors the voltage at the summing node and adjusts the control signals to the first and second current sources accordingly. This feedback mechanism ensures that the total current remains constant by compensating for any deviations caused by voltage variations, thereby improving circuit reliability.
Solution Approach 2:
The invention changes the operating parameters of the current sources by using dual-polarity control signals from the comparator. The first current source operates with one polarity while the second operates with the opposite polarity, allowing the total current to remain constant despite changes in output voltage, thus improving circuit performance.
Data Source
AI summary
A comparator-based switched-capacitor circuit has a first output terminal and a second output terminal, and includes a switch-capacitor network, a first current source, and a second current source. Each of the first current source and the second current source includes a first transistor, a second transistor, a capacitor, and a buffer circuit. The first transistor has a first source, a first drain, and a first gate. The first drain is coupled to the first output terminal, the first source is coupled to a reference voltage, and the first gate is coupled to the switch-capacitor network. The second transistor has a second source, a second drain, and a second gate. The second source is coupled to the first output terminal. The capacitor is coupled between the second gate and the second source. The buffer circuit is coupled between the second source and the second drain.