Current-Input Delta-Sigma Modulator Node Balancing for Fast Settling
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Solution Overview
Problem
Current-input-type delta-sigma modulators experience instability when input changes sharply, leading to prolonged AD conversion times due to unbalanced states in the internal nodes.
Innovation Solution
Incorporating a short-circuit switch that short-circuits the first and second integration nodes, activated at timings when the nodes are out of balance, such as during sharp changes in the signal current or instability in the fixed current, to maintain a balanced state and reduce internal instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a current-input-type delta-sigma modulator is used, then AD conversion can be performed, but the internal state becomes unstable when input changes sharply, leading to prolonged settling time
Solution Approach 1:
The short-circuit switch is activated in advance when sharp input changes are detected, before the instability fully develops. By preemptively equalizing the potentials of the first and second integration nodes, the system prevents the buildup of unstable internal states, thereby maintaining both speed and stability during rapid transitions.
Solution Approach 2:
The short-circuit switch acts as an intermediary element between the first and second integration nodes. When activated, it provides a temporary direct connection that mediates the potential difference between nodes, allowing rapid equalization without requiring the complex feedback mechanisms to work through the entire conversion chain, thus stabilizing the internal state quickly.
2Loss of time
If the short-circuit switch is activated during sharp input changes, then internal state instability is reduced and settling time is shortened, but the circuit complexity increases
Solution Approach 1:
The stabilizing function is extracted as a separate, dedicated short-circuit switch mechanism rather than being integrated into the main feedback loop. This isolated component can be activated independently only when needed for sharp transitions, providing the stabilizing effect without permanently complicating the normal operation of the delta-sigma modulator circuit.
Solution Approach 2:
The short-circuit switch is designed with dynamic control, being activated only during specific conditions (sharp input changes) rather than remaining permanently engaged. This dynamic activation strategy allows the circuit to maintain simplicity during normal operation while providing enhanced stability performance only when required, optimizing the trade-off between complexity and performance.
Data Source
AI summary
Instability of an internal state in a current-input-type delta-sigma modulator is reduced in a case where input changes sharply.A signal current is input to a first integration node. A difference current between a fixed current and the signal current is input to a second integration node. A voltage-to-current converter that converts a difference voltage between the voltage of the first integration node and a first reference voltage into a current and outputs it is connected between the first integration node and the second integration node. The voltage of the second integration node is compared with a second reference voltage, and a 1-bit digital signal is output. Current is draws from the first integration node or the second integration node according to the 1-bit digital signal. A short-circuit switch is provided between the first integration node and the second integration node for short-circuiting them.