Switched-Capacitor Integrator Timing for ΔΣ Offset Charge Discharge
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Solution Overview
Problem
The accuracy of integration and modulation in ΔΣ modulation circuits is compromised due to operational amplifier offsets, leading to reduced modulation accuracy and increased distortion rates in ΔΣ modulation AD converters.
Innovation Solution
A switch control circuit that controls the on/off timing of switches in a complementary manner, ensuring that electric charge accumulated due to operational amplifier offsets is discharged before new integration occurs, thereby maintaining accurate integration and modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the integrator uses a switched capacitor and operational amplifier to perform sampling and integration processes, then the AD converter can achieve modulation function, but operational amplifier offsets cause charge accumulation that reduces integration accuracy and modulation precision
Solution Approach 1:
The patent applies preliminary action by discharging the accumulated charge from operational amplifier offsets before the integration process begins. The switch control circuit is designed to activate discharge switches (SW1, SW4) in advance to clear offset charges from capacitors (C12, C11), ensuring that the integration starts with a clean electrical state. This preliminary discharge action prevents offset accumulation from degrading integration accuracy and modulation precision during the actual signal processing.
2Measurement precision
If the on/off timing of switches is shifted to increase resolution, then the modulation accuracy improves, but the circuit complexity and timing control difficulty increase
Solution Approach 1:
The patent segments the switch control into distinct functional groups: sampling switches (SW2, SW3) that control charge accumulation during sampling, and discharge switches (SW1, SW4) that control offset charge removal. Each switch group is controlled by dedicated clock signals with specific timing relationships. This segmentation allows independent optimization of sampling and discharge operations, achieving high modulation accuracy through precise timing control while maintaining manageable circuit complexity through modular control architecture.
Solution Approach 2:
The patent implements periodic action through alternating sampling and discharge phases controlled by clock signals. The switch control circuit periodically switches between sampling mode (where SW2, SW3 are on and SW1, SW4 are off) and discharge mode (where SW1, SW4 are on and SW2, SW3 are off). This periodic alternation ensures that offset charges are systematically removed at regular intervals, maintaining integration accuracy over time while using simple repetitive timing patterns that are easy to generate and control.
3Measurement precision
If the sampling and integration processes are performed repeatedly to increase resolution, then the integration accuracy improves, but charge accumulation from operational amplifier offsets increases, degrading modulation accuracy
Solution Approach 1:
The patent converts the harmful effect of operational amplifier offset charges into a beneficial discharge mechanism. Instead of allowing offset charges to accumulate and degrade accuracy, the invention uses the same switched capacitor structure to actively remove these offset charges periodically. The discharge switches (SW1, SW4) are specifically designed to redirect offset charges to ground or reference potentials, transforming what would be a harmful accumulation into a controlled elimination process that actually improves long-term integration accuracy.
Solution Approach 2:
The patent implements feedback through the periodic discharge mechanism that monitors and corrects offset charge accumulation. The switch control circuit uses clock signals to periodically activate discharge switches, creating a feedback loop that continuously removes offset charges that would otherwise accumulate during repeated sampling and integration cycles. This feedback-based discharge approach ensures that integration accuracy is maintained over time by systematically eliminating the harmful charge accumulation effect.
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 approach enhances integration accuracy and modulation precision, reducing distortion rates in ΔΣ modulation AD converters by ensuring that charge from operational amplifier offsets is cleared before integration, thus improving overall performance.
Implementation Method 1
an integrator that integrates and outputs an input analog signal... an integration capacitor 111... the capacitor 111 accumulates the electric charge
Implementation Method 2
a switched capacitor and an operational amplifier... a capacitor 112... the capacitor 112 accumulates electric charge... the electric charge accumulated in the capacitor 112 flows into the integration capacitor 111
Data Source
AI summary
A switch control circuit turns on/off second and third switches, while turning off/on first and fourth switches, in a complementary manner in an integrator constituted by using a switched capacitor including the first to fourth switches and, where the first and fourth switches are turned off and the second and third switches are turned on, the switch control circuit turns on the second switch before turning off the fourth switch.