Shared Reference Delta-Sigma Converters With Voltage Droop Compensation
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Solution Overview
Problem
Switched-capacitor delta-sigma data converters experience gain errors due to voltage droop caused by leakage in reference capacitors when other converters sharing the same voltage reference are disabled, leading to inaccuracies in integrated circuits like CODECs and SoCs.
Innovation Solution
A voltage droop compensation circuit is introduced to address this issue by compensating for current leakage through switches in the reference feedback switched-capacitor networks, using selectable resistances, switch states, or feedback mechanisms to maintain filter capacitor voltage and correct gain errors in active converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple data converters share the same voltage reference to conserve die area and power, then area and power consumption are reduced, but gain error occurs due to voltage droop from leakage in disabled converters
Solution Approach 1:
The patent segments the reference capacitor network into multiple independent reference capacitors, each associated with a specific data converter. This allows the reference voltage to be maintained separately for each converter, preventing leakage from disabled converters from affecting the reference voltage seen by active converters, thus resolving the gain accuracy issue while maintaining area efficiency through shared reference generation circuitry.
Solution Approach 2:
The patent introduces a reference capacitor as an intermediary element between the voltage reference and the data converters. This reference capacitor acts as a buffer that isolates the reference voltage from leakage effects, maintaining stable reference voltage levels even when converters are disabled, thereby preserving measurement precision while enabling shared reference architecture.
2Use of energy by moving object
If a data converter is placed in power-down mode to save power, then power consumption is reduced, but voltage droop occurs across the reference filter capacitor due to leakage
Solution Approach 1:
The patent applies preliminary action by pre-charging the reference capacitor to the reference voltage level before the data converter enters power-down mode. This ensures that the reference capacitor maintains the correct voltage level throughout the power-down period, compensating for leakage effects and preventing voltage droop that would otherwise occur during the disabled state.
Solution Approach 2:
The patent maintains continuity of useful action by keeping the reference capacitor charged and connected to the reference voltage through periodic refreshing or continuous connection during the power-down mode. This ensures that the reference voltage remains stable and continuous even when the data converter is disabled, preventing voltage droop and maintaining reference integrity.
3Use of energy by moving object
If the switching network is disabled in power-down mode, then power consumption is reduced, but leakage through transistors causes significant voltage droop
Solution Approach 1:
The patent extracts the reference capacitor from the switched-capacitor network and makes it independent of the switching network's power-down state. This allows the reference capacitor to remain charged and functional even when the switching network is disabled, isolating the reference voltage maintenance function from the power-consuming switching operations and eliminating leakage-induced voltage droop.
Solution Approach 2:
The reference capacitor serves itself by maintaining the reference voltage through its inherent charge storage capability, without requiring continuous switching operation. Once charged to the reference voltage, it can maintain this voltage level autonomously during power-down modes, providing self-service reference voltage stability independent of the switching network's operational state.
Data Source
AI summary
An integrated circuit having multiple switched-capacitor delta-sigma data converter circuits includes compensation for voltage reference error due to leakage current that causes reference voltage droop. The reference filter capacitor terminal voltage is maintained by periodic connection to the reference feedback capacitor(s) that are alternately connected to a voltage reference buffer, and the leakage into the reference feedback capacitor networks of disabled converter circuits causes reference voltage droop. The compensation is either determined from the number of converter circuits that are disabled, or from an error between the filter capacitor voltage and a separate voltage reference, and may be applied by adjusting a resistance selectively coupled between the voltage reference buffer output and the filter capacitor, feedback applied to the voltage reference buffer or its input source. Alternatively, or in combination, correction may be applied to the output of the active converters by digital adjustment of output values.