Switched Capacitor Inverter Circuit With Virtual Ground Offset
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Solution Overview
Problem
Switched capacitor circuits, particularly those using operational-transconductance amplifiers (OTA), consume high power and occupy large circuit areas, limiting their efficiency and integration in CMOS processes.
Innovation Solution
A switched capacitor circuit design utilizing a single-ended inverter and an offset unit to create a virtual ground node, reducing power consumption and integrated circuit area by using an inverter instead of an OTA, with a charging unit, an integrating unit, and an offset unit connected through capacitors and switches controlled by non-overlapping clock signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an operational-transconductance amplifier (OTA) is used in a switched capacitor circuit, then accurate charge transfer and signal processing are achieved, but power consumption increases and circuit area expands
Solution Approach 1:
The patent extracts the essential function of the OTA (charge transfer and signal processing) and implements it using simpler components: an inverter, sampling capacitor, and switching elements. This removes the power-consuming OTA while maintaining the core functionality through capacitive charge transfer mechanisms controlled by non-overlapping clock signals.
Solution Approach 2:
The patent creates a functional copy of the OTA's charge transfer capability using a different physical approach - instead of using the transconductance property of an active amplifier, it uses passive capacitive coupling with controlled switching. The inverter copies the signal processing function while consuming significantly less power.
2Measurement precision
If an operational-transconductance amplifier (OTA) is used in a switched capacitor circuit, then accurate charge transfer and signal processing are achieved, but circuit area increases
Solution Approach 1:
The patent removes the large-area OTA component and replaces it with compact elements: a small inverter, minimal capacitors, and switches. This extraction of the essential function from its bulky implementation dramatically reduces the circuit footprint while maintaining integration compatibility with CMOS processes.
Solution Approach 2:
The patent creates a compact functional equivalent of the OTA using planar capacitor and switch structures that occupy minimal silicon area. The inverter-based implementation copies the signal processing function in a space-efficient manner suitable for high-density integrated circuit fabrication.
3Use of energy by moving object
If a single-ended inverter is used instead of an OTA, then power consumption and circuit area are reduced, but maintaining virtual ground and accurate charge transfer becomes more difficult
Solution Approach 1:
The patent introduces an offset unit as an intermediary component that mediates between the simple inverter and the charge transfer function. This offset unit, implemented with capacitors and switches, creates the virtual ground condition at the inverter input without requiring a complex amplifier, thus maintaining functionality while preserving the low-power advantage.
Solution Approach 2:
The patent prepares the circuit state in advance by using the offset unit to establish the virtual ground condition before the main charge transfer operation. The sampling and integration phases are pre-configured through clock-controlled switching, ensuring that the inverter operates in the optimal region for accurate charge transfer without requiring complex real-time control.
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
The solution achieves reduced power consumption and smaller integrated circuit area while maintaining accurate charge transfer and signal processing, with the inverter-based circuit effectively addressing the limitations of OTA-based designs.
Implementation Method 1
the sampling capacitor accumulates charge corresponding to an input signal during a sampling mode
Implementation Method 2
the feedback capacitor receives charge from the sampling capacitor during the integrating mode
Data Source
AI summary
A switched capacitor circuit includes an amplifier, a charging unit, an offset unit, and an integrating unit. The charging unit is coupled between an input node and a first node, and is for accumulating charge corresponding to an input signal during a sampling mode. The offset unit is coupled between the first node and an input of the amplifier, and is for maintaining the first node to be a virtual ground during an integrating mode. The integrating unit is coupled between the first node and an output of the amplifier, and is for receiving charge from the charging unit during the integrating mode.