Switched Faraday Shield Sampling Circuit for Parasitic-Free Charge Transfer
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Solution Overview
Problem
Switched capacitor circuits face challenges in minimizing parasitic capacitance effects and maintaining dynamic range when interfacing differential signals to single-ended circuits, particularly due to the presence of parasitic capacitors and complex common-mode voltage control loops in differential input structures.
Innovation Solution
Incorporating a Faraday Shield that can be switched between nodes of the circuit, allowing for differential signal sampling and charge transfer without loss of dynamic range, by driving the shield with one side of the differential input pair during the charge sampling phase and disconnecting it to a dc bias voltage during the charge transfer phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential input structure is used to reject common-mode error signals, then common-mode rejection is improved, but the number of circuit components doubles and a complex common-mode feedback loop is required
Solution Approach 1:
The patent extracts the common-mode rejection function from the complex differential feedback loop and implements it through a simplified switched-capacitor circuit that samples the differential signal and transfers it to a single-ended integrator, eliminating the need for a continuous common-mode feedback loop while maintaining rejection of common-mode errors
Solution Approach 2:
The circuit segments the signal processing into distinct phases: a charge sampling phase where differential inputs are sampled onto capacitors, and a charge transfer phase where the sampled charge is transferred to the integrator. This segmentation allows common-mode rejection to be achieved through the differential sampling process itself rather than requiring a complex continuous feedback loop
2Object-affected harmful factors
If a Faraday Shield is connected to local ground to reduce parasitic capacitance effects, then parasitic capacitance rejection is improved, but ground voltage differences cause error signals when grounds are at different potentials
Solution Approach 1:
The Faraday shield is made dynamic by switching its connection between the local ground and the signal source ground according to the sampling phase. During the sampling phase, the shield connects to the signal source ground to minimize parasitic effects on the differential inputs. During the transfer phase, it connects to the local ground to maintain the integrator's reference. This dynamic switching eliminates ground voltage difference errors while maintaining parasitic capacitance rejection
Solution Approach 2:
The switched-capacitor circuit acts as an intermediary that transfers the differential signal charge to the single-ended integrator without requiring a continuous connection between different grounds. The Faraday shield, switched between grounds, mediates the parasitic capacitance management without introducing ground voltage difference errors into the signal path
3Loss of information
If the Faraday Shield is switched between nodes during charge sampling and transfer phases, then dynamic range is maintained without loss, but the switching mechanism adds circuit complexity
Solution Approach 1:
The Faraday shield serves multiple functions: it reduces parasitic capacitance effects on the differential inputs, it provides a reference potential for the sampling capacitors, and it maintains the dynamic range of the differential signal during transfer to the single-ended integrator. This multi-functionality justifies the switching mechanism while achieving multiple goals simultaneously
Solution Approach 2:
The Faraday shield is switched periodically between the signal source ground and the local ground, synchronized with the sampling and transfer phases of the switched-capacitor circuit. This periodic switching maintains the dynamic range during the critical sampling phase while providing proper reference during the transfer phase, achieving dynamic range preservation with a relatively simple periodic switching mechanism
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 solution effectively minimizes parasitic capacitance effects and maintains the dynamic range of the signal, enabling efficient interfacing of differential signals to single-ended circuits without introducing errors or signal loss.
Implementation Method 1
This invention relates to a sampling capacitor structure and clocking scheme for a switched capacitor circuit with a differential input signal. This differential input circuit has an electrostatic shield, also known as a Faraday Shield.
Data Source
AI summary
A sampling capacitor structure, which includes a Faraday Shield that can be switched between various nodes. In a switched capacitor circuit, this sampling capacitor structure allows for differential charging of the sampling capacitor while minimizing the effects of any parasitic stray capacitor. Furthermore, with appropriate switching of the Faraday Shield, once the differential charge sampling circuit samples the differential signal, this sampled differential charge can then be transferred to a downstream single-ended circuit, such as an integrator, without any loss of signal.