Sigma-Delta Modulator Feedback Circuit Without Common-Mode Control
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Solution Overview
Problem
Sigma-delta modulators with common mode control loops are complex and costly, and they fail to effectively cancel noise in the difference of two quantities, as only the nominal value is made equal, leaving noise in the difference as the root-sum-square of individual noise components.
Innovation Solution
A sigma-delta modulator design without a common mode control loop, utilizing a voltage-to-current converter with transistors, capacitors, and switches to maintain an average charge on a capacitor at zero, eliminating the need for reference currents and reducing noise by directing all current to the feedback path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If common mode control loops are used in sigma-delta modulators, then current balance is maintained, but circuit complexity and cost increase
Solution Approach 1:
The patent removes the common mode control loop from the sigma-delta modulator circuit, extracting only the essential differential signal processing path. This eliminates the complexity and cost associated with common mode control while maintaining the core functionality of the modulator through direct feedback to the differential inputs.
Solution Approach 2:
Instead of using a common mode control loop to balance currents, the patent inverts the approach by directly feeding back the differential signal to the differential inputs without intermediate common mode control stages. This reversal of the conventional control path simplifies the circuit architecture.
2Measurement precision
If common mode control loops are used, then nominal current values are equalized, but noise cancellation is ineffective as noise remains as root-sum-square of individual components
Solution Approach 1:
The patent implements direct feedback of the quantized signal to the differential inputs of the transconductance amplifier. This feedback mechanism ensures that both nominal current equality and noise cancellation are achieved simultaneously, as the feedback directly compensates for differential errors including noise components without the interference of common mode control stages.
3Extent of automation
If quantization elements are used in the control loop, then analog to digital conversion is achieved, but noise is introduced that requires sophisticated high order control loops to suppress
Solution Approach 1:
The patent uses a simple feedback loop that directly connects the quantizer output to the differential inputs of the transconductance amplifier. This direct feedback path effectively suppresses quantization noise without requiring sophisticated high-order control loops, achieving noise shaping through the fundamental feedback mechanism inherent in the 1-bit sigma-delta modulator architecture.
Data Source
AI summary
Described herein is an improved apparatus for increasing the performance of a ΣΔ modulator, which may function as an ADC. In one embodiment, the ΣΔ modulator comprises a voltage to current converter, a capacitor connected between two outputs of the voltage to current converter to receive a differential input current, and a switch that can switch between connecting each output of the voltage to current converter to ground while disconnecting the other output of the voltage to current converter. In this embodiment, the ΣΔ modulator has no common mode control loop, and no reference current. This results in decreased complexity, i.e., fewer components, as well as reduced noise.