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
1Measurement precision
If a common mode control loop is used to balance currents in sigma-delta modulators, then the nominal current values are made equal, but the circuit complexity increases and noise is not effectively cancelled
Solution Approach 1:
The patent extracts and eliminates the common mode control loop from the sigma-delta modulator circuit. By removing this separate control mechanism, the design achieves current balancing through the inherent operation of the quantized feedback path itself, thereby reducing circuit complexity while maintaining precision.
Solution Approach 2:
The patent merges the current balancing function into the main quantized feedback path. Instead of having a separate common mode control loop, the feedback mechanism simultaneously performs both quantization and current balancing functions, eliminating the need for additional control circuitry.
2Measurement precision
If a common mode control loop is used to balance currents, then nominal current equality is achieved, but noise cancellation is ineffective as noise remains as root-sum-square of individual components
Solution Approach 1:
The patent employs quantized feedback that directly balances the difference current between two paths. By feeding back the actual difference current rather than controlling common mode currents separately, the system achieves both current equality and effective noise cancellation through the feedback mechanism itself.
Solution Approach 2:
The patent uses asymmetric current paths where one path carries the input signal current and the other carries the feedback current. This asymmetric configuration allows the difference between the two paths to directly represent the quantization error, enabling effective noise cancellation while maintaining current balance.
3Ease of operation
If reference currents are used in the common mode control, then current balancing is possible, but the number of components increases and cost increases
Solution Approach 1:
The patent enables the circuit to self-balance currents through the quantized feedback mechanism without requiring external reference currents. The feedback path automatically adjusts to balance the difference current, making the circuit self-regulating and eliminating the need for additional reference current sources.
Solution Approach 2:
The patent makes the feedback current serve multiple functions: it provides quantized feedback for noise shaping and simultaneously acts as the balancing current for the two current paths. This multi-functionality eliminates the need for separate reference currents and control circuits.
4Manufacturing precision
If common mode control components are added to null the difference of two quantities, then nominal equality is achieved, but noise is not cancelled and circuit cost increases
Solution Approach 1:
The patent uses direct quantized feedback on the difference current between two quantities. By feeding back the actual difference rather than controlling the quantities separately through common mode control, the system achieves both precision equality and noise cancellation in a single integrated 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 design simplifies the circuit by reducing components and noise, as it eliminates the need for common mode control and reference currents, while maintaining effective quantized feedback and reducing noise to the level of the current sources.
Implementation Method 1
a capacitor connected between the drain of the first transistor and the drain of the second transistor
Implementation Method 2
a voltage to current converter comprising: first and second transistors, each transistor having a gate, a source and a drain; an input signal source connected between the gates of the first and second transistors
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.