Continuous-Time Delta-Sigma Modulator With Stable SC Feedback Charge
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Solution Overview
Problem
Continuous-time delta-sigma modulators face instability due to variations in production processes and operating temperatures, leading to fluctuations in feedback charge amounts, which increase noise levels and affect stability.
Innovation Solution
A delta-sigma modulator with a switched-capacitor feedback DAC converter, featuring a variable reference voltage controlled by a reference-voltage generating circuit, ensures a constant feedback charge amount by using a replica circuit, detecting circuits, and amplifiers to stabilize the feedback loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switched-capacitor feedback DAC is used to improve jitter tolerance, then the tolerance to timing jitter is improved, but the feedback charge amount becomes sensitive to production process variations and temperature changes
Solution Approach 1:
The patent implements a feedback mechanism where the actual feedback charge amount is measured and compared with a target value, and the reference voltage is adjusted based on the difference. This closed-loop control compensates for variations caused by production process deviations and temperature changes, maintaining stable feedback charge amount while preserving the jitter tolerance benefits of the switched-capacitor structure.
Solution Approach 2:
The patent dynamically adjusts the reference voltage parameter to compensate for variations in feedback charge amount. By changing the reference voltage based on detected deviations, the system maintains a constant feedback charge amount despite changes in capacitance values due to production variations or temperature effects.
2Device complexity
If fixed reference voltage is used in switched-capacitor feedback DAC, then circuit simplicity is maintained, but feedback charge amount varies with production process and temperature
Solution Approach 1:
The patent introduces a feedback control system that measures the actual feedback charge amount and adjusts the reference voltage accordingly. This adds complexity to the circuit but ensures consistent feedback charge amount across different production processes and temperature conditions by continuously compensating for variations.
3Speed
If analog feedback is used in continuous-time delta-sigma modulator, then continuous signal processing is achieved, but jitter noise is added to the input signal
Solution Approach 1:
The patent replaces the traditional analog feedback path with a switched-capacitor feedback DAC that operates in a hybrid manner. The digital quantizer output controls switches to transfer charge packets, effectively substituting continuous analog voltage feedback with a pulsed charge transfer mechanism that is less sensitive to timing jitter while maintaining continuous-time operation at the analog interface.
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 maintains a stable feedback amount, reducing noise and ensuring operational stability despite variations in production processes and temperatures, thereby enhancing the modulator's performance.
Implementation Method 1
A switched-capacitor feedback DA converter which outputs an analog signal depending on a first reference voltage according to a digital signal output from the quantizer and feeds back the analog signal to the continuous-time loop filter
Implementation Method 2
the switched-capacitor feedback DA converter having a capacitor and a resistor; wherein the switched-capacitor feedback DA converter attenuating the output signal to be fed back to the continuous-time loop filter according to a time constant determined by the capacitor and the resistor
Data Source
AI summary
The present invention provides a continuous-time delta-sigma modulator which is configured with an SC (SCR) feedback DA (103) for improving tolerance to jitter for a clock signal and operates stably by maintaining a certain feedback amount without being influenced by a change in a production process thereof or an operating temperature condition thereof. By adjusting a reference voltage Vref that determines an output voltage of the SC feedback DA (103), it is possible to feed back a certain amount of charge from the SC feedback DA (103) to a loop filter (101). Thereby, operation of the delta-sigma modulator is stabilized.