Feedback-Controlled Integrator Slew Boost for Fast ADC Settling
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Solution Overview
Problem
High-performance delta-sigma analog-to-digital converters (ΔΣ ADCs) face limitations in settling response due to the slew rate of operational transconductance amplifiers (OTAs), which is often restricted by power consumption, making it challenging to achieve fast settling without increasing bias current, especially in portable electronics.
Innovation Solution
A slew rate enhancement circuit dynamically applies a boost current to the integrator based on feedback signals, controlling the amount and polarity of the boost current to enhance the slew rate only when needed, thereby improving settling response with minimal additional power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If higher bias current is used for the OTA, then faster slew rate and settling response are achieved, but power consumption increases
Solution Approach 1:
The patent applies dynamic bias current adjustment by controlling the switching of PMOS transistors (304, 308) based on the feedback signal state. The bias current to the OTA is dynamically modified during operation - increasing when large signal transitions are detected and decreasing during normal operation - thereby achieving fast settling response only when needed while minimizing average power consumption
Solution Approach 2:
The patent changes the bias current parameter of the OTA based on operating conditions. By detecting the feedback signal state and controlling switch configurations, the bias current is adjusted between different levels to optimize the trade-off between settling speed and power consumption, achieving fast slew rate enhancement only when large signal transitions occur
2Speed
If dynamic boost current is applied to enhance slew rate, then fast settling response is achieved, but circuit complexity increases
Solution Approach 1:
The patent introduces control switches (PMOS transistors 304, 308) as intermediary elements that mediate between the feedback signal and the OTA bias current. These switches act as simple intermediaries that conditionally connect or disconnect bias current paths based on feedback signal states, adding minimal complexity while achieving dynamic slew rate enhancement
Solution Approach 2:
The patent uses the feedback signal directly to control the switching of bias current paths. The feedback signal state determines whether additional bias current is applied to the OTA, creating a simple feedback-based control mechanism that enhances slew rate dynamically without requiring complex control logic or additional sensing circuits
Data Source
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AI summary
Techniques for enhancing the slew rate of an active circuit within a feedback circuit (such as a ADC) are described. In one design, a ADC includes an integrator, a slew rate enhancement circuit, and a control circuit. The integrator receives an input signal and provides an output signal. The slew rate enhancement circuit enhances the slew rate of the integrator based on a feedback signal in the ADC. The slew rate enhancement circuit may provide (i) a boost current for only certain values (e.g., the largest and smallest values) of the feedback signal or (ii) different amounts of boost current for different values of the feedback signal. In one design, the slew rate enhancement circuit includes at least one boost circuit coupled to the integrator. Each boost circuit provides a boost current to enhance the slew rate of the integrator when that boost circuit is enabled.