Delta-Sigma Modulator RC Integrator With Single-Op-Amp Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current delta-sigma modulators require a large number of operational amplifiers and capacitive elements to achieve high order integration characteristics, leading to increased power consumption and circuit area, making them less desirable for smaller and lower power applications.
Innovation Solution
A delta-sigma modulator configuration using a single operational amplifier with a high order RC low pass and high pass filter, along with a feedforward path and switch circuit to reduce the number of D-A converters and capacitive circuits, achieving third order integration characteristics with reduced size and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the order of continuous time filters is increased by cascading multiple integrators, then accuracy is improved, but the number of operational amplifiers increases causing increased power consumption and chip area
Solution Approach 1:
Multiple integrator functions are merged into a single operational amplifier by implementing a high order RC low pass filter and a high order RC high pass filter in the inverting input portion and negative feedback portion, respectively. This allows the single operational amplifier to achieve high order integration characteristics that traditionally required multiple cascaded integrators, thereby reducing power consumption while maintaining accuracy.
2Measurement precision
If the order of continuous time filters is increased by cascading multiple integrators, then accuracy is improved, but chip area increases
Solution Approach 1:
Multiple integrator functions are merged into a single operational amplifier by implementing a high order RC low pass filter and a high order RC high pass filter in the inverting input portion and negative feedback portion, respectively. This allows the single operational amplifier to achieve high order integration characteristics that traditionally required multiple cascaded integrators, thereby reducing chip area while maintaining accuracy.
3Measurement precision
If a high order RC low pass filter is provided in the inverting input portion to achieve high order integration characteristics, then integration performance is improved, but circuit area increases particularly because capacitive elements have large area
Solution Approach 1:
The high order RC low pass filter and high order RC high pass filter are combined within a single operational amplifier structure. The resistive and capacitive elements are shared between the two filter functions, reducing the total number of capacitive elements required compared to implementing separate filters, thereby reducing circuit area while achieving high order integration characteristics.
Solution Approach 2:
The RC elements in the inverting input portion and negative feedback portion serve dual purposes: they form both the high order RC low pass filter and the high order RC high pass filter simultaneously. This multi-functionality reduces the total number of passive components required, thereby reducing circuit area while achieving the desired high order integration characteristics.
4Measurement precision
If negative feedback is provided to intermediate nodes of high order RC filters, then high order integration characteristics are achieved, but the number of D-A converters increases and design becomes more difficult
Solution Approach 1:
Multiple negative feedback paths are merged into a single D-A converter by providing negative feedback to the inverting input end of the operational amplifier. The high order RC low pass filter and high order RC high pass filter work together to provide the required integration characteristics without requiring separate D-A converters for each feedback node, thereby reducing the number of D-A converters and simplifying design.
Data Source
AI summary
A delta-sigma modulator includes: an integrator having an operational amplifier; a quantizer quantizing an output of the integrator; a first D-A converter converting an output of the quantizer to a current signal to provide negative feedback to the operational amplifier; a feedforward path feeding forward an input of the integrator to the quantizer; and a second D-A converter converting the output of the quantizer to a current signal to provide negative feedback to the quantizer. The integrator includes a resistive element having a first end connected to the input of the integrator and a second end connected to an inverting input of the operational amplifier, n capacitive circuits connected in series between the inverting input and an output of the operational amplifier, and (n−1) resistive elements each having a first end connected to an interconnecting node of the capacitive circuits and a second end connected to a common node.