System and method for bandpass sigma-delta modulation
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Solution Overview
Problem
Existing bandpass sigma-delta modulators face challenges in achieving high-speed operation and satisfactory performance, especially in CMOS/BiCMOS technology, due to limitations in discrete-time and continuous-time implementations, and require costly III-V processes with high power consumption.
Innovation Solution
A continuous-time bandpass sigma-delta modulator employing an electromechanical filter with a multi-feedback structure and a wideband transimpedance amplifier, mimicking the transfer function of a discrete-time modulator prototype, using MEMS, BAW, or SAW filters to achieve stable and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If discrete-time bandpass sigma-delta modulators using switched-capacitor circuits are used, then the circuit implementation is straightforward, but the operating speed is limited and cannot operate at high speed
Solution Approach 1:
The patent replaces the electronic switched-capacitor mechanism with an electromechanical resonator system. The electromechanical filter uses mechanical resonance at a specific frequency to achieve bandpass filtering, substituting the need for high-speed electronic switching with a mechanically resonant system that naturally operates at the desired frequency, thereby enabling high-speed operation without complex switching circuits
Solution Approach 2:
The patent changes the fundamental operating parameter from electronic switching frequency to mechanical resonance frequency. By designing the electromechanical resonator to resonate at the target bandpass frequency, the system achieves high-speed operation inherent to the mechanical resonance rather than being limited by electronic switching speeds and capacitor charging/discharging times
2Reliability
If continuous-time bandpass sigma-delta modulators based on active-RC, Gm-C or LC filters are used, then high-speed operation is achieved, but performance is degraded due to process and temperature variation in CMOS/BiCMOS processes
Solution Approach 1:
The patent replaces temperature-sensitive electronic filters (active-RC, Gm-C, LC) with an electromechanical resonator whose resonance frequency is determined by physical dimensions and material properties rather than electrical components. This mechanical resonance frequency remains stable across temperature variations and process changes, providing reliable performance without the PTV issues that plague CMOS/BiCMOS implementations of electronic filters
Solution Approach 2:
The electromechanical resonator acts as an intermediary between the input signal and the sigma-delta modulation process. Instead of using electronic filters that are directly affected by process and temperature variations, the mechanical resonator provides a stable frequency-selective element that mediates the signal processing, isolating the system from environmental variations
3Adaptability or versatility
If multiple electromechanical resonators with different center frequencies are used to achieve wider passband, then the passband width increases, but the system becomes difficult to realize due to increased parasitics and complexity
Solution Approach 1:
The patent segments the filtering function into multiple cascaded electromechanical resonators, each handling a specific frequency band. By dividing the overall passband requirement into smaller segments that can be achieved by individual resonators, the system achieves a wider effective passband while keeping each individual resonator simple and manageable, avoiding the complexity of trying to achieve the full passband with a single complex resonator
Solution Approach 2:
The patent combines multiple electromechanical resonators in a cascaded configuration where each resonator contributes to the overall passband. By merging the frequency responses of multiple simpler resonators, the system achieves a wider composite passband with reduced individual parasitics compared to a single high-order resonator, thereby reducing overall system complexity
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 enables accurate center frequency control without frequency tuning and low power consumption, achieving stable and high-performance bandpass sigma-delta modulation with improved signal-to-noise plus distortion ratio and reduced power usage.
Implementation Method 1
BP ΣΔMs based on electromechanical resonators have been proposed recently
Implementation Method 2
A 47.3-MHz SAW Resonator Based CMOS Second-Order Bandpass Sigma-Delta Modulator
Implementation Method 3
a feedback circuit coupled between an output from the quantizer and an input of the electromechanical filter
Implementation Method 4
a quantizer coupled to an output from the electromechanical filter
Data Source
AI summary
Various embodiments of this disclosure may describe a bandpass sigma-delta modulator (BP ΣΔM) comprising an electromechanical filter, a quantizer coupled to the electromechanical filter, and a feedback circuit coupled between the quantizer and the electromechanical filter. Other embodiments be also be disclosed or claimed.