Sigma-Delta ADC with Embedded Low-Pass Filtering for SDR Dynamic Range
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Solution Overview
Problem
Conventional analog-to-digital converters (ADCs) in software-defined radio systems lack the dynamic range to effectively capture low-power radio signals, leading to distortion or blocking by spurious signals, and require additional components that increase power consumption and component count.
Innovation Solution
A filtering ADC circuit with a low-pass filter and a multi-feedback second-order sigma-delta modulator, incorporating a Class B DAC for feedback, which reduces noise and increases dynamic range by high-pass shaping analog and quantization noise, and using a capacitive feedback path to filter out-of-band interferers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ADCs are used in software-defined radio systems, then the system can perform digital signal processing, but the ADC lacks the dynamic range to capture low-power radio signals, leading to distortion or blocking by spurious signals
Solution Approach 1:
The patent combines a second-order low-pass filter with the sigma-delta ADC to form an integrated filtering ADC. This merging of filtering and conversion functions increases the effective dynamic range by attenuating spurious signals before they reach the quantizer, preventing distortion and blocking while maintaining the ability to capture low-power radio signals
Solution Approach 2:
The low-pass filter performs preliminary attenuation of out-of-band interferers and spurious signals before the signal enters the ADC conversion process. By pre-filtering the input signal, the system prepares the signal path to handle low-power signals without being overwhelmed by strong out-of-band interference, thereby extending the usable dynamic range
2Measurement precision
If additional components such as band-pass filters and low-noise amplifiers are added to improve signal capture, then the dynamic range and noise performance improve, but the power consumption and component count increase
Solution Approach 1:
The patent merges the low-pass filter functionality directly into the ADC structure, eliminating the need for separate baseband analog filtering components. This integration maintains noise performance by providing second-order filtering while reducing the component count and associated power consumption of discrete filter circuits
Solution Approach 2:
The filtering ADC serves multiple functions simultaneously: it performs analog-to-digital conversion while also providing second-order low-pass filtering to attenuate out-of-band interferers. This multi-functionality replaces what would traditionally require separate LNA, band-pass filter, and baseband filter components, reducing overall power consumption while maintaining noise performance
3Reliability
If additional components such as band-pass filters and low-noise amplifiers are added to prevent spurious signal interference, then the signal quality improves, but the device complexity and component count increase
Solution Approach 1:
The patent integrates a second-order low-pass filter directly into the sigma-delta ADC architecture, combining filtering and conversion functions in a single device. This integration maintains signal quality by effectively attenuating out-of-band interferers and spurious signals while reducing the component count compared to conventional approaches requiring separate filter and amplifier stages
Solution Approach 2:
The sigma-delta modulator inherently provides noise shaping that pushes quantization noise to higher frequencies, where the embedded low-pass filter can attenuate it. This self-service mechanism allows the ADC to improve its own signal quality and dynamic range without requiring external filtering components, thereby reducing device complexity while maintaining reliability
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 reduces the baseband analog section, improves noise performance, and decreases power consumption by embedding a second-order low-pass filter within the ADC, enhancing dynamic range and noise shaping while maintaining flexibility in digital processing.
Implementation Method 1
a current low pass filter connected to receive an incoming signal. The low pass filter may be connected to an integrator
Implementation Method 2
The low pass filter may be connected to an integrator
Implementation Method 3
A quantizer receives an output of the integrator to produce a digital signal as an output of the circuit
Implementation Method 4
A feedback path comprising a digital to analog converter (DAC) is connected between the output of the quantizer and an input of the integrator
Implementation Method 5
The integrator includes a capacitive feedback path between an output of the op-amp and its input
Data Source
AI summary
A filtering analog to digital converter (ADC) includes an integrator receiving at its input an analog input signal. A filtering capacitor at the input of the integrator filters out a large portion of out-of-band interferers in the analog input signal. The integrator produces an output that is quantized to produce a digital output. A feedback path between the quantizer output and the integrator input includes a digital to analog converter (DAC).