Frequency-Selective Down-Conversion Circuit With 1/f-Noise Feedback Control
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Solution Overview
Problem
Existing frequency translating delta sigma modulators for radio receivers are limited by low-Q resonators, leading to inadequate frequency selectivity and increased stopband attenuation requirements, as well as nonidealities in feedback D/A-conversion and frequency up-conversion, which degrade performance and introduce 1/f-noise.
Innovation Solution
A frequency selective circuit with impedance transferring circuits, comprising a transconductance amplifier and a switching arrangement, is used to switch impedance from base band to the frequency of the input signal, enabling band pass filtering and down mixing, and incorporating a feedback loop to control the properties of the circuit, thereby improving noise performance and reducing sensitivity to 1/f-noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If low-Q resonators are used in the first stage of band pass modulators, then device complexity is reduced, but frequency selectivity deteriorates and stopband attenuation requirements increase
Solution Approach 1:
The patent changes the Q-parameter of resonators from low-Q to high-Q throughout the signal path, including in the feedback path. This parameter change improves frequency selectivity and reduces stopband attenuation requirements while maintaining reasonable device complexity through systematic design of high-Q resonator stages.
2Device complexity
If unfiltered 1-bit bitstream feedback signal is used, then device complexity is reduced, but performance deteriorates due to high spectral energy mixing and nonidealities in feedback D/A-conversion and frequency up-conversion
Solution Approach 1:
The patent applies preliminary filtering to the feedback bitstream signal before it enters the feedback D/A-converter and frequency up-conversion stage. This preliminary action removes high spectral energy components that would otherwise mix with the desired signal band, preventing performance degradation from the outset.
Solution Approach 2:
The patent introduces feedback filtering in the feedback path to control and improve modulator performance. The filtered feedback signal reduces the impact of nonidealities in feedback D/A-conversion and frequency up-conversion, thereby improving overall system reliability and performance.
3Adaptability or versatility
If frequency translating delta sigma modulators are used, then analog base band filtering and A/D-conversion bandwidth adjustments are simplified, but noise performance deteriorates due to 1/f-noise and nonidealities in feedback conversion
Solution Approach 1:
The patent implements feedback filtering to suppress 1/f-noise and reduce the impact of nonidealities in feedback D/A-conversion and frequency up-conversion. The feedback loop with proper filtering shapes the noise spectrum, pushing 1/f-noise away from the signal band and improving overall noise performance.
Solution Approach 2:
The patent optimizes various parameters including resonator Q-values, feedback filtering characteristics, and sampling frequencies to improve noise performance. By carefully selecting and adjusting these parameters, the system achieves better noise performance while maintaining adaptability to different receiver standards.
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
This solution allows for better noise performance and reduced sensitivity to 1/f-noise, enabling greater amplification at earlier stages and eliminating the need for coefficient or time constant modifications across most radio standards, as the final channel selection filter is realized in the digital domain.
Implementation Method 1
a switching arrangement and an impedance circuit connected in series, the switching arrangement being configured to switch the impedance of the impedance circuit from base band to the frequency of the input signal
Implementation Method 2
a transconductance amplifier, and a switching arrangement and an impedance circuit connected in series
Implementation Method 3
a frequency selective circuit with one or more resonator stages
Data Source
AI summary
Various embodiments are disclosed relating to techniques of filtering and down-converting a received signal. In accordance with an example embodiment of the present invention, an analog signal may be received and amplified in a transconductance amplifier. The amplified signal may be connected to a switching arrangement and an impedance circuit connected in series, and frequency down-converted in a second circuit. The resulting analog base band signal may be fed back to a base band input between the switching arrangement and the impedance circuit.