Dual-DAC Circuit Selection for Out-of-Band Noise Suppression
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Solution Overview
Problem
Conventional digital-to-analog converters (DACs) fail to effectively suppress conversion noise at out-of-band frequencies, with Nyquist-rate DACs having low noise reduction capabilities and noise shaping DACs requiring oversampling, which increases power consumption and limits noise reduction across all frequencies.
Innovation Solution
A digital-to-analog conversion circuit that selects between multiple DACs based on the frequency distance between the digital signal and the out-of-band frequency, using a control circuit to choose between Nyquist-rate and noise shaping DACs, optimizing noise suppression while considering power consumption and noise tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If noise shaping DAC is used to decrease noise level at out-of-band frequency, then noise suppression is improved, but power consumption increases due to oversampling requirement
Solution Approach 1:
The patent implements dynamic selection between Nyquist-rate DAC and noise shaping DAC based on the duplex distance parameter. The control circuit determines which DAC architecture to use by evaluating the frequency distance between transmit and receive bands, allowing the system to adaptively optimize the balance between noise suppression performance and power consumption requirements for different communication standards
Solution Approach 2:
The patent changes the operational parameter (duplex distance) to determine the optimal DAC configuration. By evaluating whether the duplex distance is less than or greater than a threshold value, the system selects between two different noise characteristics (white noise for Nyquist-rate DAC vs. shaped noise for noise shaping DAC), thereby optimizing performance across varying frequency separation conditions
2Object-affected harmful factors
If noise shaping DAC is used to suppress conversion noise, then noise level at specific out-of-band frequency is reduced, but the frequency range for effective noise reduction is limited
Solution Approach 1:
The patent segments the frequency domain into two distinct regions based on duplex distance: a first frequency region where noise shaping DAC is optimal (duplex distance less than threshold) and a second frequency region where Nyquist-rate DAC is optimal (duplex distance greater than threshold). This segmentation allows each DAC type to operate in its optimal frequency range, maximizing overall adaptability across different communication standards
3Object-affected harmful factors
If DAC resolution is increased to lower noise level, then noise suppression is improved, but analog design complexity and chip area increase
Solution Approach 1:
The patent employs a Nyquist-rate DAC with relatively low resolution (e.g., 6 bits) that produces white noise characteristics, which is sufficient when the duplex distance is large. This approach avoids the complexity and large chip area of high-resolution DACs by relying on frequency separation to naturally attenuate out-of-band noise, making the solution economically and physically efficient for wideband applications
Data Source
AI summary
A digital-to-analog conversion circuit includes a first digital-to-analog converter (DAC), a second DAC, and a control circuit to select which DAC to use for digital-to-analog conversion of a digital signal. Concerned with the noise level produced at a given out-of-band frequency, the control circuit bases its selection of DACs, at least in part, on a frequency distance between the given out-of-band frequency and the digital signal's frequency. The control circuit, for example, may select the DAC producing the lowest noise level at that frequency distance, or, if both DACs are able to reduce noise to a level below a noise tolerance specified for the frequency distance, the DAC consuming the least power. To reduce the chip area required for the digital-to-analog conversion circuit, the first and second DACs advantageously have topologies that permit them to share common components (e.g., DAC unit elements).