Interleaved Sigma-Delta Modulator for Wideband SDR Transmission
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Solution Overview
Problem
Current RF transmitters face limitations in achieving wide-band operation with fast switching due to constraints in sampling clock rates, leading to limited dynamic range and reconfigurability, especially in multi-mode and multi-band applications.
Innovation Solution
An interleaved delta-sigma modulator architecture that includes interleaved filter banks, a DEM network, and arrays of DACs, which allows for time-interleaving and dynamic element matching to reduce mismatch errors and achieve high-dynamic-range operation without requiring high sampling clock rates, enabling flexible band switching and improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single delta-sigma modulator is used, then the structure is simple, but the dynamic range and bandwidth are limited due to moderate clock frequency
Solution Approach 1:
The single modulator is segmented into multiple parallel modulators (first and second delta-sigma modulators) operating at different clock frequencies. Each modulator handles a portion of the signal, with the first operating at a lower clock frequency and the second at a higher clock frequency, collectively achieving both simplicity and high dynamic range
2Device complexity
If a single delta-sigma modulator is used, then the design is straightforward, but the bandwidth is limited
Solution Approach 1:
The bandwidth limitation is resolved by segmenting the signal processing into multiple parallel modulators with different clock frequencies. The first modulator operates at a moderate clock frequency for baseline processing, while the second operates at a higher clock frequency to extend the overall bandwidth capability
Solution Approach 2:
The system transitions from a single-dimension (single clock frequency) approach to a multi-dimensional approach by introducing modulators operating at different clock frequency dimensions. This allows the system to achieve extended bandwidth without proportionally increasing the complexity of each individual modulator
3Speed
If time-interleaved DACs are used, then bandwidth is improved, but LO switching time and filter components limit reconfigurability
Solution Approach 1:
The system implements dynamic reconfigurability by allowing the digital signal processing unit to programmatically control the filter coefficients and modulation parameters. This enables the transmitter to be reconfigured for different frequency bands and modes without physical hardware changes, overcoming the limitations of fixed RF filter components
4Manufacturing precision
If LO based transmitters are used, then frequency synthesis is achieved, but channel switching time is too long for agile radio applications
Solution Approach 1:
The patent replaces the traditional LO-based frequency synthesis mechanism with a digitally-driven approach. The digital signal processing unit generates baseband signals that are directly modulated, eliminating the need for LO tuning and frequency synthesis hardware. This substitution reduces channel switching time from microsecond levels to nanosecond levels, enabling agile radio applications
Data Source
AI summary
A Delta-Sigma modulator architecture is disclosed that uses interleaving and dynamic matching algorithms to address the needs of multi-mode, multi-band high bandwidth transmitters. The proposed architecture also supports a novel software defined transmitter architecture based on an interleaved Delta-Sigma modulator to generate RF signals. The proposed architecture leverages interleaving concepts to relax subcomponent clock rates without changing the effective oversampling ratio, thus, making it easier to reach aggressive dynamic range goals across wider bandwidths at higher frequencies. The DEM algorithm helps to randomize mismatch errors across all interleaved paths and improves substantially the signal-to-noise ratio. Additionally, a tunable bandpass filter can be added to reject out-of-band emissions.