Mixed-Mode Time-Interleaved DAC for RF Bandwidth and Image Control
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Solution Overview
Problem
Digital-to-analog converters (DACs) for radio-frequency (RF) applications face limitations in bandwidth, leading to band-limited frequency responses and spurious emission issues, which reduce dynamic range and complicate signal replication, especially when operating near the Nyquist frequency.
Innovation Solution
A digital-to-analog converter (DAC) system that includes an upsampling circuit, a finite impulse response (FIR) filter, and a time-interleaved DAC (TIDAC) configuration, which performs mixing operations in either the digital or analog domain to increase bandwidth and reduce or remove image artifacts within the RF signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional DAC is used for RF applications, then the device is simple to implement, but the bandwidth is limited and spurious emissions occur
Solution Approach 1:
The DAC is divided into multiple parallel sub-DACs (e.g., two sub-DACs) that operate simultaneously with different sampling rates. Each sub-DAC processes a portion of the digital signal, and their analog outputs are combined through mixing and summing operations. This segmentation allows the overall system to achieve extended bandwidth beyond what a single DAC could provide, while managing complexity through modular architecture.
Solution Approach 2:
The patent extends the bandwidth by introducing a time-interleaved dimension with multiple sub-DACs operating at different sampling rates. By utilizing multiple time domains and combining them through frequency mixing, the system achieves bandwidth extension in the frequency dimension without requiring a single ultra-high-speed DAC, thus managing complexity differently.
2Length of moving object
If the DAC operates near the Nyquist frequency, then the bandwidth is maximized, but spurious emissions and image artifacts increase
Solution Approach 1:
The harmful image artifacts generated by each sub-DAC are extracted and removed through frequency mixing operations. The mixing process shifts the images to different frequency locations where they can be filtered out, while the desired signal components are retained and summed. This extraction and removal of harmful artifacts allows the system to operate near Nyquist frequency without suffering from excessive spurious emissions.
Solution Approach 2:
The patent converts the harmful image artifacts into a useful feature by deliberately generating controlled images through time-interleaved operation, then using frequency mixing to position these images in predictable locations. This allows for effective filtering while maintaining the bandwidth benefits of operating near Nyquist frequency. The harmful images become predictable byproducts that can be managed rather than random disturbances.
3Length of moving object
If multiple time-interleaved sub-DACs are used to increase bandwidth, then the bandwidth is extended, but the device complexity increases
Solution Approach 1:
Multiple sub-DAC outputs are merged through analog mixing and summing operations. The mixing stage combines the time-interleaved signals while the summing stage integrates them into a single output. This merging approach allows bandwidth extension through parallel processing while consolidating the multiple outputs into one unified signal, managing the complexity of having multiple sub-DACs.
Solution Approach 2:
The mixing circuit performs multiple functions simultaneously: it frequency-shifts the sub-DAC outputs, removes image artifacts, and prepares signals for summation. This multi-functionality reduces the need for separate dedicated circuits for each operation, thereby managing overall device complexity while achieving bandwidth extension through time-interleaved architecture.
Data Source
AI summary
Disclosed are systems, devices and methods related to mixed mode time interleaved digital-to-analog converters (DACs). In some embodiments, such DACs can be utilized for radio-frequency (RF) applications. In some embodiments, a DAC for RF applications can include a first circuit configured to receive a digital signal and perform a first operation to yield an increased bandwidth of the DAC. The DAC can further include a second circuit configured to perform a second operation on the digital signal to yield an analog signal representative of the digital signal. The second circuit can be further configured to reduce or remove an image within the increased bandwidth.