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The RF signal output from the photodiode is amplified by 15 dB before passing through a custom 1300-1720 MHz bandpass antialiasing filter. A directional coupler follows this filter to inject a reference signal for calibrating ADC relative phase. The 50 $`\Omega`$ single-ended signal line is then converted with a balun to a 100 $`\Omega`$ differential pair compatible with the ADC inputs of the Xilinx ZCU216 RFSoC board.
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#### Single-Channel Receiver and Balun Board
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Single-channel RFoF receiver boards were fabricated to test performance of our circuit deigns and board layout up to the filter. The coupler and balun were not included for these test boards. A simplified schematic diagram and image of our most recent single-channel RX test board are shown below:
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<div align="center">
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<img src="../uploads/d6e1f2215c3dd280cbceffa325b2fb36/1_ch_RX_Schematic.PNG" width = "470"/>
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<img src="../uploads/56008a263b7cccf835381c18328a7bbe/IMG_0853.jpg" width = "470"/>
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Figure 1: Left: Simplified single-channel RFoF receiver schematic, Right: Single-channel RFoF receiver.
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</div>
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Single-channel RFoF receiver boards were fabricated to test performance of our circuit deigns and board layout up to the filter.
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To interface with the ZCU216 RFSoC we built a 16-channel balun board, with couplers for phase calibration signal injection included on each channel (see Fig. 2). With exception of the SMA connectors and T-lines to the couplers, the layout of this board is practically identical to post-bandpass-filter signal chain of the 16-channel RX boards we are developing. This allows us to characterize performance of all post-RX test board components and T-lines of the RFoF receiver sub-system. Using the single-channel RX test board in conjunction with the 16-channel balun board, we can characterize the full RX system performance.
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