mirror of https://github.com/lnis-uofu/SOFA.git
43 lines
1.5 KiB
ReStructuredText
43 lines
1.5 KiB
ReStructuredText
.. _sofa_chd_circuit_design:
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Circuit Designs
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---------------
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.. _sofa_chd_circuit_design_io:
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I/O Circuit
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^^^^^^^^^^^
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SOFA CHD FPGA share the same I/O circuit design as SOFA HD FPGA.
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See details at :ref:`sofa_hd_circuit_design_io`.
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.. _sofa_hd_circuit_design_mux:
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Multiplexer
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^^^^^^^^^^^
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Routing multiplexer are designed by using a few custom cells based on the Skywater *High-Density* (HD) PDK, as shown in :numref:`fig_sofa_chd_mux_circuit`.
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The multiplexer design follows a two-level structure, which is applied to all the routing multiplexers in logic elements, connection blocks and switch blocks across the FPGA fabric.
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.. _fig_sofa_chd_mux_circuit:
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.. figure:: ./figures/sofa_chd_mux_circuit.svg
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:scale: 30%
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:alt: Schematic of multiplexer design in SOFA CHD FPGA
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Schematic of multiplexer design in SOFA CHD FPGA
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Each primitive in the two-level structure could be a 2/3/4-input custom cell, depending on the input size of the routing multiplexer.
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Each custom cell is built with input inverters and transmission-gates.
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For instance, :numref:`fig_sofa_chd_custom_mux_cells` shows the transistor-level design of a 3-input custom cell.
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.. _fig_sofa_chd_custom_mux_cells:
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.. figure:: ./figures/custom_mux_cells.svg
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:scale: 40%
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:alt: Detailed schematic of a 3-input custom cell in SOFA CHD FPGA
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Detailed schematic of a 3-input custom cell in SOFA CHD FPGA
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.. note:: Each routing multiplexer has a dedicated input which is connected to ground (GND) signal. When it is not used, the output will be driven by the ground, working as a constant generator.
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