| .. _analog_model: |
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|
| ######################### |
| Models of Analog Circuits |
| ######################### |
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| .. versionadded:: 1.6.0 |
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| This is the example :mod:`analog_model` showing how to use Python models |
| for analog circuits together with a digital part. |
| For an FPGA, these analog circuits would be implemented off-chip, |
| while for an ASIC, they would usually co-exist with the digital part on the same die. |
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| The Python model consists of an Analog Front-End (AFE) in file :file:`afe.py` containing |
| a Programmable Gain Amplifier (PGA) with a selectable gain of ``5.0`` and ``10.0``, |
| and a 13-bit Analog-to-Digital Converter (ADC) with a reference voltage of ``2.0 V``. |
| These analog models hand over data via a blocking :class:`cocotb.queue.Queue`. |
|
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| The digital part (in :file:`digital.sv`) |
| monitors the measurement value converted by the ADC |
| and selects the gain of the PGA based on the received value. |
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| A test :file:`test_analog_model.py` exercises these submodules. |
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| When running the example, you will get the following output: |
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| .. code-block:: none |
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| 0.00ns INFO ...test_analog_model.0x7ff913700490 decorators.py:313 in _advance Starting test: "test_analog_model" |
| Description: Exercise an Analog Front-end and its digital controller. |
| 1001.00ns INFO cocotb.digital test_analog_model.py:55 in test_analog_model AFE converted input value 0.1V to 2047 |
| 3000.00ns (digital) HDL got meas_val=2047 (0x07ff) |
| 3000.00ns (digital) PGA gain select was 0 --> calculated AFE input value back to 0.099963 |
| 3000.00ns (digital) Measurement value is less than 30% of max, switching PGA gain from 5.0 to 10.0 |
| 7301.00ns INFO cocotb.digital test_analog_model.py:55 in test_analog_model AFE converted input value 0.1V to 4095 |
| 9000.00ns (digital) HDL got meas_val=4095 (0x0fff) |
| 9000.00ns (digital) PGA gain select was 1 --> calculated AFE input value back to 0.099988 |
| 13301.00ns INFO cocotb.digital test_analog_model.py:55 in test_analog_model AFE converted input value 0.0V to 0 |
| 15000.00ns (digital) HDL got meas_val=0 (0x0000) |
| 15000.00ns (digital) PGA gain select was 1 --> calculated AFE input value back to 0.000000 |
| Saturating measurement value 10238 to [0:8191]! |
| 19301.00ns INFO cocotb.digital test_analog_model.py:55 in test_analog_model AFE converted input value 0.25V to 8191 |
| 21000.00ns (digital) HDL got meas_val=8191 (0x1fff) |
| 21000.00ns (digital) PGA gain select was 1 --> calculated AFE input value back to 0.200000 |
| 21000.00ns (digital) Measurement value is more than 70% of max, switching PGA gain from 10.0 to 5.0 |
| 25301.00ns INFO cocotb.digital test_analog_model.py:55 in test_analog_model AFE converted input value 0.25V to 5119 |
| 27000.00ns (digital) HDL got meas_val=5119 (0x13ff) |
| 27000.00ns (digital) PGA gain select was 0 --> calculated AFE input value back to 0.249982 |
| 30301.00ns INFO cocotb.regression regression.py:364 in _score_test Test Passed: test_analog_model |
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| You can view the source code of the example by clicking the file names below. |
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| .. details:: :file:`afe.py` |
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| .. literalinclude:: ../../examples/analog_model/afe.py |
| :language: python |
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| .. details:: :file:`digital.sv` |
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| .. literalinclude:: ../../examples/analog_model/digital.sv |
| :language: systemverilog |
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| .. details:: :file:`test_analog_model.py` |
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| .. literalinclude:: ../../examples/analog_model/test_analog_model.py |
| :language: python |
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| .. details:: :file:`Makefile` |
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| .. literalinclude:: ../../examples/analog_model/Makefile |
| :language: make |
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|
