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| author | Jon Nordby <jononor@gmail.com> | 2025-08-09 00:01:44 +0200 |
|---|---|---|
| committer | Jon Nordby <jononor@gmail.com> | 2025-08-09 00:09:19 +0200 |
| commit | c479b10723a1a4a5ecbc6e69d3dcc6fc7c23e125 (patch) | |
| tree | 04f4d3538ec1a7056af26e7c5d969c90548d6924 | |
| parent | af24fc893090c12af3d8e2a16fb2d86267e0955a (diff) | |
pdm: Using 255 seems pretty nice
Lower values have much larger DC offsets on output
| -rw-r--r-- | bindings/test_galearn_pdm.py | 2 | ||||
| -rw-r--r-- | cocotb_try/cic3_pdm.v | 21 |
2 files changed, 10 insertions, 13 deletions
diff --git a/bindings/test_galearn_pdm.py b/bindings/test_galearn_pdm.py index 6fbbc4c..b55fc53 100644 --- a/bindings/test_galearn_pdm.py +++ b/bindings/test_galearn_pdm.py @@ -137,7 +137,7 @@ def test_dc(): out = numpy.zeros(shape=len(pdm_input)//DECIMATION, dtype=numpy.int16) # Process using filter - n_samples = galearn_pdm.process(pdm_input, out, 64, 0) + n_samples = galearn_pdm.process(pdm_input, out, 255, 0) out = out / (2**12) # Compensate for delay through filter diff --git a/cocotb_try/cic3_pdm.v b/cocotb_try/cic3_pdm.v index 3d23d44..9e96742 100644 --- a/cocotb_try/cic3_pdm.v +++ b/cocotb_try/cic3_pdm.v @@ -102,21 +102,18 @@ module cic3_pdm ( // Bypass DC removal pcm_out <= scaled_out; end else begin - // Calculate the updated accumulator value first - reg signed [19:0] new_accumulator; + // Simple leaky integrator with sign extension case (dc_alpha) - 8'd1: new_accumulator = dc_accumulator - (dc_accumulator >>> 12) + {{4{scaled_out[15]}}, scaled_out}; - 8'd16: new_accumulator = dc_accumulator - (dc_accumulator >>> 8) + {{4{scaled_out[15]}}, scaled_out}; - 8'd64: new_accumulator = dc_accumulator - (dc_accumulator >>> 6) + {{4{scaled_out[15]}}, scaled_out}; - 8'd255: new_accumulator = dc_accumulator - (dc_accumulator >>> 4) + {{4{scaled_out[15]}}, scaled_out}; - default: new_accumulator = dc_accumulator - (dc_accumulator >>> 8) + {{4{scaled_out[15]}}, scaled_out}; + 8'd1: dc_accumulator <= dc_accumulator - (dc_accumulator >>> 12) + {{4{scaled_out[15]}}, scaled_out}; + 8'd16: dc_accumulator <= dc_accumulator - (dc_accumulator >>> 8) + {{4{scaled_out[15]}}, scaled_out}; + 8'd64: dc_accumulator <= dc_accumulator - (dc_accumulator >>> 6) + {{4{scaled_out[15]}}, scaled_out}; + 8'd128: dc_accumulator <= dc_accumulator - (dc_accumulator >>> 5) + {{4{scaled_out[15]}}, scaled_out}; + 8'd255: dc_accumulator <= dc_accumulator - (dc_accumulator >>> 4) + {{4{scaled_out[15]}}, scaled_out}; + default: dc_accumulator <= dc_accumulator - (dc_accumulator >>> 8) + {{4{scaled_out[15]}}, scaled_out}; endcase - // Update accumulator - dc_accumulator <= new_accumulator; - - // Output = input - NEW DC estimate (not old one) - pcm_out <= scaled_out - new_accumulator[19:4]; + // Output = input - DC estimate (using OLD estimate to avoid combinational loop) + pcm_out <= scaled_out - dc_accumulator[19:4]; end pcm_valid <= 1; end |