diff options
| -rw-r--r-- | bindings/test_galearn_pdm.py | 10 | ||||
| -rw-r--r-- | cocotb_try/cic3_pdm.v | 42 |
2 files changed, 30 insertions, 22 deletions
diff --git a/bindings/test_galearn_pdm.py b/bindings/test_galearn_pdm.py index 3a19762..6274868 100644 --- a/bindings/test_galearn_pdm.py +++ b/bindings/test_galearn_pdm.py @@ -126,19 +126,19 @@ def test_dc(): function = sys._getframe().f_code.co_name # looks up function name test_name = f'{function}' sr = SAMPLERATE_DEFAULT - test_duration = 0.0013 + test_duration = 0.030 # Generate test data frequency = 1000 pcm_input = generate_test_tone(duration_sec=test_duration, - freqs=[frequency], noise_level=0.0, sample_rate=sr, amplitude=0.01, - ) + 0.10 # DC + freqs=[frequency], noise_level=0.0, sample_rate=sr, amplitude=0.1, + ) + 0.20 # DC pdm_input = convert(pcm_input) out = numpy.zeros(shape=len(pdm_input)//DECIMATION, dtype=numpy.int16) # Process using filter - n_samples = galearn_pdm.process(pdm_input, out, 200, 1) - out = out / (2**15) # XXX: where does this magical come from? + n_samples = galearn_pdm.process(pdm_input, out, 128, 5) + out = out / (2**12) # Compensate for delay through filter delay = find_forward_shift(pcm_input, out) diff --git a/cocotb_try/cic3_pdm.v b/cocotb_try/cic3_pdm.v index 4e8d664..c53e867 100644 --- a/cocotb_try/cic3_pdm.v +++ b/cocotb_try/cic3_pdm.v @@ -25,17 +25,23 @@ module cic3_pdm ( reg signed [15:0] scaled_out; reg cic_valid; - // HPF registers - reg signed [15:0] hpf_x_prev; - reg signed [15:0] hpf_y_prev; + // Leaky integrator HPF registers + reg signed [23:0] hpf_integrator; // 24-bit for precision + reg signed [15:0] hpf_output; // HPF calculation wires + wire signed [8:0] hpf_complement; + wire signed [23:0] hpf_scaled_input; + wire signed [23:0] hpf_dc_estimate; /* verilator lint_off UNUSEDSIGNAL */ - wire signed [23:0] hpf_temp; + wire signed [23:0] hpf_temp_result; /* verilator lint_on UNUSEDSIGNAL */ - wire signed [15:0] hpf_calc; - // Convert 1-bit PDM to signed + // HPF wire assignments + assign hpf_complement = 9'd256 - {1'b0, hpf_alpha}; + assign hpf_scaled_input = {{8{scaled_out[15]}}, scaled_out}; + assign hpf_dc_estimate = hpf_integrator >>> 8; + assign hpf_temp_result = hpf_scaled_input - hpf_dc_estimate; wire signed [CIC_WIDTH-1:0] pdm_signed = pdm_in ? 17'sd1 : -17'sd1; // CIC Integrator stages (run at PDM rate) @@ -95,15 +101,13 @@ module cic3_pdm ( endcase end - // HPF calculation - assign hpf_temp = ((hpf_alpha * hpf_y_prev) + (({8'd0, scaled_out} - {8'd0, hpf_x_prev}) << 8)) >>> 8; - assign hpf_calc = hpf_temp[15:0]; - - // High-pass filter (1st order IIR: y[n] = alpha/256 * y[n-1] + (x[n] - x[n-1])) + // Leaky integrator-based DC blocker + // y[n] = x[n] - dc_estimate + // dc_estimate[n] = alpha/256 * dc_estimate[n-1] + (1-alpha/256) * x[n] always @(posedge clk) begin if (rst) begin - hpf_x_prev <= 0; - hpf_y_prev <= 0; + hpf_integrator <= 0; + hpf_output <= 0; pcm_out <= 0; pcm_valid <= 0; end else begin @@ -114,10 +118,14 @@ module cic3_pdm ( // Bypass HPF completely pcm_out <= scaled_out; end else begin - // HPF computation: y[n] = alpha/256 * y[n-1] + (x[n] - x[n-1]) - pcm_out <= hpf_calc; - hpf_x_prev <= scaled_out; - hpf_y_prev <= hpf_calc; + // Update leaky integrator (DC estimate) + // integrator = alpha * integrator + (256-alpha) * input + hpf_integrator <= (hpf_alpha * hpf_dc_estimate) + + (hpf_complement * hpf_scaled_input); + + // Output = input - DC estimate + hpf_output <= hpf_temp_result[15:0]; + pcm_out <= hpf_output; end pcm_valid <= 1; end |