diff --git a/cores/primitive/lvds_comparator/lvds_comparator.core b/cores/primitive/lvds_comparator/lvds_comparator.core
new file mode 100644
index 0000000..efb8098
--- /dev/null
+++ b/cores/primitive/lvds_comparator/lvds_comparator.core
@@ -0,0 +1,26 @@
+CAPI=2:
+
+name: joppeb:primitive:lvds_comparator:1.0
+description: LVDS comparator wrapper
+
+filesets:
+    wrapper:
+        files:
+            - lvds_comparator.v
+        file_type: verilogSource
+    generic:
+        files:
+            - lvds_comparator_generic_impl.v
+        file_type: verilogSource
+    spartan6:
+        files:
+            - lvds_comparator_spartan6.v
+        file_type: verilogSource
+
+targets:
+    default:
+        filesets:
+            - wrapper
+            - generic
+            - spartan6
+        toplevel: lvds_comparator
diff --git a/cores/primitive/lvds_comparator/lvds_comparator.v b/cores/primitive/lvds_comparator/lvds_comparator.v
new file mode 100644
index 0000000..b3076e4
--- /dev/null
+++ b/cores/primitive/lvds_comparator/lvds_comparator.v
@@ -0,0 +1,19 @@
+module lvds_comparator(
+    input wire a,
+    input wire b,
+    output wire o
+);
+`ifdef FPGA_SPARTAN6
+    lvds_comparator_spartan6_impl impl_i (
+        .a(a),
+        .b(b),
+        .o(o)
+    );
+`else
+    lvds_comparator_generic_impl impl_i (
+        .a(a),
+        .b(b),
+        .o(o)
+    );
+`endif
+endmodule
\ No newline at end of file
diff --git a/cores/primitive/lvds_comparator/lvds_comparator_generic_impl.v b/cores/primitive/lvds_comparator/lvds_comparator_generic_impl.v
new file mode 100644
index 0000000..2c495a2
--- /dev/null
+++ b/cores/primitive/lvds_comparator/lvds_comparator_generic_impl.v
@@ -0,0 +1,7 @@
+module lvds_comparator_generic_impl (
+    input wire a,
+    input wire b,
+    output wire o
+);
+    assign o = a;
+endmodule
\ No newline at end of file
diff --git a/cores/primitive/lvds_comparator/lvds_comparator_spartan6.v b/cores/primitive/lvds_comparator/lvds_comparator_spartan6.v
new file mode 100644
index 0000000..2eeaa04
--- /dev/null
+++ b/cores/primitive/lvds_comparator/lvds_comparator_spartan6.v
@@ -0,0 +1,14 @@
+module lvds_comparator_spartan6_impl (
+    input wire a,
+    input wire b,
+    output wire o
+);
+    IBUFDS #(
+        .DIFF_TERM("FALSE"),
+        .IOSTANDARD("LVDS33")
+    ) lvds_buf (
+        .O(o),
+        .I(a),
+        .IB(b)
+    );
+endmodule
\ No newline at end of file
diff --git a/cores/signal/decimate_by_r_q15.v/decimate_by_r_q15.core b/cores/signal/decimate_by_r_q15.v/decimate_by_r_q15.core
new file mode 100644
index 0000000..418144c
--- /dev/null
+++ b/cores/signal/decimate_by_r_q15.v/decimate_by_r_q15.core
@@ -0,0 +1,29 @@
+CAPI=2:
+
+name: joppeb:signal:decimate_by_r_q15:1.0
+description: Q1.15 integer-rate decimator
+
+filesets:
+    rtl:
+        files:
+            - decimate_by_r_q15.v
+        file_type: verilogSource
+
+targets:
+    default:
+        filesets:
+            - rtl
+        toplevel: decimate_by_r_q15
+        parameters:
+            - R
+            - CNT_W
+
+parameters:
+    R:
+        datatype: int
+        description: Integer decimation ratio
+        paramtype: vlogparam
+    CNT_W:
+        datatype: int
+        description: Counter width for the decimation counter
+        paramtype: vlogparam
diff --git a/cores/signal/decimate_by_r_q15.v/decimate_by_r_q15.v b/cores/signal/decimate_by_r_q15.v/decimate_by_r_q15.v
new file mode 100644
index 0000000..49aedeb
--- /dev/null
+++ b/cores/signal/decimate_by_r_q15.v/decimate_by_r_q15.v
@@ -0,0 +1,74 @@
+`timescale 1ns/1ps
+
+// =============================================================================
+// Decimator by R
+// Reduces the effective sample rate by an integer factor R by selecting every
+// R-th input sample. Generates a one-cycle 'o_valid' pulse each time a new
+// decimated sample is produced.
+//
+// Implements:
+//      For each valid input sample:
+//          if (count == R-1):
+//              count     <= 0
+//              o_q15   <= i_q15
+//              o_valid <= 1
+//          else:
+//              count     <= count + 1
+//
+// parameters:
+//      -- R      : integer decimation factor (e.g., 400)
+//                   output sample rate = input rate / R
+//      -- CNT_W  : counter bit width, must satisfy 2^CNT_W > R
+//
+// inout:
+//      -- i_clk     : input clock (same rate as 'i_valid')
+//      -- i_rst_n   : active-low synchronous reset
+//      -- i_valid   : input data strobe; assert 1'b1 if input is always valid
+//      -- i_q15     : signed 16-bit Q1.15 input sample (full-rate)
+//      -- o_valid   : single-cycle pulse every R samples (decimated rate strobe)
+//      -- o_q15     : signed 16-bit Q1.15 output sample (decimated stream)
+//
+// Notes:
+//  - This module performs *pure downsampling* (sample selection only).
+//    It does not include any anti-alias filtering; high-frequency content
+//    above the new Nyquist limit (Fs_out / 2) will alias into the baseband.
+//  - For most applications, an anti-alias low-pass filter such as
+//    lpf_iir_q15 or a FIR stage should precede this decimator.
+//  - The output sample rate is given by:
+//          Fs_out = Fs_in / R
+//  - Typical usage: interface between high-rate sigma-delta or oversampled
+//    data streams and lower-rate processing stages.
+// =============================================================================
+module decimate_by_r_q15 #(
+    parameter integer R      = 400, // decimation factor
+    parameter integer CNT_W  = 10   // width so that 2^CNT_W > R (e.g., 10 for 750)
+)(
+    input  wire        i_clk,
+    input  wire        i_rst_n,
+    input  wire        i_valid,          // assert 1'b1 if always valid
+    input  wire signed [15:0] i_q15,     // Q1.15 sample at full rate
+    output reg         o_valid,          // 1-cycle pulse every R samples
+    output reg  signed [15:0] o_q15      // Q1.15 sample at decimated rate
+);
+    reg [CNT_W-1:0] cnt;
+
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n) begin
+            cnt       <= {CNT_W{1'b0}};
+            o_valid   <= 1'b0;
+            o_q15     <= 16'sd0;
+        end else begin
+            o_valid <= 1'b0;
+
+            if (i_valid) begin
+                if (cnt == R-1) begin
+                    cnt       <= {CNT_W{1'b0}};
+                    o_q15     <= i_q15;
+                    o_valid   <= 1'b1;
+                end else begin
+                    cnt <= cnt + 1'b1;
+                end
+            end
+        end
+    end
+endmodule
diff --git a/cores/signal/lpf_iir_q15_k/lpf_iir_q15_k.core b/cores/signal/lpf_iir_q15_k/lpf_iir_q15_k.core
new file mode 100644
index 0000000..b134b5d
--- /dev/null
+++ b/cores/signal/lpf_iir_q15_k/lpf_iir_q15_k.core
@@ -0,0 +1,24 @@
+CAPI=2:
+
+name: joppeb:signal:lpf_iir_q15_k:1.0
+description: First-order Q1.15 IIR low-pass filter
+
+filesets:
+    rtl:
+        files:
+            - lpf_iir_q15_k.v
+        file_type: verilogSource
+
+targets:
+    default:
+        filesets:
+            - rtl
+        toplevel: lpf_iir_q15_k
+        parameters:
+            - K
+
+parameters:
+    K:
+        datatype: int
+        description: Filter shift factor
+        paramtype: vlogparam
diff --git a/cores/signal/lpf_iir_q15_k/lpf_iir_q15_k.v b/cores/signal/lpf_iir_q15_k/lpf_iir_q15_k.v
new file mode 100644
index 0000000..bfcaaa0
--- /dev/null
+++ b/cores/signal/lpf_iir_q15_k/lpf_iir_q15_k.v
@@ -0,0 +1,64 @@
+`timescale 1ns/1ps
+
+// =============================================================================
+// Low-Pass IIR Filter (Q1.15)
+// Simple first-order infinite impulse response filter, equivalent to an
+// exponential moving average. Provides an adjustable smoothing factor based
+// on parameter K.
+//
+// Implements:
+//      Y[n+1] = Y[n] + (X[n] - Y[n]) / 2^K
+//
+// This is a purely digital one-pole low-pass filter whose time constant
+// approximates that of an analog RC filter, where alpha = 1 / 2^K.
+//
+// The larger K is, the slower the filter responds (stronger smoothing).
+// The smaller K is, the faster it reacts to changes.
+//
+// parameters:
+//      -- K : filter shift factor (integer, 4..14 typical)
+//              cutoff frequency ≈ Fs / (2π * 2^K)
+//              larger K → lower cutoff
+//
+// inout:
+//      -- i_clk   : input clock
+//      -- i_rst_n : active-low reset
+//      -- i_x_q15 : signed 16-bit Q1.15 input sample (e.g., 0..0x7FFF)
+//      -- o_y_q15 : signed 16-bit Q1.15 filtered output
+//
+// Notes:
+//  - The arithmetic right shift implements division by 2^K.
+//  - Internal arithmetic is Q1.15 fixed-point with saturation
+//    to [0, 0x7FFF] (for non-negative signals).
+//  - Useful for smoothing noisy ADC / sigma-delta data streams
+//    or modeling an RC envelope follower.
+// =============================================================================
+module lpf_iir_q15_k #( 
+    parameter integer K = 10 // try 8..12; bigger = more smoothing 
+)( 
+    input wire i_clk, 
+    input wire i_rst_n, 
+    input wire signed [15:0] i_x_q15, // Q1.15 input (e.g., 0..0x7FFF) 
+    output reg signed [15:0] o_y_q15 // Q1.15 output 
+); 
+    wire signed [15:0] e_q15 = i_x_q15 - o_y_q15; 
+    wire signed [15:0] delta_q15 = e_q15 >>> K; // arithmetic shift 
+    wire signed [15:0] y_next = o_y_q15 + delta_q15; // clamp to [0, 0x7FFF] (handy if your signal is non-negative) 
+    
+    function signed [15:0] clamp01; 
+        input signed [15:0] v; 
+    begin
+        if (v < 16'sd0) 
+            clamp01 = 16'sd0; 
+        else if (v > 16'sh7FFF) 
+            clamp01 = 16'sh7FFF; 
+        else 
+            clamp01 = v; 
+        end 
+    endfunction 
+    
+    always @(posedge i_clk or negedge i_rst_n) begin 
+        if (!i_rst_n) o_y_q15 <= 16'sd0; 
+        else o_y_q15 <= clamp01(y_next); 
+    end 
+endmodule
diff --git a/cores/signal/nco_q15/rtl/nco_q15.v b/cores/signal/nco_q15/rtl/nco_q15.v
index fe20395..13c6bb4 100644
--- a/cores/signal/nco_q15/rtl/nco_q15.v
+++ b/cores/signal/nco_q15/rtl/nco_q15.v
@@ -8,23 +8,23 @@
 //      -- CLK_HZ : input clock frequency in Hz
 //      -- FS_HZ : output sample frequency in Hz
 // inout:
-//      -- clk : input clock
-//      -- rst_n : reset
-//      -- freq_hz : decimal number of desired generated frequency in Hz, 0-FS/2
-//      -- sin_q15/cos_q15 : I and Q outputs
-//      -- clk_en : output valid strobe
+//      -- i_clk : input clock
+//      -- i_rst_n : reset
+//      -- i_freq_hz : decimal number of desired generated frequency in Hz, 0-FS/2
+//      -- o_sin_q15/o_cos_q15 : I and Q outputs
+//      -- o_clk_en : output valid strobe
 // =============================================================================
 module nco_q15 #(
     parameter integer CLK_HZ = 120_000_000,         // input clock
     parameter integer FS_HZ = 40_000                // sample rate
 )(
-    input wire clk,                                 // CLK_HZ domain
-    input wire rst_n,                               // async active-low reset
-    input wire [31:0] freq_hz,                      // desired output frequency (Hz), 0..FS_HZ/2
+    input wire i_clk,                               // CLK_HZ domain
+    input wire i_rst_n,                             // async active-low reset
+    input wire [31:0] i_freq_hz,                    // desired output frequency (Hz), 0..FS_HZ/2
 
-    output reg signed [15:0] sin_q15,               // Q1.15 sine
-    output reg signed [15:0] cos_q15,               // Q1.15 cosine
-    output reg clk_en                               // 1-cycle strobe @ FS_HZ
+    output reg signed [15:0] o_sin_q15,             // Q1.15 sine
+    output reg signed [15:0] o_cos_q15,             // Q1.15 cosine
+    output reg o_clk_en                             // 1-cycle strobe @ FS_HZ
 );
     localparam integer PHASE_FRAC_BITS = 6;
     localparam integer QTR_ADDR_BITS = 6;
@@ -41,17 +41,17 @@ module nco_q15 #(
     endfunction
 
     reg [clog2(DIV)-1:0] tick_cnt;
-    always @(posedge clk or negedge rst_n) begin
-        if (!rst_n) begin tick_cnt <= 0; clk_en <= 1'b0; end
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n) begin tick_cnt <= 0; o_clk_en <= 1'b0; end
         else begin
-        clk_en <= 1'b0;
-        if (tick_cnt == DIV-1) begin tick_cnt <= 0; clk_en <= 1'b1; end
+        o_clk_en <= 1'b0;
+        if (tick_cnt == DIV-1) begin tick_cnt <= 0; o_clk_en <= 1'b1; end
         else tick_cnt <= tick_cnt + 1'b1;
         end
     end
 
-    // 32-cycle shift-add multiply: prod = freq_hz * RECIP  (no multiplications themself)
-	// Starts at clk_en, finishes in 32 cycles (<< available cycles per sample).
+    // 32-cycle shift-add multiply: prod = i_freq_hz * RECIP  (no multiplications themself)
+	// Starts at o_clk_en, finishes in 32 cycles (<< available cycles per sample).
     reg        mul_busy;
     reg  [5:0] mul_i;           // 0..31
     reg [31:0] f_reg;
@@ -59,15 +59,15 @@ module nco_q15 #(
 
     wire [95:0] recip_shift = {{32{1'b0}}, RECIP} << mul_i; // shift constant by i
 
-    always @(posedge clk or negedge rst_n) begin
-        if (!rst_n) begin
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n) begin
         mul_busy <= 1'b0; mul_i <= 6'd0; f_reg <= 32'd0; acc <= 96'd0;
         end else begin
-        if (clk_en && !mul_busy) begin
+        if (o_clk_en && !mul_busy) begin
             // kick off a new multiply this sample
             mul_busy <= 1'b1;
             mul_i    <= 6'd0;
-            f_reg    <= (freq_hz > (FS_HZ>>1)) ? (FS_HZ>>1) : freq_hz; // clamp to Nyquist
+            f_reg    <= (i_freq_hz > (FS_HZ>>1)) ? (FS_HZ>>1) : i_freq_hz; // clamp to Nyquist
             acc      <= 96'd0;
         end else if (mul_busy) begin
             // add shifted RECIP if bit is set
@@ -86,16 +86,16 @@ module nco_q15 #(
     wire [95:0] acc_round = acc + (96'd1 << (SHIFT-1));
     wire [PHASE_BITS-1:0] ftw_next = acc_round[SHIFT +: PHASE_BITS]; // >> SHIFT
 
-    always @(posedge clk or negedge rst_n) begin
-        if (!rst_n) ftw_q <= {PHASE_BITS{1'b0}};
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n) ftw_q <= {PHASE_BITS{1'b0}};
         else if (!mul_busy) ftw_q <= ftw_next; // update once product ready
     end
 
     // Phase accumulator (advance at FS_HZ)
     reg [PHASE_BITS-1:0] phase;
-    always @(posedge clk or negedge rst_n) begin
-        if (!rst_n)      phase <= {PHASE_BITS{1'b0}};
-        else if (clk_en) phase <= phase + ftw_q;
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n)        phase <= {PHASE_BITS{1'b0}};
+        else if (o_clk_en) phase <= phase + ftw_q;
     end
 
     // Cosine phase = sine phase + 90°
@@ -113,8 +113,8 @@ module nco_q15 #(
 
     // 64-entry quarter-wave LUT
     wire [7:0] mag_sin_u8, mag_cos_u8;
-    sine_qtr_lut64 u_lut_s (.addr(idx_sin), .dout(mag_sin_u8));
-    sine_qtr_lut64 u_lut_c (.addr(idx_cos), .dout(mag_cos_u8));
+    sine_qtr_lut64 u_lut_s (.i_addr(idx_sin), .o_dout(mag_sin_u8));
+    sine_qtr_lut64 u_lut_c (.i_addr(idx_cos), .o_dout(mag_cos_u8));
 
     // Scale to Q1.15 and apply sign
     wire signed [15:0] mag_sin_q15 = {1'b0, mag_sin_u8, 7'd0};
@@ -125,39 +125,39 @@ module nco_q15 #(
     wire signed [15:0] sin_next = sin_neg ? -mag_sin_q15 : mag_sin_q15;
     wire signed [15:0] cos_next = cos_neg ? -mag_cos_q15 : mag_cos_q15;
 
-    always @(posedge clk or negedge rst_n) begin
-        if (!rst_n) begin
-        sin_q15 <= 16'sd0; cos_q15 <= 16'sd0;
-        end else if (clk_en) begin
-        sin_q15 <= sin_next; cos_q15 <= cos_next;
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n) begin
+        o_sin_q15 <= 16'sd0; o_cos_q15 <= 16'sd0;
+        end else if (o_clk_en) begin
+        o_sin_q15 <= sin_next; o_cos_q15 <= cos_next;
         end
     end
 
 endmodule
 	
 module sine_qtr_lut64(
-    input wire [5:0] addr,
-    output reg [7:0] dout
+    input wire [5:0] i_addr,
+    output reg [7:0] o_dout
 );
     always @* begin
-        case (addr)
-            6'd0: dout = 8'd0;    6'd1: dout = 8'd6;    6'd2: dout = 8'd13;   6'd3: dout = 8'd19;
-            6'd4: dout = 8'd25;   6'd5: dout = 8'd31;   6'd6: dout = 8'd37;   6'd7: dout = 8'd44;
-            6'd8: dout = 8'd50;   6'd9: dout = 8'd56;   6'd10: dout = 8'd62;  6'd11: dout = 8'd68;
-            6'd12: dout = 8'd74;  6'd13: dout = 8'd80;  6'd14: dout = 8'd86;  6'd15: dout = 8'd92;
-            6'd16: dout = 8'd98;  6'd17: dout = 8'd103; 6'd18: dout = 8'd109; 6'd19: dout = 8'd115;
-            6'd20: dout = 8'd120; 6'd21: dout = 8'd126; 6'd22: dout = 8'd131; 6'd23: dout = 8'd136;
-            6'd24: dout = 8'd142; 6'd25: dout = 8'd147; 6'd26: dout = 8'd152; 6'd27: dout = 8'd157;
-            6'd28: dout = 8'd162; 6'd29: dout = 8'd167; 6'd30: dout = 8'd171; 6'd31: dout = 8'd176;
-            6'd32: dout = 8'd180; 6'd33: dout = 8'd185; 6'd34: dout = 8'd189; 6'd35: dout = 8'd193;
-            6'd36: dout = 8'd197; 6'd37: dout = 8'd201; 6'd38: dout = 8'd205; 6'd39: dout = 8'd208;
-            6'd40: dout = 8'd212; 6'd41: dout = 8'd215; 6'd42: dout = 8'd219; 6'd43: dout = 8'd222;
-            6'd44: dout = 8'd225; 6'd45: dout = 8'd228; 6'd46: dout = 8'd231; 6'd47: dout = 8'd233;
-            6'd48: dout = 8'd236; 6'd49: dout = 8'd238; 6'd50: dout = 8'd240; 6'd51: dout = 8'd242;
-            6'd52: dout = 8'd244; 6'd53: dout = 8'd246; 6'd54: dout = 8'd247; 6'd55: dout = 8'd249;
-            6'd56: dout = 8'd250; 6'd57: dout = 8'd251; 6'd58: dout = 8'd252; 6'd59: dout = 8'd253;
-            6'd60: dout = 8'd254; 6'd61: dout = 8'd254; 6'd62: dout = 8'd255; 6'd63: dout = 8'd255;
-            default: dout=8'd0;
+        case (i_addr)
+            6'd0: o_dout = 8'd0;    6'd1: o_dout = 8'd6;    6'd2: o_dout = 8'd13;   6'd3: o_dout = 8'd19;
+            6'd4: o_dout = 8'd25;   6'd5: o_dout = 8'd31;   6'd6: o_dout = 8'd37;   6'd7: o_dout = 8'd44;
+            6'd8: o_dout = 8'd50;   6'd9: o_dout = 8'd56;   6'd10: o_dout = 8'd62;  6'd11: o_dout = 8'd68;
+            6'd12: o_dout = 8'd74;  6'd13: o_dout = 8'd80;  6'd14: o_dout = 8'd86;  6'd15: o_dout = 8'd92;
+            6'd16: o_dout = 8'd98;  6'd17: o_dout = 8'd103; 6'd18: o_dout = 8'd109; 6'd19: o_dout = 8'd115;
+            6'd20: o_dout = 8'd120; 6'd21: o_dout = 8'd126; 6'd22: o_dout = 8'd131; 6'd23: o_dout = 8'd136;
+            6'd24: o_dout = 8'd142; 6'd25: o_dout = 8'd147; 6'd26: o_dout = 8'd152; 6'd27: o_dout = 8'd157;
+            6'd28: o_dout = 8'd162; 6'd29: o_dout = 8'd167; 6'd30: o_dout = 8'd171; 6'd31: o_dout = 8'd176;
+            6'd32: o_dout = 8'd180; 6'd33: o_dout = 8'd185; 6'd34: o_dout = 8'd189; 6'd35: o_dout = 8'd193;
+            6'd36: o_dout = 8'd197; 6'd37: o_dout = 8'd201; 6'd38: o_dout = 8'd205; 6'd39: o_dout = 8'd208;
+            6'd40: o_dout = 8'd212; 6'd41: o_dout = 8'd215; 6'd42: o_dout = 8'd219; 6'd43: o_dout = 8'd222;
+            6'd44: o_dout = 8'd225; 6'd45: o_dout = 8'd228; 6'd46: o_dout = 8'd231; 6'd47: o_dout = 8'd233;
+            6'd48: o_dout = 8'd236; 6'd49: o_dout = 8'd238; 6'd50: o_dout = 8'd240; 6'd51: o_dout = 8'd242;
+            6'd52: o_dout = 8'd244; 6'd53: o_dout = 8'd246; 6'd54: o_dout = 8'd247; 6'd55: o_dout = 8'd249;
+            6'd56: o_dout = 8'd250; 6'd57: o_dout = 8'd251; 6'd58: o_dout = 8'd252; 6'd59: o_dout = 8'd253;
+            6'd60: o_dout = 8'd254; 6'd61: o_dout = 8'd254; 6'd62: o_dout = 8'd255; 6'd63: o_dout = 8'd255;
+            default: o_dout=8'd0;
         endcase
     end
-endmodule
\ No newline at end of file
+endmodule
diff --git a/cores/signal/nco_q15/tb/tb_nco_q15.v b/cores/signal/nco_q15/tb/tb_nco_q15.v
index a85cb53..5f81fcc 100644
--- a/cores/signal/nco_q15/tb/tb_nco_q15.v
+++ b/cores/signal/nco_q15/tb/tb_nco_q15.v
@@ -15,12 +15,12 @@ module tb_nco_q15();
     wire out_en;
 
     nco_q15 #(.CLK_HZ(120_000_000), .FS_HZ(40_000)) nco (
-        .clk    (clk),
-        .rst_n  (resetn),
-        .freq_hz(freq),
-        .sin_q15(sin_q15),
-        .cos_q15(cos_q15),
-        .clk_en (out_en)
+        .i_clk    (clk),
+        .i_rst_n  (resetn),
+        .i_freq_hz(freq),
+        .o_sin_q15(sin_q15),
+        .o_cos_q15(cos_q15),
+        .o_clk_en (out_en)
     );
 
     initial begin
@@ -39,4 +39,4 @@ module tb_nco_q15();
         $finish;
     end;
 
-endmodule
\ No newline at end of file
+endmodule
diff --git a/cores/signal/sd_adc_q15/rtl/rc_alpha_q15.vh b/cores/signal/sd_adc_q15/rtl/rc_alpha_q15.vh
new file mode 100644
index 0000000..27e6804
--- /dev/null
+++ b/cores/signal/sd_adc_q15/rtl/rc_alpha_q15.vh
@@ -0,0 +1,91 @@
+// rc_alpha_q15.vh
+// Plain Verilog-2001 constant function: R(ohm), C(pF), Fs(Hz) -> alpha_q15 (Q1.15)
+// Uses fixed-point approximation: 1 - exp(-x) ≈ x - x^2/2 + x^3/6, where x = 1/(Fs*R*C)
+// All integer math; suitable for elaboration-time constant folding (e.g., XST).
+
+`ifndef RC_ALPHA_Q15_VH
+`define RC_ALPHA_Q15_VH
+
+function integer alpha_q15_from_rc;
+    input integer R_OHM; // ohms
+    input integer C_PF;  // picofarads
+    input integer FS_HZ; // Hz
+
+    // Choose QN for x. N=24 is a good balance for accuracy/width.
+    integer N;
+
+    // We'll keep everything as unsigned vectors; inputs copied into vectors first.
+    reg [63:0] R_u, C_u, FS_u;
+
+    // x = 1 / (Fs * R * C) with C in pF -> x = 1e12 / (Fs*R*C_pf)
+    // x_qN = round( x * 2^N ) = round( (1e12 << N) / denom )
+    reg  [127:0] NUM_1E12_SLLN;  // big enough for 1e12 << N
+    reg  [127:0] DENOM;          // Fs*R*C
+    reg  [127:0] X_qN;           // x in QN
+
+    // Powers
+    reg  [255:0] X2;             // x^2 in Q(2N)
+    reg  [383:0] X3;             // x^3 in Q(3N)
+
+    integer term1_q15;
+    integer term2_q15;
+    integer term3_q15;
+    integer acc;
+
+begin
+    N = 24;
+
+    // Copy integer inputs into 64-bit vectors (no bit-slicing of integers)
+    R_u  = R_OHM[31:0];
+    C_u  = C_PF[31:0];
+    FS_u = FS_HZ[31:0];
+
+    // Denominator = Fs * R * C_pf  (fits in < 2^64 for typical values)
+    DENOM = 128'd0;
+    DENOM = FS_u;
+    DENOM = DENOM * R_u;
+    DENOM = DENOM * C_u;
+
+    // // Guard: avoid divide by zero
+    // if (DENOM == 0) begin
+    //     alpha_q15_from_rc = 0;
+    //     disable alpha_q15_from_rc;
+    // end
+
+    // Numerator = (1e12 << N). 1e12 * 2^24 ≈ 1.6777e19 (fits in 2^64..2^65),
+    // so use 128 bits to be safe.
+    NUM_1E12_SLLN = 128'd1000000000000 << N;
+
+    // x_qN = rounded division
+    X_qN = (NUM_1E12_SLLN + (DENOM >> 1)) / DENOM;
+
+    // Powers
+    X2 = X_qN * X_qN;
+    X3 = X2 * X_qN;
+
+    // Convert terms to Q1.15:
+    // term1 = x            -> shift from QN to Q15
+    term1_q15 = (X_qN >> (N - 15)) & 16'hFFFF;
+
+    // term2 = x^2 / 2      -> Q(2N) to Q15 and /2
+    term2_q15 = (X2 >> (2*N - 15 + 1)) & 16'hFFFF;
+
+    // term3 = x^3 / 6      -> Q(3N) to Q15, then /6 with rounding
+    begin : gen_t3
+        reg [383:0] tmp_q15_wide;
+        reg [383:0] tmp_div6;
+        tmp_q15_wide = (X3 >> (3*N - 15));
+        tmp_div6     = (tmp_q15_wide + 6'd3) / 6;
+        term3_q15    = tmp_div6[15:0];
+    end
+
+    // Combine and clamp
+    acc = term1_q15 - term2_q15 + term3_q15;
+    if (acc < 0)            acc = 0;
+    else if (acc > 16'h7FFF) acc = 16'h7FFF;
+
+    alpha_q15_from_rc = acc;
+end
+endfunction
+
+`endif
diff --git a/cores/signal/sd_adc_q15/rtl/rcmodel_q15.v b/cores/signal/sd_adc_q15/rtl/rcmodel_q15.v
new file mode 100644
index 0000000..505d4f5
--- /dev/null
+++ b/cores/signal/sd_adc_q15/rtl/rcmodel_q15.v
@@ -0,0 +1,55 @@
+`timescale 1ns/1ps
+
+// =============================================================================
+// RC model to convert sigma delta samples to Q1.15
+// Models the RC circuit on the outside of the FPGA
+// Uses: Yn+1 = Yn + (sd - Yn)*(1-exp(-T/RC))
+// parameters:
+//      -- alpha_q15 : the 1-exp(-T/RC), defaults to R=3k3, C=220p and T=1/15MHz
+//							  rounded to only use two bits (0b3b -> 0b00), the less
+//							  bits the better
+// inout:
+//      -- i_clk : input clock
+//      -- i_rst_n : reset signal
+//      -- i_sd_sample : 1 bit sample output from sd sampler
+//      -- o_sample_q15 : output samples in q.15
+// =============================================================================
+module rcmodel_q15 #(
+    parameter integer alpha_q15 = 16'sh0b00
+)(
+    input wire i_clk,
+    input wire i_rst_n,
+    input wire i_sd_sample,
+    output wire [15:0] o_sample_q15
+);
+    reg signed [15:0] y_q15;
+    wire signed [15:0] sd_q15 = i_sd_sample ? 16'sh7fff : 16'sh0000;
+    wire signed [15:0] e_q15 = sd_q15 - y_q15;
+    // wire signed [31:0] prod_q30 = $signed(e_q15) * $signed(alpha_q15);
+    wire signed [31:0] prod_q30;
+    // Use shift-add algorithm for multiplication
+    mul_const_shiftadd #(
+        .C($signed(alpha_q15)),
+        .IN_W(16),
+        .OUT_W(32)
+    ) alpha_times_e (
+        .i_x(e_q15),
+        .o_y(prod_q30)
+    );
+    wire signed [15:0] y_next_q15 = y_q15 + (prod_q30>>>15);
+
+    // clamp to [0, 0x7FFF] (keeps signal view tidy)
+    function signed [15:0] clamp01_q15(input signed [15:0] v);
+        if (v < 16'sd0000) clamp01_q15 = 16'sd0000;
+        else if (v > 16'sh7FFF) clamp01_q15 = 16'sh7FFF;
+        else clamp01_q15 = v;
+    endfunction
+
+    always @(posedge i_clk or negedge i_rst_n) begin
+        if (!i_rst_n) y_q15 <= 16'sd0000;
+        else y_q15 <= clamp01_q15(y_next_q15);
+    end
+
+    assign o_sample_q15 = y_q15;
+
+endmodule
diff --git a/cores/signal/sd_adc_q15/rtl/sd_adc_q15.v b/cores/signal/sd_adc_q15/rtl/sd_adc_q15.v
new file mode 100644
index 0000000..7130a25
--- /dev/null
+++ b/cores/signal/sd_adc_q15/rtl/sd_adc_q15.v
@@ -0,0 +1,57 @@
+module sd_adc_q15 #(
+    parameter integer R_OHM = 3300,
+    parameter integer C_PF = 220
+)(
+    input wire i_clk_15,
+    input wire i_rst_n,
+    
+    input wire i_adc_a,
+    input wire i_adc_b,
+    output wire o_adc,
+
+    output wire signed [15:0] o_signal_q15,
+    output wire o_signal_valid
+);
+    `include "rc_alpha_q15.vh"
+
+    wire sd_signal;
+    wire signed [15:0] raw_sample_biased;
+    wire signed [15:0] raw_sample_q15;
+    wire signed [15:0] lpf_sample_q15;
+
+    sd_sampler sd_sampler(
+        .i_clk(i_clk_15),
+        .i_a(i_adc_a), .i_b(i_adc_b),
+        .o_sample(sd_signal)
+    );
+    assign o_adc = sd_signal;
+
+    localparam integer alpha_q15_int = alpha_q15_from_rc(R_OHM, C_PF, 15000000);
+    localparam signed [15:0] alpha_q15 = alpha_q15_int[15:0];
+    localparam signed [15:0] alpha_q15_top = alpha_q15 & 16'hff00;
+    rcmodel_q15 #(
+        .alpha_q15(alpha_q15_top)
+    ) rc_model (
+        .i_clk(i_clk_15), .i_rst_n(i_rst_n),
+        .i_sd_sample(sd_signal),
+        .o_sample_q15(raw_sample_q15)
+    );
+
+    lpf_iir_q15_k #(
+        .K(10)
+    ) lpf (
+        .i_clk(i_clk_15), .i_rst_n(i_rst_n),
+        .i_x_q15(raw_sample_q15),
+        .o_y_q15(lpf_sample_q15)
+    );
+
+    decimate_by_r_q15 #(
+        .R(375), // 15MHz/375 = 40KHz
+        .CNT_W(10)
+    ) decimate (
+        .i_clk(i_clk_15), .i_rst_n(i_rst_n),
+        .i_valid(1'b1), .i_q15(lpf_sample_q15),
+        .o_valid(o_signal_valid), .o_q15(o_signal_q15)
+    );
+
+endmodule
diff --git a/cores/signal/sd_adc_q15/rtl/sd_sampler.v b/cores/signal/sd_adc_q15/rtl/sd_sampler.v
new file mode 100644
index 0000000..e17fa19
--- /dev/null
+++ b/cores/signal/sd_adc_q15/rtl/sd_sampler.v
@@ -0,0 +1,18 @@
+module sd_sampler(
+    input wire i_clk,
+    input wire i_a,
+    input wire i_b,
+    output wire o_sample
+);
+
+    wire comp_out;
+    lvds_comparator comp (
+        .a(i_a), .b(i_b), .o(comp_out)
+    );
+
+    reg registered_comp_out;
+    always @(posedge i_clk) 
+        registered_comp_out <= comp_out;
+    assign o_sample = registered_comp_out;
+
+endmodule
diff --git a/cores/signal/sd_adc_q15/sd_adc_q15.core b/cores/signal/sd_adc_q15/sd_adc_q15.core
new file mode 100644
index 0000000..361973d
--- /dev/null
+++ b/cores/signal/sd_adc_q15/sd_adc_q15.core
@@ -0,0 +1,57 @@
+CAPI=2:
+
+name: joppeb:signal:sd_adc_q15:1.0
+description: Sigma-delta ADC front-end with Q1.15 output
+
+filesets:
+    rtl_common:
+        depend:
+            - joppeb:primitive:lvds_comparator
+            - joppeb:signal:lpf_iir_q15_k
+            - joppeb:signal:decimate_by_r_q15
+            - joppeb:util:mul_const
+        files:
+            - rtl/rc_alpha_q15.vh:
+                is_include_file: true
+            - rtl/rcmodel_q15.v
+            - rtl/sd_adc_q15.v
+        file_type: verilogSource
+    rtl_sampler:
+        files:
+            - rtl/sd_sampler.v
+        file_type: verilogSource
+    sim_sampler:
+        files:
+            - sim/sd_sampler.v
+        file_type: verilogSource
+    tb:
+        files:
+            - tb/tb_sd_adc_q15.v
+        file_type: verilogSource
+
+targets:
+    default:
+        filesets:
+            - rtl_common
+            - rtl_sampler
+        toplevel: sd_adc_q15
+        parameters:
+            - R_OHM
+            - C_PF
+    sim:
+        default_tool: icarus
+        filesets:
+            - rtl_common
+            - sim_sampler
+            - tb
+        toplevel: tb_sd_adc_q15
+
+parameters:
+    R_OHM:
+        datatype: int
+        description: RC filter resistor value in ohms
+        paramtype: vlogparam
+    C_PF:
+        datatype: int
+        description: RC filter capacitor value in pF
+        paramtype: vlogparam
diff --git a/cores/signal/sd_adc_q15/sim/sd_sampler.v b/cores/signal/sd_adc_q15/sim/sd_sampler.v
new file mode 100644
index 0000000..99f2d1a
--- /dev/null
+++ b/cores/signal/sd_adc_q15/sim/sd_sampler.v
@@ -0,0 +1,111 @@
+`timescale 1ns/1ps
+
+// =============================================================================
+// Sigma-Delta sampler
+// Simulates an RC circuit between o_sample and i_b and i_a sine at i_a
+// =============================================================================
+module sd_sampler(
+    input wire i_clk,
+    input wire i_a,
+    input wire i_b,
+    output wire o_sample
+);
+
+    // Sine source (i_a input / P)
+    parameter real    F_HZ       = 5000;   // input sine frequency (1 kHz)
+    parameter real    AMP        = 1.5;     // sine amplitude (V)
+    parameter real    VCM        = 1.65;    // common-mode (V), centered in 0..3.3V
+
+    // Comparator behavior
+    parameter real    VTH        = 0.0;     // threshold on (vp - vn)
+    parameter real    VHYST      = 0.05;     // symmetric hysteresis half-width (V)
+    parameter integer ADD_HYST   = 0;       // 1 to enable hysteresis
+
+    // 1-bit DAC rails (feedback into RC)
+    parameter real    VLOW       = 0.0;     // DAC 0 (V)
+    parameter real    VHIGH      = 3.3;     // DAC 1 (V)
+
+    // RC filter (i_b input / N)
+    parameter real    R_OHMS     = 3300.0;  // 3.3k
+    parameter real    C_FARADS   = 220e-12; // 220 pF
+
+    // Integration step (ties to `timescale`)
+    parameter integer TSTEP_NS   = 10;      // sim step in ns (choose << tau)
+
+    // ===== Internal state (simulation only) =====
+    real vp, vn;          // comparator i_a/i_b inputs
+    real v_rc;            // RC node voltage (== vn)
+    real v_dac;           // DAC output voltage from o_sample
+    real t_s;             // time in seconds
+    real dt_s;            // step in seconds
+    real tau_s;           // R*C time constant in seconds
+    real two_pi;
+    reg  q;               // comparator latched output (pre-delay)
+    reg  out;
+    reg  sampler;
+
+    initial sampler <= 1'b0;
+    always @(posedge i_clk) begin
+        sampler <= out;
+    end
+    assign o_sample = sampler;
+
+
+    // Helper task: update comparator with optional hysteresis
+    task automatic comp_update;
+        real diff;
+    begin
+        diff = (vp - vn);
+
+        if (ADD_HYST != 0) begin
+            // simple symmetric hysteresis around VTH
+            if (q && (diff < (VTH - VHYST))) q = 1'b0;
+            else if (!q && (diff > (VTH + VHYST))) q = 1'b1;
+            // else hold
+        end else begin
+            q = (diff > VTH) ? 1'b1 : 1'b0;
+        end
+    end
+    endtask
+
+    initial begin
+        // Init constants
+        two_pi = 6.283185307179586;
+        tau_s  = R_OHMS * C_FARADS;       // ~7.26e-7 s
+        dt_s   = TSTEP_NS * 1.0e-9;
+
+        // Init states
+        t_s  = 0.0;
+        q    = 1'b0;                      // start low
+        out  = 1'b0;
+        v_dac= VLOW;
+        v_rc = (VHIGH + VLOW)/2.0;        // start mid-rail to reduce start-up transient
+        vn   = v_rc;
+        vp   = VCM;
+
+        // Main sim loop
+        forever begin
+            #(TSTEP_NS);                  // advance discrete time step
+            t_s  = t_s + dt_s;
+
+            // 1) Update DAC from previous comparator state
+            v_dac = sampler ? VHIGH : VLOW;
+
+            // 2) RC low-pass driven by DAC: Euler step
+            //    dv = (v_dac - v_rc) * dt/tau
+            v_rc  = v_rc + (v_dac - v_rc) * (dt_s / tau_s);
+            vn    = v_rc;
+
+            // 3) Input sine on i_a
+            vp    = VCM + AMP * $sin(two_pi * F_HZ * t_s);
+
+            // 4) Comparator decision (with optional hysteresis)
+            comp_update();
+
+            // 5) Output with propagation delay
+            out = q;
+        end
+    end
+
+
+endmodule
diff --git a/cores/signal/sd_adc_q15/tb/tb_sd_adc_q15.v b/cores/signal/sd_adc_q15/tb/tb_sd_adc_q15.v
new file mode 100644
index 0000000..c5ce51f
--- /dev/null
+++ b/cores/signal/sd_adc_q15/tb/tb_sd_adc_q15.v
@@ -0,0 +1,36 @@
+`timescale 1ns/1ps
+
+module tb_sd_adc_q15();
+    // Clock and reset generation
+    reg clk;
+    reg resetn;
+    initial clk <= 1'b0;
+    initial resetn <= 1'b0;
+    always #6.667 clk <= !clk;
+    initial #40 resetn <= 1'b1;
+
+    // Default run
+    initial begin
+        $dumpfile("out.vcd");
+        $dumpvars;
+        #2_000_000
+        $finish;
+    end;
+
+    wire sd_a;
+    wire sd_b;
+    wire sd_o;
+    wire signed [15:0] decimated_q15;
+    wire decimated_valid;
+
+    sd_adc_q15 #(
+        .R_OHM(3300),
+        .C_PF(220)
+    ) dut(
+        .i_clk_15(clk), .i_rst_n(resetn),
+        .i_adc_a(sd_a), .i_adc_b(sd_b), .o_adc(sd_o),
+        .o_signal_q15(decimated_q15),
+        .o_signal_valid(decimated_valid)
+    );
+
+endmodule
diff --git a/cores/system/test/rtl/toplevel.v b/cores/system/test/rtl/toplevel.v
index e14c9f8..49830a5 100644
--- a/cores/system/test/rtl/toplevel.v
+++ b/cores/system/test/rtl/toplevel.v
@@ -81,12 +81,12 @@ module toplevel #(
         .CLK_HZ(15_000_000),
         .FS_HZ(80_000)
     ) nco (
-        .clk    (clk_15),
-        .rst_n  (sys_resetn),
-        .freq_hz(GPIO_A),
-        .sin_q15(sin_q15),
-        .cos_q15(),
-        .clk_en (clk_en)
+        .i_clk    (clk_15),
+        .i_rst_n  (sys_resetn),
+        .i_freq_hz(GPIO_A),
+        .o_sin_q15(sin_q15),
+        .o_cos_q15(),
+        .o_clk_en (clk_en)
     );
 
     reg [5:0] dac_code;
diff --git a/cores/util/mul_const/mul_const.core b/cores/util/mul_const/mul_const.core
new file mode 100644
index 0000000..4602beb
--- /dev/null
+++ b/cores/util/mul_const/mul_const.core
@@ -0,0 +1,15 @@
+CAPI=2:
+
+name: joppeb:util:mul_const:1.0
+description: Constant multiplier helpers implemented with shift-add logic
+
+filesets:
+    rtl:
+        files:
+            - rtl/mul_const.v
+        file_type: verilogSource
+
+targets:
+    default:
+        filesets:
+            - rtl
diff --git a/cores/util/mul_const/rtl/mul_const.v b/cores/util/mul_const/rtl/mul_const.v
new file mode 100644
index 0000000..481e9b0
--- /dev/null
+++ b/cores/util/mul_const/rtl/mul_const.v
@@ -0,0 +1,31 @@
+`timescale 1ns/1ps
+
+module mul_const_shiftadd #(
+    parameter integer C = 0,
+    parameter integer IN_W = 16,
+    parameter integer OUT_W = 32
+)(
+    input  wire signed [IN_W-1:0] i_x,
+    output reg  signed [OUT_W-1:0] o_y
+);
+    integer k;
+    integer abs_c;
+    reg signed [OUT_W-1:0] acc;
+    reg signed [OUT_W-1:0] x_ext;
+
+    always @* begin
+        abs_c = (C < 0) ? -C : C;
+        acc = {OUT_W{1'b0}};
+        x_ext = {{(OUT_W-IN_W){i_x[IN_W-1]}}, i_x};
+
+        for (k = 0; k < 32; k = k + 1) begin
+            if (abs_c[k])
+                acc = acc + (x_ext <<< k);
+        end
+
+        if (C < 0)
+            o_y = -acc;
+        else
+            o_y = acc;
+    end
+endmodule