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capture_block/TBm_capture.slx
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capture_block/TBm_capture.slx
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@@ -1,4 +1,4 @@
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# 📡 PL Tx Subsystem (Pulse Generator)
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# 📡 PL Tx Subsystem (Pulse & Continuous LFM Generator)
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[🏠 Project Home](../README.md)
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@@ -6,7 +6,7 @@
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## Overview
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The Tx subsystem implements a **pulse-based Linear Frequency Modulated (LFM) chirp generator** using a DDS/NCO architecture in the FPGA (PL).
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The Tx subsystem implements a **pulse-based and continuous Linear Frequency Modulated (LFM) chirp generator** using a DDS/NCO architecture in the FPGA (PL).
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The generator produces **complex baseband output**:
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@@ -24,7 +24,7 @@ pulse_gen_ctrl (FSM)
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↓
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tx_active
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↓
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Phase Increment Counter
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Phase Increment Logic
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↓
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NCO (DDS)
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↓
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@@ -32,6 +32,39 @@ Phase Increment Counter
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---
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## Operating Modes
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The subsystem now supports multiple Tx modes:
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### 1. Pulsed LFM (default)
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- Chirp generated only during pulse window
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- Phase resets at each pulse start
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- Standard radar burst operation
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---
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### 2. CW Mode (Continuous Wave)
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- `tx_active = 1` continuously
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- Generates a single-tone output
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- Achieved by setting constant phase increment
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---
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### 3. Continuous LFM (Workaround Implementation)
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- `tx_active` forced HIGH continuously
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- A **1-cycle LOW pulse** is inserted periodically
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- This LOW→HIGH transition **resets the NCO**
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Result:
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- Continuous chirp
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- Bounded bandwidth
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- Periodic repetition of LFM
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---
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## Chirp Generation Principle
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The chirp is generated using a second-order phase accumulator:
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@@ -72,7 +105,7 @@ States:
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## Timing Behavior
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Within each PRI:
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### Pulsed Mode
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|<------ PRI ------>|
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|<-- pulse -->| idle |
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@@ -80,7 +113,31 @@ Within each PRI:
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- tx_active = 1 → chirp output
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- tx_active = 0 → output zero
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Chirp is reset at each pulse start.
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---
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### Continuous LFM Mode
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tx_active behavior:
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1 1 1 1 1 0 1 1 1 1 ...
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- 1-cycle LOW inserted at end of chirp period
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- Rising edge resets NCO
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- Defines chirp repetition interval
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---
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## CW / Continuous LFM Implementation Details
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- CW mode bypasses FSM output
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- A dedicated counter generates periodic reset pulses
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- Reset timing is based on `pulse_width_cycles`
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Important:
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- Reset pulse is exactly **1 clock cycle**
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- Ensures deterministic NCO restart
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- Decoupled from PRI/FSM timing
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---
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@@ -97,7 +154,19 @@ Chirp is reset at each pulse start.
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- Deterministic timing (128 MHz)
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- Efficient DDS (adder-based)
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- Complex output (I/Q)
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- Supports burst-mode radar operation
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- Supports:
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- Pulsed radar mode
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- Continuous wave (CW)
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- Continuous LFM (periodic chirp)
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---
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## Design Notes
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- FSM controls **timing (when to transmit)**
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- NCO controls **frequency evolution**
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- Continuous LFM implemented via **tx_active edge reuse**
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- Minimal hardware overhead (no additional NCO logic)
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---
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info/>
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info location="1" type="DIR_SIGNIFIER"/>
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@@ -0,0 +1,6 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info>
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<Category UUID="FileClassCategory">
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<Label UUID="design"/>
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</Category>
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</Info>
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info location="TBm_capture.slx" type="File"/>
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info Ref="capture_block" Type="Relative"/>
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info location="14d75155-da33-4258-97c9-15567dccec3d" type="Reference"/>
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info/>
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@@ -0,0 +1,2 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<Info location="capture_block" type="File"/>
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Binary file not shown.
@@ -24,31 +24,34 @@ NCOCountIncDT = numerictype(1,NCOAccumWL*2,NCOAccumWL);
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%% Test signal parameters
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% Pulse width
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pulseWidth = 8.5e-6;
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pulseWidth = 4e-6;
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% Pulse start/end frequencies
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pulseCentFreq = 125e6;
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pulseBw = 50e6; % Pulse bandwidth
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pulseCentFreq = 100e6;
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pulseBw = 5e6; % Pulse bandwidth
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% Number of pulses
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numPulses = 4;
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numPulses = 10;
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% Pulse repetition interval
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PRF = 20e3;
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PRI = 1/PRF;
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% CW mode (bypass pulse generation)
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CwMode = true;
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% Output gain
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pulseGenGain = 1;
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%% Software parameters
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% Signal generator update rate
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TsSW = 0.0025;
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TsSW = 0.5e-3;
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%% Simulation parameters
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% Sim run time
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stoptime = 10*TsSW;
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stoptime = 10*TsSW; %TsFPGA*(1*128+348)
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%% Channelizer parameters
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@@ -76,32 +79,3 @@ nFrames = nChan/SamplesPerCycle;
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% Frame size after serializing x2
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%frameSize = SamplesPerCycle/2;
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% function soc_rfsoc_init(mdlPath)
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% % Initialization fcn for the model. It sets the model-wide params
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% % which are derived based on sample rate.
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%
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% % 'FrameSize and 'NumBuffers' variables are set during model
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% % PreLoadFcn callback into base workspace. These two variables should be
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% % changed directly at the MATLAB command
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%
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% % FrameSize = evalin('base','FrameSize');
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%
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% dacSampleRate = get_param([mdlPath '/RF Data Converter'], 'dacSampleRate');
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% dacSampleRate = evalin('base', dacSampleRate)*1e6;
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% dacSamplesPerCycle = str2double(get_param([mdlPath '/RF Data Converter'], 'dacSamplesPerCycle'));
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% dacInterpolationMode = str2double(get_param([mdlPath '/RF Data Converter'], 'interpolationMode'));
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% streamClkFrequency = dacSampleRate/(dacSamplesPerCycle*dacInterpolationMode);
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%
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% SampleTime = 1/streamClkFrequency;
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%
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% % derived model-wide variables set into base workspace.
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% assignin('base','FPGAClkRate', streamClkFrequency);
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% assignin('base','TsFPGA', SampleTime);
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% assignin('base','SamplesPerCycle', dacSamplesPerCycle);
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% assignin('base','IntDecFactor', dacInterpolationMode);
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% end
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