detailed subsystems

docs/pl_tx_subsystem.md

@@ -1,50 +1,108 @@
 # 📡 PL Tx Subsystem (Pulse Generator)
 
+[🏠 Project Home](../README.md)
+
+---
+
 ## Overview
 
-The Tx subsystem implements a pulse-based LFM chirp generator using a DDS/NCO architecture.
+The Tx subsystem implements a **pulse-based Linear Frequency Modulated (LFM) chirp generator** using a DDS/NCO architecture in the FPGA (PL).
+
+The generator produces **complex baseband output**:
+
+x[n] = exp(j·φ[n])
+
+and operates deterministically in the PL after a trigger from the PS.
 
 ---
 
 ## Architecture
 
-TxPulseStart → pulse_gen_ctrl → tx_active → NCO → Output
+TxPulseStart (PS)
+        ↓
+pulse_gen_ctrl (FSM)
+        ↓
+   tx_active
+        ↓
+Phase Increment Counter
+        ↓
+      NCO (DDS)
+        ↓
+   Complex Output (I/Q)
 
 ---
 
-## Chirp Generation
+## Chirp Generation Principle
+
+The chirp is generated using a second-order phase accumulator:
 
 Δφ[n] = Δφ[n−1] + step  
 φ[n]  = φ[n−1] + Δφ[n]
 
+This results in a linear frequency sweep.
+
 ---
 
-## Parameterization
+## Parameterization (PS → PL)
 
-- Fc (center frequency)
-- B (bandwidth)
+Inputs:
+
+- Center frequency: Fc  
+- Bandwidth: B  
+- Pulse width: N (samples)
+
+Derived internally:
 
-Derived:
 f_start = Fc − B/2  
 step    = B / (N − 1)
 
+These values are converted to DDS phase increments before being written to PL registers.
+
 ---
 
-## Pulse Timing
+## Pulse Timing (FSM)
+
+States:
+
+- IDLE: waits for trigger and latches parameters  
+- ACTIVE: generates pulses  
+- DONE: waits for trigger reset  
+
+---
+
+## Timing Behavior
+
+Within each PRI:
 
 |<------ PRI ------>|
 |<-- pulse -->| idle |
 
+- tx_active = 1 → chirp output  
+- tx_active = 0 → output zero  
+
+Chirp is reset at each pulse start.
+
 ---
 
-## Trigger
+## Burst Trigger (PS Interaction)
 
-Controlled via TxPulseStart (from PS subsystem)
+- Controlled via TxPulseStart (memory-mapped register)
+- Rising edge triggers burst
+- PL runs autonomously afterward
+
+---
+
+## Key Characteristics
+
+- Deterministic timing (128 MHz)
+- Efficient DDS (adder-based)
+- Complex output (I/Q)
+- Supports burst-mode radar operation
 
 ---
 
 ## 🔗 Related Components
 
-- [Project Overview (README)](../README.md)
-- [PS Subsystem](ps_subsystem.md)
+- [🏠 Project Home](../README.md)
 - [PL Rx Subsystem](pl_rx_subsystem.md)
+- [PS Subsystem](ps_subsystem.md)