974 Jitter Metrics & Pulse Analyzer :: Quicker, easier and cheaper to make your own chip!

974 : Jitter Metrics & Pulse Analyzer

Author: Gustavo Ismael Chavez Mamani

Description: High-speed Jitter measurement tool with UART interface and hardware gating

Clock: 50000000 Hz

How it works

This project is a high-precision Digital Jitter Meter designed to characterize signal integrity in high-speed digital systems (up to 50 MHz). It operates by measuring the temporal displacement (jitter) of a target signal (sig_in) relative to a reference clock (ref_clk).

The core architecture consists of:

High-Speed Capture Engine: Uses a 17-bit synchronous counter running at 50 MHz to sample the time difference between the reference clock and the signal transitions.
Arithmetic Unit: Calculates the absolute error ($|t_{measured} - t_{ideal}|$) and compares it against a user-configurable tolerance window.
Register Bank: Stores real-time statistics, including Maximum Jitter, Minimum Jitter, Total Samples, and an Error Counter (for picos exceeding tolerance).
Protocol FSM: A robust Finite State Machine that handles a custom UART protocol for real-time configuration and data reporting.
Hardware Gating: A physical gate_pin allows the user to pause/resume measurements instantly, ensuring data is only captured during valid test windows.

How to test

To use the Jitter Meter, follow these steps:

Setup the Clock: Provide a stable 50 MHz clock to the clk pin.
Configuration (UART): Connect a UART interface (115200 baud) to rx_pin and tx_pin.
Set Parameters:
- Send $ + I + [2 bytes] to set the Ideal Period (in clock cycles).
- Send $ + T + [2 bytes] to set the Tolerance Window.
Enable Capture: Set gate_pin to High (1) to begin analysis.
Input Signals: Apply the signal to be measured on sig_in. For best results at high frequencies, provide the source clock on ref_clk.
Retrieve Data:
- Send $ + M to get the Maximum Jitter.
- Send $ + N to get the Minimum Jitter.
- Send $ + G to get the Error Counter.
- Send $ + R to reset the statistical registers.

External hardware

Microcontroller (MCU): (e.g., ESP32, STM32, or Arduino) to send UART commands and generate the test signals.
USB-to-UART Adapter: To monitor results on a PC serial terminal.
Logic Analyzer/Oscilloscope (Optional): To verify the sig_in jitter against the reported values.
Signal Generator: To inject controlled jitter into the sig_in pin for calibration.

Input

Output

Bidirectional

rx_pin

tx_pin

sig_in

gate_pin

ref_clk

Chip location

974 Jitter Metrics & Pulse Analyzer