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896 : CFAR Detector without Buzzer

Author: Ilamparuthi G

Description: A simplified CFAR-based signal detection system using 14-bit ADC input and 7-segment display output.

Clock: 10000000 Hz

How it works

This project implements a hardware-efficient Constant False Alarm Rate (CFAR) signal detection engine, optimized for area-constrained silicon footprints. It processes a 14-bit digital input to dynamically adapt to varying noise floors and detect valid target signals.

Input Mapping: To bypass the standard 8-pin input limit, the design concatenates standard inputs with bidirectional pins configured as inputs:

ui_in[7:0]: Lower 8 bits of the incoming signal.
uio_in[5:0]: Upper 6 bits of the incoming signal (uio_oe = 0).
These combine to form a unified 14-bit data bus ({uio_in[5:0], ui_in[7:0]}).

CFAR Architecture: Instead of a memory-heavy sliding window, this design utilizes an Infinite Impulse Response (IIR) running average to estimate the background noise threshold.

The baseline threshold continually updates: threshold = (threshold + signal) >> 1.
A target is detected if the incoming signal exceeds this adaptive threshold multiplied by a fixed internal gain factor.
The resulting binary state is routed directly to a built-in 7-segment display driver, providing immediate visual feedback alongside a dedicated high/low output flag (uo_out[7]).

How to test

Initialization:
- Provide a standard clock signal to clk.
- Assert reset (rst_n = 0) to clear the internal threshold registers.
- Release reset (rst_n = 1) to begin normal operation.
Baseline / Noise Floor Test (No Detection):
- Apply a steady, low-level signal (e.g., ui_in = 50, uio_in = 0).
- Expected Result: The threshold adapts to the noise floor. The 7-segment display shows 0 and the detection flag (uo_out[7]) remains 0.
Target Detection Test (Spike):
- Inject a sudden signal spike (e.g., ui_in = 250, uio_in = 0).
- Expected Result: The signal abruptly exceeds the calculated threshold * GAIN condition. The 7-segment display immediately updates to 1 and the detection flag (uo_out[7]) goes HIGH (1).

External hardware

14-bit Signal Source: An external Analog-to-Digital Converter (ADC) or a microcontroller (e.g., Raspberry Pi Pico on the Tiny Tapeout demo board) to generate the input vectors.
7-Segment Display: The standard Tiny Tapeout PCB display to visualize the detection state.

(Note: To maximize pin availability for the 14-bit data bus, no additional external peripherals, such as buzzers, are used).

#	Input	Output	Bidirectional
0	ADC bit 0	7-seg a	ADC bit 8
1	ADC bit 1	7-seg b	ADC bit 9
2	ADC bit 2	7-seg c	ADC bit 10
3	ADC bit 3	7-seg d	ADC bit 11
4	ADC bit 4	7-seg e	ADC bit 12
5	ADC bit 5	7-seg f	ADC bit 13
6	ADC bit 6	7-seg g	unused
7	ADC bit 7	Detection output	unused

Input

Output

Bidirectional

ADC bit 0

7-seg a

ADC bit 8

ADC bit 1

7-seg b

ADC bit 9

ADC bit 2

7-seg c

ADC bit 10

ADC bit 3

7-seg d

ADC bit 11

ADC bit 4

7-seg e

ADC bit 12

ADC bit 5

7-seg f

ADC bit 13

ADC bit 6

7-seg g

unused

ADC bit 7

Detection output

unused

Chip location

896 CFAR Detector without Buzzer