path: root/doc/pulse_width_modulator_report.md

Introduction
============

A heartbeat generator can be used in a digital system to display activity of a system.
Based on population studies, a heartrate between 60 and 100 beats per minute (bpm)
is considered as normal for a human adult.

Features
========

Normal rhythm produces four entities – a P wave, a QRS complex, a T wave, and a U wave – that each
have a fairly unique pattern. [[1]](https://en.wikipedia.org/wiki/Electrocardiography)

For simplicity the existing heartbeat modules generates the QRS complex and T wave only. 

  * Models QRS-Complex and T-Wave
  * Average time values based on 72 bpm
  * Enable input for external prescaler


General Description
===================

![Heartbeat Generator - Schematic Symbol](images/heartbeat_gen_symbol.pdf){width=40%}

| **Name**    | **Type**          | **Direction** | **Polarity** | **Description** |
|-------------|-------------------|:-------------:|:------------:|-----------------|
| clk_i       | std_ulogic        | IN            | HIGH         | clock           |
| rst_ni      | std_ulogic        | IN            | LOW          | reset           |
| en_pi       | std_ulogic        | IN            | HIGH         | enable          |
| count_o     | std_ulogic_vector | OUT           | HIGH         | count value     |
| heartbeat_o | std_ulogic        | OUT           | HIGH         | hearbeat pulse output |

: Heartbeat Generator - Description of I/O Signals


Functional Description
======================

The shape of an [electrogardiogramm](https://en.wikipedia.org/wiki/Electrocardiography) as a voltage graph over time



![Electrocardiogram](images/ECG-SinusRhythmLabel.png){width=20%}

The important QRS complex and T wave are modelled as digital pulses.

![QRS Complex and T Wave Pulses](images/qrs-complex-t-wave-pulses.pdf){width=80%}


Design Description
==================

A conceptional RTL diagram is shown below.

![Heartbeat Generator - Conceptional RTL](images/heartbeat_gen_conceptional_rtl.pdf){width=60%}

The simulation result shows two full periods based on a clock period of 1 ms

![Two Periods - Simulation Result](images/heartbeat_gen_two_periods_simwave.png){width=80%}

In more detail using cursors to display correct parameters of the QRS complex and T wave.

![QRS-Complex and T-Wave - Simulation Result](images/qrs-complex-t-wave_simwave.png){width=80%}



Device Utilization and Performance
==================================

The following table shows the utilisation of both modules heartbeat_gen and cntdnmodm.

```pure
+--------------------------------------------------------------------------------------+
; Fitter Summary                                                                       ;
+------------------------------------+-------------------------------------------------+
; Fitter Status                      ; Successful - Wed Mar 31 11:50:15 2021           ;
; Quartus II 32-bit Version          ; 13.0.1 Build 232 06/12/2013 SP 1 SJ Web Edition ;
; Revision Name                      ; de1_heartbeat_gen                               ;
; Top-level Entity Name              ; de1_heartbeat_gen                               ;
; Family                             ; Cyclone II                                      ;
; Device                             ; EP2C20F484C7                                    ;
; Timing Models                      ; Final                                           ;
; Total logic elements               ; 50 / 18,752 ( < 1 % )                           ;
;     Total combinational functions  ; 50 / 18,752 ( < 1 % )                           ;
;     Dedicated logic registers      ; 26 / 18,752 ( < 1 % )                           ;
; Total registers                    ; 26                                              ;
; Total pins                         ; 15 / 315 ( 5 % )                                ;
; Total virtual pins                 ; 0                                               ;
; Total memory bits                  ; 0 / 239,616 ( 0 % )                             ;
; Embedded Multiplier 9-bit elements ; 0 / 52 ( 0 % )                                  ;
; Total PLLs                         ; 0 / 4 ( 0 % )                                   ;
+------------------------------------+-------------------------------------------------+
```

```pure

+----------------------------------------------------------------------------------------+
; TimeQuest Timing Analyzer Summary                                                      ;
+--------------------+-------------------------------------------------------------------+
; Quartus II Version ; Version 13.0.1 Build 232 06/12/2013 Service Pack 1 SJ Web Edition ;
; Revision Name      ; de1_heartbeat_gen                                                 ;
; Device Family      ; Cyclone II                                                        ;
; Device Name        ; EP2C20F484C7                                                      ;
; Timing Models      ; Final                                                             ;
; Delay Model        ; Combined                                                          ;
; Rise/Fall Delays   ; Unavailable                                                       ;
+--------------------+-------------------------------------------------------------------+

-----------------------------------------+
; Clocks                                 ; 
+------------+------+--------+-----------+
; Clock Name ; Type ; Period ; Frequency ;
+------------+------+--------+-----------+
; CLOCK_50	 ; Base ; 20.000 ; 50.0 MHz	 ;
+------------+------+--------+-----------+


+-----------------------------------------------------------------------------+
; Multicorner Timing Analysis Summary                                         ;
+------------------+-------+-------+----------+---------+---------------------+
; Clock            ; Setup ; Hold  ; Recovery ; Removal ; Minimum Pulse Width ;
+------------------+-------+-------+----------+---------+---------------------+
; Worst-case Slack ; 3.390 ; 0.241 ; 13.381   ; 3.796   ; 8.889               ;
;  CLOCK_50        ; 3.390 ; 0.241 ; 13.381   ; 3.796   ; 8.889               ;
; Design-wide TNS  ; 0.0   ; 0.0   ; 0.0      ; 0.0     ; 0.0                 ;
;  CLOCK_50        ; 0.000 ; 0.000 ; 0.000    ; 0.000   ; 0.000               ;
+------------------+-------+-------+----------+---------+---------------------+
```

Application Note
================

The following test environment on a DE1 prototype board uses a system clock frequency of 50 MHz.
A prescaler is parameterised to generate an output signal with a period of 1 ms.

![Test Environment on DE1 Prototype Board](images/de1_heartbeat_gen_schematic.pdf){width=70%}



Appendix
========

References
----------

* [Wiki: Electrocardiography](https://en.wikipedia.org/wiki/Electrocardiography)

Project Hierarchy
-----------------

### Module Hierarchy for Verification

```pure
t_heartbeat_gen(tbench)
  heartbeat_gen(rtl)
```

### Prototype Environment

```pure
de1_heartbeat_gen(structure)
  heartbeat_gen(rtl)
  cntdnmodm(rtl)
```

VHDL Sources
------------

```vhdl
LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;

ENTITY heartbeat_gen IS
  PORT (clk_i   : IN  std_ulogic;
        rst_ni  : IN  std_ulogic;
        en_pi   : IN  std_ulogic;
        count_o : OUT std_ulogic_vector;
        heartbeat_o : OUT std_ulogic
        );
END heartbeat_gen;
```

```vhdl
LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;
USE IEEE.numeric_std.ALL;

ARCHITECTURE rtl OF heartbeat_gen IS

  CONSTANT n    : natural                := 10;
  CONSTANT zero : unsigned(n-1 DOWNTO 0) := (OTHERS => '0');

  CONSTANT heartbeat_period : unsigned(n-1 DOWNTO 0) := to_unsigned(833, n);
  CONSTANT qrs_width        : unsigned(n-1 DOWNTO 0) := to_unsigned(100, n);
  CONSTANT st_width
  CONSTANT t_width
  CONSTANT qt_width

  SIGNAL next_state, current_state : unsigned(n-1 DOWNTO 0);

  SIGNAL tc_qrs                    : std_ulogic;  -- qrs interval
  SIGNAL tc_t                      : std_ulogic;  -- T wave

BEGIN

  next_state_logic : 
                     


  state_register : 
                   

  -- output_logic
  t_wave : tc_t <= 
                   
                   
                   
  qrs_complex : tc_qrs <= 
                          

  output_value : heartbeat_o <= 


END rtl;
```

Revision History
----------------

| **Date**  | **Version**  | **Change Summary**  |
|:----------|:-------------|:--------------------|
| May 2020  | 0.1  | Initial Release  |
| April 2021  | 0.2  | Added parameterisation  |