ECG simulation based ARM9 waveform generation system design (1)

0 introduction

With the development of the community, people are increasingly concerned about health career development in medical technology have an increasingly higher demand.

Reality in many cases cannot learn through real-life cases more doctors can only make the analog devices, ECG waveform analog waveform generation system design is one such example.

ECG simulation system using four different frequency standard ECG waveform and used for testing of square wave, sawtooth wave, triangle wave and sine wave, through-out the patient's algorithm 34 abnormal ECG waveform (including adults and children), the periodic waveform can be used to insert different delay subroutine.

Extraction of hospital patients, abnormal ECG waveform by fitting methods can simulate and convert normal Defibrillation after, according to this method the waveform design a ECG system, the system can capture, simulate arbitrary-lead ECG, and stores the result to the ECG database for research analysis. Final design of a micro-controller and waveform output and keyboard convert circuit of ECG analog waveform generator.

1 system design

ECG analog waveform systems leading to ARM9 processor unit as the core, plus high-voltage defibrillation acquisition circuits, D/A conversion modules, waveform output circuits, keyboard interface circuit and monitor signal matching as well as the design of the application, etc.

ARM microprocessor is a high-performance, low-power 32-bit MCU Department, it is widely used in embedded systems.

ARM9 represents mainstream processors ARM company, already in handheld phone, set-top boxes, digital cameras, GPS, personal digital assistants, and Internet device has a wide range of applications.

The system uses the ARM9 embedded development platforms, mainly use ARM9 rich I/O resources and quick handling.

ARM9 processor's main structure and its characteristics are as follows:

(1) 32 b fixed-point RISC processor, improved ARM/Thumb code weaving, multiplier design enhancement.

Support real-time (real-TIme) debugging.

(2) on-chip SRAM, instruction and data and instructions and data storage capacity is adjustable.

(3) chip instructions and data, high-speed buffers (cache) capacities from 4 KB to 1 MB.

(4) set protection unit (protcction unit), very suitable for embedded applications in memory to be fragmented and protection.

(5) the introduction of AMBA AHB bus interface for peripherals provide a unified address and data bus.

(6) support for external coprocessor instructions and data bus with a simple handshake signalling support.

(7) support standard basic logical unit scan test methodology, and support for BIST (built-in-self-test).

(8) support embedded tracking macros, modules, support provides real-time tracking of instructions and data.

The new generation of ARM9 processor through a brand new design with more transistors, can achieve higher than the ARM7 processor two times more processing power.

Such improvements are increasing the clock frequency and the reduction of Directive implementation cycle.

2 hardware circuit and principle

This part is mainly divided into ARM9 hardware platform, D/A conversion, waveform output circuits, signal acquisition and right foot driving circuit common negative feedback circuit.

System in the ARM9 processor unit control, D/A conversion circuit to waveform data converted to analog out output. When receiving a high voltage defibrillation signal, the processor will convert the abnormal ECG waveform acquisition become normal ECG waveform diagram.

System hardware connection diagram shown in Figure 1.

2.1 D/A conversion principle

ECG analog signal must be quantified through sampling to digital content and store it in the data store for software analysis.

This process must be achieved through AD converter. A digital signal into an analogue of D/A conversion mode:

(1) use A conversion-chip D/;

(2) adopting PWM pulse width modulation, i.e.;

(3) use f-v, frequency voltage conversion.

Through the ECG signal waveform analysis, wave cycle is approximately 1 s, therefore adopt frequency voltage transformation has sufficient precision-analog conversion, frequency conversion index also meets the demands, and that means less used hardware is generally accomplished by using the software.

This section is the core of the system, in order to achieve these electric digital system simulation quantity for testing, operation and control, you need an analog and digital signal conversion between, that is, the process often requires the digital to analog, or D/A conversion, the completed this conversion circuit to DAC (Digital to Analog Converter, DAC).

In order to ensure system stability and signal requirements, D/A conversion chips using 8-bit parallel DAC0832 chip, 12-V single supply, each DAC with separate reference inputs.

DAC0832 chip structure diagram shown in Figure 2.