脈搏血氧儀以非介入方式測量血液中的含氧量,包括發(fā)射路徑,接收路徑,顯示和背光,數(shù)據(jù)接口以及音頻報(bào)警。發(fā)射路徑包括紅光LED,紅外光LED和用于驅(qū)動(dòng)LED的DAC。接收路徑包括光電二極管傳感器,信號(hào)調(diào)理,模數(shù)轉(zhuǎn)換器和處理器。ADI的脈搏血氧儀解決方案采用ADuC7024精密模擬微控制器,具有多達(dá)16路的12位1MSPS的ADC和采用ARM7TDMI核16位/32位RISC架構(gòu)的MCU.本文介紹了ADuC7019/20/21/22/24/25/26/27/28/29主要特性和功能框圖, ADuC7024評(píng)估板主要特性, 電路圖和材料清單,以及ADI脈搏血氧儀功能框圖及其主要元件表, 脈搏血氧儀演示系統(tǒng)框圖和所用的主要產(chǎn)品表.

The ADuC7019/20/21/22/24/25/26/27/28/29 are fully integrated, 1 MSPS, 12-bit data acquisition systems incorporating high performance multichannel ADCs, 16-bit/32-bit MCUs, and Flash®/EE memory on a single chip.

The ADC consists of up to 12 single-ended inputs. An additional four inputs are available but are multiplexed with the four DAC output pins. The four DAC outputs are available only on certain models (ADuC7020, ADuC7026, ADuC7028, and ADuC7029). However, in many cases where the DAC outputs are not present, these pins can still be used as additional ADC inputs, giving a maximum of 16 ADC input channels. The ADC can operate in single-ended or differential input mode. The ADC input voltage is 0 V to VREF. A low drift band gap reference, temperature sensor, and voltage comparator complete the ADC peripheral set.

Depending on the part model, up to four buffered voltage output DACs are available on-chip. The DAC output range is programmable to one of three voltage ranges.

The devices operate from an on-chip oscillator and a PLL generating an internal high frequency clock of 41.78 MHz (UCLK). This clock is routed through a programmable clock divider from which the MCU core clock operating frequency is generated. The microcontroller core is an ARM7TDMI®, 16-bit/32-bit RISC machine, which offers up to 41 MIPS peak performance. Eight kilobytes of SRAM and 62 kilobytes of nonvolatile Flash/EE memory are provided on-chip. The ARM7TDMI core views all memory and registers as a single linear array.

On-chip factory firmware supports in-circuit serial download via the UART or I2C serial interface port; nonintrusive emulation is also supported via the JTAG interface. These features are incorporated into a low cost QuickStart™ development system supporting this MicroConverter® family.

The parts operate from 2.7 V to 3.6 V and are specified over an industrial temperature range of −40℃ to +125℃. When operating at 41.78 MHz, the power dissipation is typically 120 mW. The ADuC7019/20/21/22/24/25/26/27/28/29 are available in a variety of memory models and packages (see Ordering Guide).

ADuC7019/20/21/22/24/25/26/27/28/29主要特性:

Analog I/O

Multichannel, 12-bit, 1 MSPS ADC

Up to 16 ADC channels1

Fully differential and single-ended modes

0 V to VREF analog input range

12-bit voltage output DACs

Up to 4 DAC outputs available1

On-chip voltage reference

On-chip temperature sensor (±3°C)

Voltage comparator

Microcontroller

ARM7TDMI core, 16-bit/32-bit RISC architecture

JTAG port supports code download and debug

Clocking options

Trimmed on-chip oscillator (±3%)

External watch crystal

External clock source up to 44 MHz

41.78 MHz PLL with programmable divider

Memory

62 kB Flash/EE memory, 8 kB SRAM

In-circuit download, JTAG-based debug

Software-triggered in-circuit reprogrammability

On-chip peripherals

UART, 2× I2C® and SPI serial I/O

Up to 40-pin GPIO port1

4× general-purpose timers

Wake-up and watchdog timers (WDT)

Power supply monitor

3-phase, 16-bit PWM generator1

Programmable logic array (PLA)

External memory interface, up to 512 kB1

Power

Specified for 3 V operation

Active mode: 11 mA @ 5 MHz, 40 mA @ 41.78 MHz

Packages and temperature range

From 40-lead 6 mm × 6 mm LFCSP to 80-lead LQFP1

Fully specified for –40℃ to +125℃ operation

Tools

Low cost QuickStart™ development system

Full third-party support

ADuC7019/20/21/22/24/25/26/27/28/29應(yīng)用:

Industrial control and automation systems

Smart sensors, precision instrumentation

Base station systems, optical networking

圖1.ADuC7026方框圖

圖2.ADuC7020典型系統(tǒng)配置圖

ADuC7024評(píng)估板

Development system for evaluation of the ADuC7024/25, fully integrated, 1 MSPS, 12-bit data acquisition systems incorporating high performance multichannel ADCs, 16-bit/32-bit MCUs, and Flash/EE memory on a single chip.

ADuC7024評(píng)估板主要特性:

• 2-layer PCB (4” 5” form factor)

• 9 V power supply regulated to 3.3 V on board

• 4-pin UART header to connect to RS232 interface cable

• 20-pin standard JTAG connector to connect to ULINK emulator

• Demonstration circuit

• 32.768 kHz watch crystal to drive the PLL clock

• ADR291 2.5 V external reference chip

• Reset/Download/IRQ0 push-buttons

• Power indicator/general-purpose LEDs

• Access to all ADC inputs and DAC outputs from external header. All device ports are brought out to external header pins.

• Surface-mount and through-hole general-purpose prototype area

圖3.ADuC7024評(píng)估板電路圖
ADuC7024評(píng)估板材料清單:

ADI脈搏血氧儀解決方案

脈搏血氧儀以非介入方式測量血液中的含氧量，它以完全飽和水平的百分比來衡量，用單一數(shù)值來表示，即所謂血氧飽和百分比，常常稱之為SpO2。該測量基于血液中血紅蛋白的光吸收特性。在可見光譜和近紅外光譜內(nèi)，含氧血紅蛋白(HbO2)與脫氧血紅蛋白(Hb)具有不同的吸收曲線。Hb吸收的紅光頻率的光線較多，紅外光(IR)頻率的光線較少。HbO2則相反，吸收的紅光頻率的光線較少，紅外光(IR)頻率的光線較多。紅光和紅外光LED盡可能相互靠近，通過人體中的單一組織位置透射光線。紅光和紅外光LED采用時(shí)間復(fù)用處理來透射光線，因此不會(huì)相互干擾。環(huán)境光線經(jīng)過估算后，從紅光和紅外光信號(hào)中減去。一個(gè)能夠響應(yīng)紅光和紅外光的光電二極管接收光線，然后由一個(gè)跨導(dǎo)放大器產(chǎn)生與所接收光線強(qiáng)度成比例的電壓。光電二極管接收的紅光與紅外光的比值用于計(jì)算血液中的氧氣百分比。根據(jù)血液流動(dòng)的脈沖特性，還會(huì)在測量周期中確定并顯示脈搏率和強(qiáng)度。

脈搏血氧儀包括發(fā)射路徑、接收路徑、顯示和背光、數(shù)據(jù)接口以及音頻報(bào)警。發(fā)射路徑包括紅光LED、紅外光LED和用于驅(qū)動(dòng)LED的DAC。接收路徑包括光電二極管傳感器、信號(hào)調(diào)理、模數(shù)轉(zhuǎn)換器和處理器。

脈搏血氧儀系統(tǒng)設(shè)計(jì)考慮和主要挑戰(zhàn)

設(shè)計(jì)脈搏血氧儀系統(tǒng)時(shí)，需要解決多個(gè)難題，如低血流灌注、運(yùn)動(dòng)和皮膚濕度、雜散光干擾、碳氧血紅蛋白和高鐵血紅蛋白干擾等。

• 低血流灌注(小信號(hào)水平)。光電二極管測量需要寬動(dòng)態(tài)范圍和低噪聲增益的信號(hào)調(diào)理，以便捕捉脈搏事件。發(fā)射和接收路徑需要具有高分辨率DAC的高質(zhì)量、低噪聲LED驅(qū)動(dòng)電路和具有高分辨率ADC的高精度模擬前端電路。

• 運(yùn)動(dòng)和皮膚濕度。運(yùn)動(dòng)會(huì)引起偽像，這可以通過軟件算法來解決，或者利用ADXL345等加速度計(jì)來檢測并解決。

• 雜散光干擾。使用光電二極管來響應(yīng)紅光和紅外光，它很容易受環(huán)境光干擾。因此，用于過濾出紅光和紅外光目標(biāo)信號(hào)的算法非常重要，這意味著信號(hào)處理更加復(fù)雜。這種情況下，需要使用具有更高信號(hào)處理能力的DSP。

• 碳氧血紅蛋白和高鐵血紅蛋白。一氧化碳(CO)很容易與血紅蛋白結(jié)合，使血液變得更像紅色HbO2，導(dǎo)致測得的SpO2值虛高。血紅素基中的鐵處于異常狀態(tài)，無法攜帶氧（Fe+3而不是Fe+2），導(dǎo)致血紅蛋白減少，SpO2讀數(shù)虛低。使用更多波長可以提高精度，但這需要更高性能的數(shù)字處理DSP。處理時(shí)間至關(guān)重要。

圖4. 脈搏血氧儀解決方案外形圖

圖5.脈搏血氧儀功能框圖
脈搏血氧儀功能框圖中主要元件表:

圖6. 脈搏血氧儀演示系統(tǒng)框圖

脈搏血氧儀應(yīng)用主要產(chǎn)品表:

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