原标题：Microchip dsPIC33FJ128GP脉搏血氧仪设计方案

　　microchip公司的dsPIC33FJ128GP是集成了高达128KB闪存和16KB SRAM以及先进模拟特性的16位数字信号处理器(DSC),内核性能高达40MIPS,主要用在高效率马达驱动,铂级数字电源和低功耗长寿命手持设备.本文介绍了dsPIC33FJ128GP主要特性,框图,已及采用dsPIC DSC的脉搏血氧仪设计方案主要亮点,系统框图和电路图.

　　Microchip’s 16-bitdsPIC® Digital Signal Controllers provide designers with an easy upgrade path from 8-bitPIC® microcontrollers and a cost effective option to 32-bit MCUs. The broad product line includes everything from eXtreme Low Power microcontrollers to high performance digital signal controllers. With single cycle execution, deterministic interrupt response, zero overhead looping, and fast DMA, the dsPIC family also adds a single cycle 16x16 MAC and 40-bit accumulators, ideal for math intensive applications like motor control and digital power.

　　Combined with hardware and free software, these 16-bit products are ideal for designs including high efficiency Motor Control, platinum-rated Digital Power Supplies, and Low Power for longer battery life in portable applications. Integrated touch and display features help lower costs and simplify designs for user interfaces including mTouch™ Sensing, Graphics, and Segmented Display drivers. Also specialized peripherals and software for Connectivity such as USB, CAN and wireless protocols make it easy to communicate with other systems.

　　dsPIC33FJ128GP主要特性:

　　Operating Conditions

　　• 3.0V to 3.6V, -40℃ to +150℃, DC to 20 MIPS

　　• 3.0V to 3.6V, -40℃ to +125℃, DC to 40 MIPS

　　Clock Management

　　• 2% internal oscillator

　　• Programmable PLL and oscillator clock sources

　　• Fail-Safe Clock Monitor (FSCM)

　　• Independent Watchdog Timer

　　• Low-power management modes

　　• Fast wake-up and start-up

　　Core Performance

　　• Up to 40 MIPS 16-bit dsPIC33F CPU

　　• Single-cycle MUL plus hardware divide

　　Advanced Analog Features

　　• 10/12-bit ADC with 1.1Msps/500 ksps rate:

　　- Up to 13 ADC input channels and four S&H

　　- Flexible/Independent trigger sources

　　• 150 ns Comparators:

　　- Up to two Analog Comparator modules

　　- 4-bit DAC with two ranges for Analog Comparators

　　Input/Output

　　• Software remappable pin functions

　　• 5V-tolerant pins

　　• Selectable open drain and internal pull-ups

　　• Up to 5 mA overvoltage clamp current/pin

　　• Multiple external interrupts

　　System Peripherals

　　• 16-bit dual channel 100 ksps Audio DAC

　　• Cyclic Redundancy Check (CRC) module

　　• Up to five 16-bit and up to two 32-bit Timers/Counters

　　• Up to four Input Capture (IC) modules

　　• Up to four Output Compare (OC) modules

　　• Real-Time Clock and Calendar (RTCC) module

　　Communication Interfaces

　　• Parallel Master Port (PMP)

　　• Two UART modules (10 Mbps)

　　- Supports LIN 2.0 protocols

　　- RS-232, RS-485, and IrDA® support

　　• Two 4-wire SPI modules (15 Mbps)

　　• Enhanced CAN (ECAN) module (1 Mbaud) with2.0B support

　　• I2C module (100K, 400K and 1Mbaud) withSMbus support

　　• Data Converter Interface (DCI) module with I2Scodec support

　　Direct Memory Access (DMA)

　　• 8-channel DMA with no CPU stalls or overhead

　　• UART, SPI, ADC, ECAN, IC, OC, INT0

　　Qualification and Class B Support

　　• AEC-Q100 REVG (Grade 0 -40ºC to +150℃)

　　• Class B Safety Library, IEC 60730, VDE certified

　　Debugger Development Support

　　• In-circuit and in-application programming

　　• Two program breakpoints

　　• Trace and run-time watch

　　图1.dsPIC33FJ32GP302/304, dsPIC33FJ64GPX02/X04, AND dsPIC33FJ128GPX02/

　　X04框图

　　采用dsPIC DSC的脉搏血氧仪设计方案

　　Pulse Oximeter Design Using Microchip’s Analog Devices and dsPIC® Digital Signal Controllers (DSCs)

　　A pulse oximeter is a non-invasive electro-optical device for measuring both the heart rate and the degree to which the hemoglobin in one’s blood has been saturated with oxygen. This quantity is inferred by measuring the optical transmittance of perfused skin in different wavelengths of light. Red, green and infrared LEDs are convenient and common light sources. Blood oxygen saturation can be determined by comparing the values of Oxy-hemoglobin to Deoxy-hemoglobin. One method for doing this is by shining both a red LED and an infrared LED into a body part (such as a finger or wrist), and then measuring and comparing the relative intensities of the light from each LED in terms of a ratio. This ratio is then typically expressed as the percentage of oxygen saturation.

　　Pulse oximeter designs call for low power consumption and extensive analog and digital filtering. They are often implemented both as stand-alone medical and fitness devices as well as components of more comprehensive vital sign monitoring systems.

　　The ability to measure heart rate and blood oxygen level is now being added to consumer products. These measurements can be taken using pulse oximeters that are intended for home medical use and by integrated wrist-worn fitness activity trackers.

　　A pulse oximeter is a device that uses a non-invasive method for measuring the oxygen saturation level of a person’s blood, as well as their heart rate. LEDs in Microchip’s pulse oximeter demonstration transmit two wavelengths of light through a finger to a photo detector. From this, the pulse oximeter demonstration can measure changing absorbance at each of the two wavelengths, process and then filter the data to determine the blood oxygen saturation level and heart rate.

　　图2.脉搏血氧仪设计板外形图

　　The Microchip Pulse Oximeter Demonstration Board was implemented using the dsPIC33FJ128GP802 Digital Signal Controller (DSC). The features of this DSC are:

　　Up to 40 MIPS operation

　　High-Performance DSC

　　Digital FIR filter implemented in firmware

　　16 x 16 fractional/integer multiply operations

　　32/16 and 16/16 divide operations

　　Single-cycle multiply and accumulate

　　Power Management

　　On-chip 2.5V voltage regulator

　　Switch between clock sources in real time

　　Idle, Sleep, and Doze modes with fast wake-up

　　12-bit, 500 ksps/10-bit 1.1 Msps ADC module: up to 13 channels with auto-scanning

　　16-bit 100 ksps audio DAC module

　　4/4, 16-bit capture/compare/Pulse-Width Modulation (PWM) peripherals

　　Two analog comparators with programmable input/output configuration

　　Hardware RTCC: provides clock, calendar and alarm functions

　　Ten capacitive touch channels

　　This reference design helps to develop a low-cost handheld or wearable pulse oximeter with user interface.*

　　图3.脉搏血氧仪设计板框图

　　图4.脉搏血氧仪系统框图

　　脉搏血氧仪设计板亮点:

　　Measures heart rate

　　Measures percent blood oxygen saturation level

　　dsPIC33FJ128GP802 uses a 513th-order, digital-FIR, bandpass filter designed with Microchip’s free Digital Filter Design Tool

　　Integrated PWM module drives the LCD display

　　MCP1640 boost regulator, MCP4728 DAC and the MCP6002 dual op amp for reliable and accurate power management and signal conditioning

　　Low overall BOM cost due to processing and filter integration