Portable medical electronics have seen considerable growth in recent years and have been widely adopted by the industry. Many newly established companies in the market continue to launch new derivative products. What is needed is a better mass-producible design that provides lower complexity and acceptable performance levels, allowing the industry to keep the cost of the device down. When designing a medical device, some important factors for industry players to consider include selecting the correct components for specifications, power consumption, cost, size, etc., and passing FDA inspections.
A typical portable medical Electronic system consists of analog front-end components for data acquisition, amplifiers and filters for signal conditioning, analog-to-digital converters, buttons for collecting user feedback, and microcomputers for computing. Controller and various interfaces for connecting the LCD screen to the USB connection port. The traditional design method is to put all the required components on the circuit board, but this method increases the overall bill of materials, PCB complexity and design cycle.
These analog parts reduce the protection of analog IP because the solution can be easily reverse-engineered by the outside world. The design and manufacture of portable medical electronic products are regulated by the U.S. Food and Drug Administration (FDA), which means that the design and manufacture of products must accurately follow the prescribed procedures, and their performance must comply with strict records, development testing, product testing and on-site maintenance.
A typical sphygmomanometer uses a differential pressure sensor to measure the blood pressure of the wrist or arm. The output signal of this sensor is only a few microvolts (30μV to 50μV). The output blood pressure signal must be amplified with a high gain instrumentation amplifier with ideal CMRR (common mode rejection ratio). Typically ideal gain and CMRR are 150dB and 100dB, respectively. The oscillating pulse frequency of the blood pressure signal is between 0.1Hz and 11Hz, and the amplitude is hundreds of microvolts. These signal oscillations can be extracted using a bandpass filter with a gain of about 200 and a cutoff frequency of 0.3Hz to 11Hz. A 10-bit analog-to-digital converter up to 50Hz can be used to digitize the blood pressure sensor and oscillator signals.
A typical contactless digital thermometer uses a sensor with a thermopile embedded in a micromachined film on a thin film, coupled with a thermoelectric cell to measure the temperature of the thermoelectric cell, and a thermistor to measure the ambient temperature. The thermoelectric corner will generate a DC voltage, and its value is directly related to the temperature difference of the joint, and the output signal of the thermoelectric corner is only a few V. The signal output from the thermoelectric corner is amplified by these low-noise precision amplifiers, using a thermistor and an external precision reference voltage to form a voltage divider.
The voltage divider converts the resistance change of the thermistor, with reference to the temperature value, into a voltage change. Thermoelectric corner and thermistor voltage, used to calculate the thermoelectric corner and ambient temperature. The system uses a polynomial function provided by the sensor manufacturer, or a look-up table with pre-stored readings, to extrapolate the temperature from the voltage and add the ambient temperature to the thermoelectric corner temperature to calculate the final temperature.
Segment LCD driver, RTC, push buttons, EEPROM, and USB are other peripheral components required for the above applications.
In addition to microcontrollers, sensors, ADCs, LCD screen drivers/controllers, USB controllers, filters, amplifiers, etc. are all peripheral components. These parts are connected to the microcontroller through GPIO or dedicated pins. The use of these peripheral components encounters many limitations and constraints, including bill of materials, complexity of printed circuit boards, FDA requirements to inspect each component thus increasing design/development time, and reducing the protection of analog IP.
Using a system-on-chip (SoC) in a sphygmomanometer can greatly simplify the design process. One SoC integrates the high-gain instrumentation amplifiers required by the product. Using an integrated analog/digital filter, the oscillating pulse signal can be extracted. The adjustable ADC in the SoC can be used to perform data digitization, and the built-in CPU core provides the necessary processing functions to execute algorithms with longer program codes. This part also integrates a segmented LCD digital screen to Display messages; EERPROM memory for recording data; real-time frequency for recording time stamps; full-speed USB to PC interface; . Timers within the SoC can be used to calculate heart rate and handle safety functions. The SoC also supports a wide range of operating voltages and consumes less current, making it more suitable for battery-operated devices. A pulse modulator within the SoC can be used to control the motor.
The SoC integrates the necessary amplifiers and ADCs to detect changes at the microvolt level within the infrared thermometer. There is a precise reference voltage inside the SoC, which can provide a stable and accurate reference signal source for the sensor. Other functions built into the SoC include Segment LCD digital screen driver, EEPROM memory, RTC, USB interface, and touch sensing.
As mentioned above, the SoC integrates most of the peripheral components. In this way, the industry can immediately save a considerable number of parts. Using this chip also protects the analog IP because all analog parts are integrated on the chip. Fewer parts count means simpler PCBs, shorter development times and shorter time-to-market. The power consumption of various peripheral components in the chip can be managed separately through different modes, and the work of power management becomes simple and efficient. The adjustable flexibility of these chips can help reduce cost and operating time when redesigning or changing solutions. More importantly, the use of a system-on-a-chip makes the FDA inspection process simpler by reducing the use of materials. Blood glucose meters, pulse oximeters, portable ECG devices, etc., these portable medical electronic devices can all use SoC.
For example, Cypress’s PSoC 3/5 products (programmable system-on-a-chip) are tailored for a variety of portable handheld devices, such as blood pressure monitors, blood glucose meters, and pulse oximeters. PSoC3/5 combines an 8051/ARM cortex M3 core with speeds of 33MIPS and 100 DMIPS, as well as amplifiers, 2KB of EEPROM, full-speed USB 2.0, and many other features to create a true single-chip solution. Combined with the PSoC Creator IDE, it provides pre-programmed tunable IP blocks for each function, providing product designers with all the necessary tools to develop miniaturized, highly programmable end products with extremely short design cycles. The low power consumption characteristics of PSoC 3/5 components are more suitable for supporting handheld medical/life and leisure electronic products.
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