Application of low power op amps in portable medical and fire fighting systems

In recent years, electronic products powered by batteries have been widely used, and designers are eager to use low-voltage analog circuits to reduce power consumption. Low-voltage, low-power, and low-noise analog circuit design technology is becoming a hot topic of research. From the perspective of energy conservation, low power consumption is not only a requirement for battery-driven portable devices, but also an urgent need for large systems using AC power. It can not only extend the use time of the device, but also delay the aging of the device. Operational amplifier As the most basic unit in integrated circuits, its importance is well known. In low-voltage operational amplifiers, due to the reduction of power supply voltage, the dynamic range of the signal is reduced. At the same time, the amplitude of the noise signal is relatively increased, and the signal-to-noise ratio of the amplifier is reduced. In order to solve these design problems, Dio Microelectronics has specially developed several low-power and low-noise operational amplifiers to meet this market demand.

2. Background

With the rapid development of the medical electronic equipment industry, mobile handheld medical electronic equipment for personal health care is also developing rapidly. Whether it is a handheld defibrillator or a dynamic blood glucose monitor , designing such products is not an easy task. Selecting appropriate components to meet design specifications, reducing costs as much as possible, ensuring the power of the design solution, paying special attention to the actual size of the product, etc. are all issues that must be considered during the product design process. Similarly, with the improvement of people's security awareness, smoke detection equipment has entered thousands of households, and higher requirements have been put forward for the design of fire protection products with low power consumption (long battery life), high sensitivity and reliability.

Block diagram of a blood pressure monitor

Whether it is temperature, pulse, blood sugar reading or other biosensors , implementing a proper signal amplification and conditioning chain is the most important issue. In the analog front-end circuit, the operational amplifier is the most critical unit. In this circuit, low-noise, high-precision, low-power, and low-bias current operational amplifiers are generally selected. The first stage of the signal chain generally uses high common-mode rejection ratio, low bias current (especially for infrared tube sensors), and low-noise operational amplifiers; the second stage will use low-power, high-precision, and low-noise operational amplifiers. The next stage of the signal chain is a good delta-sigma or successive approximation analog-to-digital converter (ADC). Features such as single-cycle filter settings and on-demand conversion simplify the design requirements of the ADC, increase the conversion speed, and provide a larger source impedance. With proper layout and component selection, a clean, accurate, and meaningful signal can be input to the system microprocessor/DSP.

Smoke sensor structure diagram

The alarm composed of smoke sensors can report fire in time. In the smoke sensor, a semiconductor material that is particularly sensitive to smoke is installed, such as tin oxide, zinc oxide, etc., so they are also called gas-sensitive materials. In an environment with smoke, when the concentration of smoke reaches a certain value, the resistance value inside the gas-sensitive material will drop rapidly. Once the smoke disappears, their resistance value will return to normal. Another method of smoke detection is to use the principle that infrared light is blocked by smoke, causing the infrared receiving current to change and alarm. The photoelectric method is divided into forward scattering and backward scattering detection methods. The sensor is installed in an optical maze. When there is no smoke, the sensor cannot receive or only receives very weak light signals. After amplification by the amplifier, the logic judgment circuit does not perform alarm processing. When smoke enters the maze, the light is irradiated on the smoke particles to generate scattering, and the sensor receives a relatively strong light signal. After amplification, the logic alarm circuit sends an alarm signal. In these applications, operational amplifiers are key components, requiring ultra-low power consumption, low bias current, and low noise.

3. Application of DIO2051/2052

In order to meet the needs of these markets, Dio Microelectronics has developed a DIO2051/2052 chip to meet customer needs. DIO2052/DIO2051 has a wide common-mode input range and a wide output voltage swing, a power supply operating voltage from 2.1V to 5.5V, and a temperature operating range from -40℃ to 125℃.

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The bandwidth of DIO2052/DIO2051 is 500kHz, and the static power consumption of each channel is 16uA. Using CMOS input, very low input bias current (0.5pA) can be obtained. Under the condition of 5V power supply voltage and 5K ohm resistance load, the output range can reach 0.1~4.9V, as shown in Table 1. High CMRR and PSRR, as shown in Table 2. Low static power consumption, as shown in Table 3. At the same time, DIO2052/DIO2051 has low offset (less than 1mV), low input noise, 20nV/sqrt(Hz) at greater than ＞10kHz, as shown in Table 4.

Table 1 Input-output curves under different resistance load conditions

Table 2 PSRR and CMRR

Table 3 Static power consumption versus power supply voltage curve

Table 4 Equivalent input noise

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Application of DIO2052 from Dio Microelectronics in Blood Oximeter

DIO2052 from Dio Microelectronics plays a critical role in the application of oximeters. The first stage uses three op amps to build a fully differential mode as the signal input stage, providing a high common mode rejection ratio, a wide signal dynamic range, and most importantly, eliminating the need for expensive instrument op amps. The second stage uses two op amps as signal amplification and active filter design, with good signal-to-noise ratio and low offset. In the application of oximeters, customers have achieved a very high cost-performance ratio, improved product competitiveness and accelerated time to market.

Photoelectric smoke sensor DIO2052 application example

In the design of this Photoelectric smoke sensor , the DIO2052 used by the designer meets the design requirements very well. DIO2052 has an extremely low bias current (<1pA), which can ensure that it is much smaller than the dark current of the infrared tube, improving the reliability of the sensor; DIO2052 has an extremely low power consumption (<18uA), which allows the simple battery-powered smoke sensor to work for a long time, even if it is a networked smoke sensor, it can allow more terminals to be connected to the fire control center; DIO2052 has good common mode rejection ratio, low noise and other characteristics, which ensures good circuit performance and product reliability, and meets the design concept of fire protection products.

4. Summary

As people pay more and more attention to their health and the safety of their living environment, portable medical products and fire alarm products will inevitably develop rapidly. Low-noise, high-precision, low-power operational amplifiers will be widely adopted in terminal designs.