ã€Abstract】 This paper introduces the application of AD's new generation of high-performance isolation amplifiers and high-precision, low-noise instrument amplifiers to design a new generation of multi-channel, high-performance physiological parametric amplifiers. Physiological parameter measurement amplifier is an important unit circuit for measuring physiological parameters such as biopotential, blood pressure and body temperature. At present, most of the physiological parameter amplifiers use amplifiers for three op amps, supplemented by floating circuits of discrete devices. Although they can meet general requirements, due to low integration, many components are used, the structure is complicated, and debugging is difficult. It is difficult to meet the requirements of high stability, high common mode rejection ratio, and high safety of various current weak physiological parameter measurements. After several years of research and experiment, the author uses AD620 high-precision instrument amplifier and AD204 small isolation amplifier to form ECG, EEG, EMG, ventricular late potential, high-frequency ECG, Various weak potential measuring amplifiers such as His's beam diagram ensure perfect performance and improve the index, which makes the design debugging extremely simplified, and the number of devices can generally be reduced to 1/5 of the ordinary circuit, which satisfies the physiological signal preamplification. The isolation, low noise, low drift, high impedance, high common mode rejection ratio, and high insulation performance solve the difficult problems that have been difficult to solve for many years. The AD62O uses a laser wafer calibration process to ensure proper matching and tracking performance between circuit components, thus ensuring the inherent high performance of the circuit. Figure 1 is a simplified circuit structure and connection diagram of the AD62O. As shown in Figure 1, TI and TZ are super R structures, which are connected to a differential bipolar input mode, which enables the circuit to have high input impedance and high precision performance. AI, AZ, and A3 are similar to the three op amp structure, and all common mode signals are eliminated by A3, and the gain is G1 (RI+RZ)/Rg+1. Because of the Rg external structure, it is easy to adjust the gain of the amplifier. Since RI, RZ has been calibrated to an absolute value of 24.7K, and its gain formula is: G_(RI+RZ)/Rg+1-49.4K/Rg+1, so Rg is 49.4K/(G-I). The AD620 is available in an 8-pin DIP package that is down to three steps smaller than the three op amp circuit and consumes only 1.3mA. Due to the ultra-p processing, the input bias current is only InA, which guarantees high impedance, low noise and high common mode rejection ratio of the module. When used at low frequencies, the noise level is only O. 28pV. . The input impedance can reach IOG ohms and the common mode rejection ratio can reach 14OdB. From the safety performance of the physiological parameter measurement amplifier, the requirements of the International Electrotechnical Commission (IEC) in terms of general safety standards are quite demanding. If isolation is not used, it is difficult to achieve a patient leakage current less than O. ipA technical requirements. At present, the commonly used floating technology has electromagnetic coupling and photoelectric coupling. The frequency characteristics of photoelectric coupling are better, and the linearity is relatively poor. The linearity of electromagnetic coupling is better than that of photoelectric coupling. However, because of the need to modulate and demodulate the circuit, the transformer is also wound, and the process is complicated. Because the AD204 uses surface mount technology and integrated modular technology to overcome the above shortcomings, it provides an ideal application device for physiological parameter amplifiers with relatively low frequency response requirements. Although the optocoupler has smashed the power transformer, the front-end power supply still needs to suspend the power supply, and it is impossible to get rid of the trouble of winding the transformer. Therefore, the advantage of the isolation module and the floating power supply is more prominent. The main technical performance of AD2O4: 1 small size: four channels per inch; 2 low power consumption: typical power consumption is 35mw; 3 high accuracy: the maximum nonlinear distortion is only O. O25% (K grade); 4 high common mode rejection performance: when the gain is IO0 times, up to 130dB; 5 frequency characteristics: the passband can reach SKHZ; 6 high insulation isolation: breakdown voltage up to 2000V peak (K grade); 7 has an isolated power output. As shown in Figure 2, the AD204 uses amplitude modulation technology to achieve signal conversion coupling to achieve the purpose of floating amplification. It contains an op amp, modulator, demodulator and a power conversion system. The power converter is driven by a 25KHZ square wave with a peak value of 15V. This square wave comes from the external supporting circuit AD246. The output voltage of the entire isolator is equal to the output voltage of the op amp, that is, the isolator has unity gain. The op amp can achieve the desired amplification gain through different connections. The modulator and demodulator are driven by a 25KHZ square wave. The VISO ten and VISO are the power output of the module to provide the suspended upper stage amplifier with a maximum load of ZmA and output ground 7. SV.
Description
-Contact Resistance:≤50mΩ
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figure 1 
figure 2
-Insulation Resistance:≥100mΩ
-Dielectric Strength:1,500V,
-1min Electronic Life:10,000 cycles
-Operating temperature:T120
-Rating current/voltage:6A 250V AC
Features
â—† Micro contact gap,high speed operation,high sensitirity,Micro operatizon travel.
â—† Long life & high reliability
January 11, 2023