Is diode used for signal protection in remote medical equipment?

1, The core signal protection mechanism of diodes
1. ESD protection: Suppress static electricity impact
Remote medical devices, such as portable electrocardiographs and smart wristbands, are often operated through human contact and are prone to accumulating electrostatic charges. When device interfaces (such as USB and wireless charging modules) come into contact with external conductors, static electricity may generate tens of thousands of volts of transient high voltage, which can break through chip pins or sensor circuits. TVS diodes (such as SMBJ5.0CA) can clamp the voltage to a safe range within ps time through the Zener breakdown effect (such as 5V system clamping to 10V), with a dynamic resistance as low as 0.5 Ω, and can absorb several kilowatts of surge power. For example, a certain brand of insulin pump successfully passed the IEC 61000-4-2 ESD test after using TVS diode to protect the charging interface, and the device function was not affected under 30A peak current surge.

2. Signal limiting: prevent voltage overload
Remote medical equipment needs to transmit physiological signals through wireless modules (such as Bluetooth, Wi Fi), but the antenna receiving end may generate voltage spikes due to environmental interference. Ordinary diodes (such as 1N4148) can be used to construct a limiting circuit, which limits the signal voltage within a safe range. Its working principle is: when the input voltage exceeds the forward voltage drop of the diode (about 0.7V), the diode conducts, and excess energy is consumed through the voltage divider resistor to avoid damage to the subsequent circuit (such as ADC converter) due to overvoltage. For example, in blood oxygen saturation monitoring equipment, a limiting circuit can ensure that the weak signal (mV level) output by the photoelectric sensor is not affected by external interference.

3. Reverse current blocking: ensuring power supply stability
Remote medical equipment often uses lithium batteries for power supply. If the battery is reversed or the charging circuit fails, it may cause reverse current surge. Schottky diodes (such as SS14) are the preferred choice for reverse current blocking due to their low forward voltage drop (0.2-0.3V) and fast switching characteristics. For example, a certain model of intelligent surface mount defibrillator successfully limited the reverse current to below 0.1 μ A after parallel connection of SS14 diode at the battery output terminal, far below the battery safety threshold, significantly extending the device's service life.

2, Typical application scenarios and circuit design
1. ESD protection of wireless communication module
The wireless module of remote medical equipment (such as Bluetooth, 4G/5G) must meet the IEC 61000-4-5 surge immunity standard. During design, TVS diodes need to be parallel connected to antenna interfaces and data transmission lines (such as I2C, SPI). For example:

D1/D2：SMBJ5.0CA, Protect the 5V power cord;
D3/D4: SLESD5V0LED02 (low junction capacitance 0.28pF), protects data transmission lines.
This type of design ensures that the equipment can operate stably in humid and sweaty environments, meeting medical electrical safety standards such as IEC 60601-1.

2. Limiting protection of physiological signal acquisition circuit
The amplitude of the electrocardiogram (ECG) signal is only 1-5mV, which is susceptible to power frequency interference (50Hz) and muscle electrical noise. When designing, a limiting circuit should be connected in series at the signal input end, for example:

D1/D2:1N4148 diode, forming a bidirectional limiter;
R1/R2:10k Ω voltage divider resistor, limiting current;
C1: 0.1 μ F filtering capacitor to suppress high-frequency noise.
This circuit can limit the input signal within ± 0.7V range, ensuring the normal operation of the subsequent amplifier (such as INA128).

3. Reverse protection of battery management system
Wearable remote monitoring devices (such as smart bracelets) require long-term standby, and battery self discharge and circuit leakage may shorten the battery life. By connecting a low leakage current diode (such as BAS70) in series at the battery output, the standby current can be reduced from 10 μ A to below 0.1 μ A. For example, after a certain brand of continuous blood glucose monitor adopted this solution, the device's battery life was extended from 3 days to 10 days.

3, Industry Trends and Challenges
1. Application of wide bandgap materials
Gallium nitride (GaN) based diodes have begun to be applied in remote medical devices due to their high frequency and efficiency characteristics. For example, GaN Schottky diodes have a 90% shorter reverse recovery time (trr) than silicon-based devices, which can reduce energy loss in charging circuits and improve device endurance.

2. Integrated design
To reduce the size of the device, diodes are being integrated with power management units (PMUs) and BMS chips. For example, a single-chip solution launched by a certain manufacturer integrates TVS diodes, voltage regulator diodes, and MOSFETs into a 0.8mm × 0.8mm package to meet the needs of ultra small devices such as smart rings.

3. Balance low power consumption and high reliability
Remote medical equipment is sensitive to power consumption, but at the same time needs to meet high reliability requirements. Future diodes need to break through in the following directions:

Lower forward voltage drop: such as using Super Junction technology to reduce the voltage drop of Schottky diodes to below 0.1V;
Higher reverse withstand voltage: Develop micro diodes with a withstand voltage of over 100V to meet the needs of high-power devices;
Intelligent protection function: Combining sensors and algorithms to dynamically adjust diode parameters and optimize protection effects.