Low Cost, Low Power Instrumentation Amplifier# AD620BN Instrumentation Amplifier Technical Documentation
*Manufacturer: Analog Devices Inc. (ADI)*
## 1. Application Scenarios
### Typical Use Cases
The AD620BN is a low-cost, high-accuracy instrumentation amplifier specifically designed for precision signal conditioning applications requiring high common-mode rejection and low DC errors.
Primary Applications:
- Medical Instrumentation : ECG/EEG monitoring systems, blood pressure monitors, and patient monitoring equipment where high CMRR is critical for rejecting 50/60 Hz power line interference
- Industrial Process Control : Bridge signal conditioning for pressure transducers, load cells, and temperature sensors in harsh industrial environments
- Data Acquisition Systems : Front-end signal conditioning for multi-channel measurement systems requiring high input impedance and differential signal processing
- Test and Measurement Equipment : Precision voltage measurement instruments, strain gauge amplifiers, and low-level signal amplification
### Industry Applications
Medical Sector : The AD620BN excels in biomedical applications due to its:
- High CMRR (100 dB min at G = 10) effectively rejects common-mode interference
- Low input bias current (1 nA max) minimizes electrode polarization effects
- Low power consumption (1.3 mA max) suitable for portable medical devices
Industrial Automation :
- Process control systems utilizing 4-20 mA current loops
- Motor control feedback systems
- PLC analog input modules
- Weighing scale and force measurement systems
Automotive Systems :
- Sensor signal conditioning (pressure, position, temperature)
- Battery monitoring systems
- Diagnostic equipment interfaces
### Practical Advantages and Limitations
Advantages:
- High Accuracy : Maximum 50 μV input offset voltage and 0.3 μV/°C drift
- Flexible Gain Setting : Programmable gain from 1 to 10,000 using single external resistor
- Excellent CMRR : Minimum 100 dB at G = 10, rejecting common-mode noise
- Low Noise : 0.28 μV p-p noise (0.1 Hz to 10 Hz) at G = 1000
- Wide Supply Range : Operates from ±2.3 V to ±18 V dual supplies
Limitations:
- Bandwidth Limitation : Gain-bandwidth product of 1 MHz may be insufficient for high-frequency applications
- Limited Output Drive : Maximum output current of ±20 mA may require buffering for low-impedance loads
- Temperature Range : Commercial grade (0°C to +70°C) limits use in extreme environments
- Single-Channel : Requires multiple devices for multi-channel systems
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Incorrect Gain Resistor Selection
- Problem : Using standard 5% tolerance resistors causing significant gain error
- Solution : Employ 0.1% or better tolerance metal film resistors
- Calculation : RG = 49.4 kΩ/(G - 1) for desired gain G
Pitfall 2: Poor Power Supply Decoupling
- Problem : Oscillation or noise injection due to inadequate decoupling
- Solution : Place 0.1 μF ceramic capacitors directly at supply pins to ground
- Additional : Use 10 μF tantalum capacitors for bulk decoupling
Pitfall 3: Input Overload Protection
- Problem : Damage from input voltages exceeding supply rails
- Solution : Implement series resistors (1-10 kΩ) and clamping diodes at inputs
- Consideration : Balance protection with noise performance
Pitfall 4: Thermal Considerations
- Problem : Drift in precision applications due to self-heating
- Solution : Ensure adequate PCB copper area for heat dissipation
- Guideline : Maintain junction temperature below 100
