Right-Leg-Driven Circuit and Instrumentation Amplifier in ECG Acquisition System

In an ECG (Electrocardiogram) acquisition system, instrumentation amplifiers are commonly used to amplify the small electrical signals generated by the heart and reject common-mode noise. The term "Right-Leg-Driven Circuit" (RLD) is a technique used to improve the common-mode rejection ratio (CMRR) in instrumentation amplifiers, specifically in ECG applications where high CMRR is crucial for accurate signal acquisition.
Here's an overview of how a Right-Leg-Driven Circuit and an Instrumentation Amplifier are used in an ECG acquisition system:
Instrumentation Amplifier (IA):
An Instrumentation Amplifier is a differential amplifier with high input impedance and high common-mode rejection capability. It amplifies the voltage difference between two input terminals (ECG electrodes in this case) while rejecting any common-mode signals (such as interference or noise) that are present on both input terminals.
The IA typically consists of three operational amplifiers (Op-Amps) configured to provide the desired amplification and filtering.
Right-Leg-Driven Circuit (RLD):
The Right-Leg-Driven Circuit is a technique used to reduce the common-mode voltage at the patient's right leg electrode. This is important because the reference electrode (usually the right leg electrode) should ideally have a common-mode voltage close to the patient's common-mode voltage to ensure accurate ECG measurements and patient safety.
RLD works by actively driving the right leg electrode to match the common-mode voltage of the patient. This is usually done using an auxiliary electrode placed on the patient's right leg and a feedback loop to maintain the voltage at the right leg electrode close to the patient's common-mode voltage.
The RLD circuit is connected to one of the inputs of the instrumentation amplifier to effectively subtract the common-mode voltage from the ECG signal, further improving CMRR.
The combined use of an Instrumentation Amplifier and a Right-Leg-Driven Circuit helps achieve high common-mode rejection and accurate ECG signal acquisition by:
Amplifying the small differential ECG signal.
Rejecting common-mode noise and interference.
Reducing the common-mode voltage at the right leg electrode to minimize the risk of electrical shock to the patient and to ensure accurate measurements.
ECG acquisition systems are critical for monitoring heart health, and these techniques are essential to obtain reliable and accurate ECG waveforms while maintaining patient safety by minimizing common-mode voltage differences. Implementing such systems requires careful design and consideration of electrode placement, amplifier characteristics, and signal processing techniques to achieve optimal performance.

1. Presentation ।। BMPT521 Right-Leg-Driven Circuit and Instrumentation Amplifier in ECG Acquisition System Presented by Jewel Haque Munshi Graduate Student (MS) BMPT, DU, Dhaka-1000 03/09/2023 ‹#›

2. Slide Contents Introduction RLD Circuit RLLD Circuit Cont… Instrumentation Amplifier Instrumentation Amplifier Cont… Importance Conclusion Reference ‹#›

3. Introduction Biosignals i.e. potentials, voltages, and electrical field strengths from nerves and muscles, are typically recorded at very low levels, ranging from micro to millivolts, and often exhibit high source impedances.Consequently, amplification becomes essential. In ECG acquisition systems, IAs are employed to amplify the faint electrical signals originating from the heart, with the Right-Leg-Driven Circuit (RLD) to enhance the common-mode rejection ratio (CMRR) ‹#›

4. RLD works by actively driving the right leg electrode to match the common-mode voltage of the patient. This is usually done using an auxiliary electrode placed on the patient's right leg and a feedback loop to maintain the voltage at the right leg electrode close to the patient's common-mode voltage RLD Circuit A technique used to reduce the common-mode voltage at the patient's right leg electrode. The RLD circuit is connected to one of the inputs of the instrumentation amplifier to effectively subtract the common-mode voltage from the ECG signal, further improving CMRR. ‹#›

5. RLD Circuit Fig.: Driven Right Leg Circuit for ECG ‹#›

6. Instrumentation Amplifier An IA is a differential amplifier with High input impedance and High common-mode rejection capability. Amplifies the voltage difference between two input terminals (ECG electrodes in this case) while rejecting any common-mode signals (such as interference or noise) that are present on both input terminals. ‹#›

7. Instrumentation Amplifier Fig.: Instrumentation Amplifier in ECG Circuit ‹#›

8. Importance Amplifying the small differential ECG signal. Rejecting common-mode noise and interference. Reducing the common-mode voltage at the right leg electrode to minimize the risk of electrical shock to the patient and to ensure accurate measurements. ‹#›

9. ECG acquisition systems are critical, and these techniques are essential to obtain reliable and accurate ECG waveforms while maintaining patient safety by minimizing common-mode voltage differences. Careful design and consideration of electrode placement, amplifier characteristics, and signal processing techniques to achieve optimal performance is important. Conclusion ‹#›

10. Reference [1] Jason Waechter “Introduction to EC ’s: Rhythm Analysis” MD FRCPC Clinical Assistant Professor Depts. of Anesthesia and Critical Care Written in 1999 Last Revised July/2013© 2013. [2] Lacirignola, F. and Pasero, E. (2017), Hardware design of a wearable ECG-sensor: Strategies implementation for improving CMRR and reducing noise, 2017 European Conference on Circuit Theory and Design (ECCTD), pp. 1-4 [3]Martin J. Bur e* and Denis T. leeson “A Micropower Dry-Electrode ECG Preamplifier" IEEE transactions on biomedical engineering, vol. 47, no. 2, february 2015. ‹#›

11. Thank you for y our time and attention 🙂 ‹#›