BioElectronics Basics: Amplification BioElectronics Basics ...
EMBE401D: Instrumentation & Analysis Week 2 Lecture 1: Bioelectronics Fundamentals Part 1
BioElectronics Basics: Amplification • Biomedical signals have small amplitudes and require amplification • They are often corrupted by noise that can be removed by clever designs. ECG amplifier
BioElectronics Basics: Amplification Types Single-ended (two-wire)
Differential (three wires)
Differential (two wires)
1
BioElectronics Basics: Inverter Single-ended inverting amplifier
BioElectronics Basics: Amplification Non-inverting single ended amplifier
ECG With Single Ended Amplifier Recording with single-ended amplifier. A 60Hz waveform Is recorded instead of the ECG Why?
2
ECG With Single Ended Amplifier Assuming Rs=10K Vout = 720mV This number is much greater that the expected amplitude of the ECG: 1mV*10= 10mV Vout =
10Rs 120 1 + 2Rs jcw
Nout =
10xRs .120C w
(
1+ 2RsC w
)
2
Common Mode Signal The 60 Hz signal observed is common to both arms and is called the common mode signal (VC) By subtracting VA from VB we can: • Recover the differential signal VD (ECG in this case) • Eliminate the common mode signal VC
Differential And Common Mode Gains For a differential amplifier as shown below:
3
ECG With Operational Amplifier An operational amplifier cannot be used to amplify the ECG signal. Why?
Finite Gain Differential Amplifier The amplifier must be linear and therefore we can use superposition to calculate A and B 1) Set VB=0 and calculate A 2) Set VA=0 and calculate B
Differential Amplifier: Calculation of gain A If VB=0 the circuit becomes:
4
Differential Amplifier: Calculation Of gain B If VA=0 the circuit becomes:
Differential Amplifier FINITE GAIN The total gain is therefore
Differential Amplifier Simplified Assuming that R2/R1=R4/R3 we have:
5
High Impedance Differential Amplifier To increase the input impedance: add buffers
Differential Amplifier Input Stage
Instrumentation Amplifier
6
Available Instrumentation Amplifiers Instrumentation amplifiers are commercially available. The specifications the AD8421, a low-cost, fast amplifier. The specifications are available on the web.
http://pdf1.alldatasheet.com/datasheet-pdf/view/455827/AD/AD8421.html
7
BioElectronics Basics: Amplification • Biomedical signals have small amplitudes and require amplification • They are often corrupted by noise that can be removed by clever designs. ECG amplifier
BioElectronics Basics: Amplification Types Single-ended (two-wire)
Differential (three wires)
Differential (two wires)
1
BioElectronics Basics: Inverter Single-ended inverting amplifier
BioElectronics Basics: Amplification Non-inverting single ended amplifier
ECG With Single Ended Amplifier Recording with single-ended amplifier. A 60Hz waveform Is recorded instead of the ECG Why?
2
ECG With Single Ended Amplifier Assuming Rs=10K Vout = 720mV This number is much greater that the expected amplitude of the ECG: 1mV*10= 10mV Vout =
10Rs 120 1 + 2Rs jcw
Nout =
10xRs .120C w
(
1+ 2RsC w
)
2
Common Mode Signal The 60 Hz signal observed is common to both arms and is called the common mode signal (VC) By subtracting VA from VB we can: • Recover the differential signal VD (ECG in this case) • Eliminate the common mode signal VC
Differential And Common Mode Gains For a differential amplifier as shown below:
3
ECG With Operational Amplifier An operational amplifier cannot be used to amplify the ECG signal. Why?
Finite Gain Differential Amplifier The amplifier must be linear and therefore we can use superposition to calculate A and B 1) Set VB=0 and calculate A 2) Set VA=0 and calculate B
Differential Amplifier: Calculation of gain A If VB=0 the circuit becomes:
4
Differential Amplifier: Calculation Of gain B If VA=0 the circuit becomes:
Differential Amplifier FINITE GAIN The total gain is therefore
Differential Amplifier Simplified Assuming that R2/R1=R4/R3 we have:
5
High Impedance Differential Amplifier To increase the input impedance: add buffers
Differential Amplifier Input Stage
Instrumentation Amplifier
6
Available Instrumentation Amplifiers Instrumentation amplifiers are commercially available. The specifications the AD8421, a low-cost, fast amplifier. The specifications are available on the web.
http://pdf1.alldatasheet.com/datasheet-pdf/view/455827/AD/AD8421.html
7
