Amplifiers: A Bio amplifier is an electrophysiological device, a variation of the instrumentation amplifier, used to gather and increase the signal integrity of physiologic electrical activity for output to various sources. It may be an independent unit, or integrated into the electrodes.

Bio Amplifiers: electrophysiological device a variation of the instrumentation amplifier used to gather and increase the signal integrity of physiologic electrical activity for output to various sources may be an independent unit, or integrated into the electrodes.

ECG: Low internal noise (<2 mV) High Input Impedance [Zin 10 MV] Bandwidth ranging from 0.16–250 Hz Bandwidth cutoffs (>18 dB/octave). Notch filter (60 Hz, in the United States) Common mode rejection ratio [CMRR > 107] Common mode input range (CMR ± 200 MV) Static electricity shock protection (>2000 V).

EEG: Low internal voltage and current noise(<1 mV, 100 pA) High input impedance (>108 MΩ) Bandwidth (1–50 Hz) Frequency cutoffs (>18 dB/octave) High common mode rejection ratio (>107) Common mode input range (greater than ±200 mV). Static electricity shock protection (>2000 V) Gain stability > ±1%

EMG: Low internal noise (<0.5 mV) High input impedance (>100 MΩ) Flat bandwidth and sharp high and low frequency cutoffs (>18 dB/octave). High common mode rejection ratio (CMRR > 107) Common mode input range (CMR > ±200 mV) Static electricity shock protection (>2000 V) Gain stability > ±1%

Inverting amplifier:

Non inverting amplifier:

Differential Amplifier:

Output voltage of differential amplifier:

Differential mode: Two input signals are equal but have opposite polarity at every instant of time Vo = 2Rf . VD / Ri Common mode: Input voltages appearing at the input terminals 1 & 2 are identical both in amplitude & phase at every instant of time Vo = 0

Operational amplifiers as current source:

CMRR: Common Mode Rejection Ratio Ability of the differential amplifier circuit to ignore the common mode inputs like 50 Hz interference CMRR = amplification of the differential voltage amplification of the common mode voltage CMRR in dB = 20 log10 CMRR

Types of noises present in the amplifier circuits: Noise figure : amount of degradation of the signal (in dB) = ratio of Signal to noise ratio (SNR) at the input To Signal to noise ratio (SNR) at the output For the same frequency bandwidth ∆f

Thermal noise Shot noise Flicker noise Contd.. due to fluctuations in the motion of the charge carriers can be reduced by having bandwidth as small Shot noise Due to current carriers at the electric field Flicker noise Fluctuations in the charge carriers at the surfaces

Isolation amplifier: (pre amplifier isolation circuits) Used to increase the input impedance of the monitoring system in order to isolate the patient from the biomedical instrument Input impedance = 50 M ohms Types: Darlington pair Bootstrapping circuit

Darlington pair: 2 identical transistors are connected in common emitter Zi = β2Zo

Bootstrapping circuit: In cascade emitter follower circuit, a feedback network may be connected between the emitter of II transistor & the collector of I transistor

Bootstrapping circuit:

Isolation amplifier using op amp:

ECG isolation amplifier: Bio signal given to LPF (fc = 10 KHz) filtering reduces the interference caused by electro surgery Higher CMRR Line frequency is eliminated by introducing a notch filter at 50 Hz after the power amplifier CMRR : 115 dB & Zin = 1011 ohms

Contd..

Medical preamplifier design (Instrumentation amplifier): Vo = (V2 – V1)(1+2a)b

Bridge amplifiers: Used to measure the magnitude of the bio signal parameters in terms of current or voltage

Bridge amplifiers: For voltage readout:

Bridge amplifiers: For Current readout:

Single operational amplifier as bridge voltage amplifier:

Line driving amplifier: Transducer with high impedance & its output is so low Load having low impedance We require line driving amplifier between transducer output & load

Line driving amplifier:

Current amplifier: When a source of current is coupled to a load like coil The load requires low input impedance & high currents

Chopper Amplifier: Used to convert the dc and low frequency signal into high frequency signal Followed by conventional ac amplifier Demodulated, filtered Adv: no drift Types: Mechanical chopper amplifier Non mechanical Chopper amplifier

Logic:

Mechanical chopper amplifier:

Non mechanical photoconductive chopper amplifier: