You can get the idea about Carrier Amplifier, Lock-in amplifier, Chopper Amplifier, Advantages, Applications

1. 1

2. Types of Bio Amplifiers
2
Operational
Amplifier
Differential
Amplifier
Instrumentation
Amplifier
Isolation
Amplifier
Carrier
Amplifier
Chopper
Amplifier

3. CARRIER AMPLIFIER
■ A direct-current amplifier
■ The dc input signal is filtered by a lowpass
filter, then used to modulate a carrier so it
can be amplified conventionally as an
alternating-current signal;
■ The amplified dc output is obtained by
rectifying and filtering the rectified carrier
signal.
3

4. ❖ Oscillator is used to energize the transducer with an alternating carrier voltage.
Transducers require ac excitation and whose impedance is not purely resistive.
❖ Transducer shall change the amplitude of the carrier voltage in relation to changes in
the physiological variable being measured.
■ Output of transducer would be an amplitude modulated signal.
■ Modulated signal is given to multi stage capacitance coupled amplifier
■ First stage produces amplification of AM signal
■ Second stage is constructed that it can respond only to signal frequency of the carrier. It
can be further amplified in the following stage
4

5. ■ Then signal is demodulated in phase sensitive demodulator circuit. It helps to
extract amplified signal voltage after filter circuit. The voltage produced by the
demodulator can then be applied to the driver stage of the writing system.
❖ Carrier amplifiers can be used with a resistance strain gauge transducer such as a
semiconductor strain gauge.
■ When used with pressure gauges, a calibration control is provided on the carrier
amplifier.
5

6. Lock-in amplifier
■ Lock-in amplifier is a useful version of the carrier technique designed for
the measurement of low-level signals buried in noise.
ADVANTAGES:
■ It reduces wideband noise and increases the signal-to noise ratio.
■ This permits the signal to be recovered from its noisy background.
6

7. CHOPPER AMPLIFIER
■ Chopper circuit is used to refer to numerous types of electronic switching
devices and circuits used in power control and signal applications
■ Chopper stabilizes a system against drift of electronic components
7

8. CHOPPER AMPLIFIER
■ The chopper amplifier is a useful device
in the field of medical field.
■ It gives another solution to the problem
of achieving adequate low frequency
response while avoiding the drift
problem inherent in direct coupled
amplifiers.
8

9. ■ This type of amplifier makes use of a chopping device, which converts a slowly varying
direct current to an alternating form with amplitude proportional to the input direct
current and with phase dependent on the polarity of the original signal.
■ The alternating voltage is then amplified by a conventional ac amplifier whose output is
rectified back to get an amplified direct current.
■ A chopper amplifier is an excellent device for signals of narrow bandwidth and reduces
the drift problem.
■ Chopping the low frequency components of the input signal, amplifying this chopped
signal in an ac amplifier (A1) and then demodulating the output of the ac amplifier
9

10. ■ Low frequency components are derived from the input signal by passing
it through the low-pass filter, consisting of R2, C2 and R2
■ The filtered output is then further amplified in a second stage of dc
amplification (A2).
■ Minor offsets and bias currents exist due to imperfect chopping, but these
are extremely small.
■ Switch-driving oscillator built on the module
10

11. To avoid noise:
■ It is desirable to design the feedback networks and external wiring to minimize the total circuit noise.
■ It is advisable that a feedback capacitor be used to limit the overall bandwidth and eliminate as much
high frequency noise as possible.
■ Shielding of feedback components is desirable in chopper amplifiers
■ It is particularly necessary in electrically noisy environments. Use of shielded wire for summing
junction leads is also recommended. Typical voltage drift in chopper-stabilized amplifiers is 0.1
mV/°C and current drift as 0.5 pA/°C.
11

12. Advantages
■ The great strength of the chopper-stabilized amplifier is its insensitivity
to component changes due to ageing, temperature change, power supply
variation or other environmental factors
■ Chopper amplifiers are available in both single ended as well as
differential input configurations.
12

13. Applications
■ Used in medical field in amplification of small dc signals. Such order of
amplitudes are obtainable from transducers such as strain gauge pressure
transducers, temperature sensors.
■ A chopper amplifier is also suitable for use with a thermocouple
13

14. 14