QUESTION BANK ANSWERS (2 MARKS)
147404 - LINEAR INTEGRATED CIRCUITS
APPLICATIONS OF OPERATIONAL AMPLIFIERS
1. Give some applications of Comparator.
a. Zero crossing detector b. Window detector
c. Time marker generator d. Phase detector
2. What is a window detector?
A device, usually consisting of a pair of voltage comparators, in which output indicates whether the measured signal is within the voltage range bounded by two different thresholds (an "upper" threshold and a "lower" threshold).
3. List the types of comparators.
4. Differentiate Schmitt trigger and comparator.
A Schmitt trigger is a comparator with a small amount of positive feedback applied to create a hysteresis for the input level.
5. What are the limitations of an ideal active differentiator?
At high frequency, differentiators may become unstable and break into oscillation. The input impedance i.e. (1/ωC1) decreases with increase in frequency, thereby making the circuit sensitive to high frequency noise.
6. State the important features of an instrumentation amplifier.
a. high gain accuracy b. high CMRR
c. high gain stability with low temperature co-efficient d. low dc offset
e. low output impedance
7. How does the precision rectifier differ from the conventional rectifier?
These rectifiers are used to rectify very small voltages or currents for which the diode never gets forward biased in the conventional one. i.e. voltage or currents are always less than .7V which can not be rectified by normal rectifiers.
This rectifier doesn’t give any kind of drop in output since diodes are previously biased using op-amp.
8. What are the advantages of active filters over the passive filters?
Active filters use amplifying elements, especially op amps, with resistors and capacitors in their feedback loops, to synthesize the desired filter characteristics. Active filters can have high input impedance, low output impedance, and virtually any arbitrary gain.
They are also usually easier to design than passive filters. Possibly their most important attribute is that they lack inductors, thereby reducing the problems associated with those components.
9. Draw the freq. response of the LPF.
10. What is an antilog amplifier? Draw the circuit of an antilog amplifier.
Antilog amplifier is a decoding circuit to convert a logarithmically encoded signal back to the real signal.
11. What is a V to C convertor?
A transconductance amplifier (gm amplifier) puts out a current proportional to its input voltage. In network analysis, the transconductance amplifier is defined as a voltage controlled current source (VCCS) .
For direct current, transconductance is defined as follows:
12. Draw the circuit of an integrator.
13. Why integrators are preferred over differentiators in analog computers?
Integrators are more linear than the differentiators and the integrators reduce the power consumption than the high pass filter.