UNIT IV - SPECIAL ICs
1. Define conversion time.
It is defined as the total time required to convert an analog signal into its digital output. It
depends on the conversion technique used & the propagation delay of circuit components. The
conversion time of a successive approximation type ADC is given by
T(n+1)
where T---clock period
Tc---conversion time n----no. of bits
2. Define resolution of a data converter.
The resolution of a converter is the smallest change in voltage which may be produced at the
output or input of the converter.
Resolution (in volts)= VFS/2n-1=1 LSB increment. The resolution of an ADC is defined as the
smallest change in analog input for a one bit change at the output.
3. Define accuracy of converter.
Absolute accuracy:
It is the maximum deviation between the actual converter output & the ideal
converter output.
Relative accuracy:
It is the maximum deviation after gain & offset errors have been removed.
The accuracy of a converter is also specified in form of LSB increments or % of full scale
voltage.
4. What is settling time?
It represents the time it takes for the output to settle within a specified band ±½LSB of its
final value following a code change at the input (usually a full scale change). It depends upon the
switching time of the logic circuitry due to internal parasitic capacitance & inductances. Settling
time ranges from 100ns. 10µ s depending on word length & type circuit used.
5. Explain in brief stability of a converter:
The performance of converter changes with temperature age & power supply variation . So all
the relevant parameters such as offset, gain, linearity error & monotonicity must be specified
over the full temperature & power supply ranges to have better stability performances.
6. What is meant by linearity?
The linearity of an ADC/DAC is an important measure of its accuracy & tells us how close
the converter output is to its ideal transfer characteristics. The linearity error is usually expressed
as a fraction of LSB increment or percentage of full-scale voltage. A good converter exhibits a
linearity error of less than ±½LSB.
7. What is monotonic DAC?
A monotonic DAC is one whose analog output increases for an increase in digital input.
8. What is multiplying DAC?
A digital to analog converter which uses a varying reference voltage VR is called a
multiplying DAC(MDAC). If the reference voltage of a DAC, VR is a sine wave give by
V(t)=Vin Cos 2 ft
Then, Vo(t)=VomCos(2 ft + 180º)
9. What is a sample and hold circuit? Where it is used?
A sample and hold circuit is one which samples an input signal and holds on to its last
sampled value until the input is sampled again. This circuit is mainly used in digital interfacing,
analog to digital systems, and pulse code modulation systems.
10. Define sample period and hold period.
The time during which the voltage across the capacitor in sample and hold circuit is equal to
the input voltage is called sample period. The time period during which the voltage across the
capacitor is held constant is called hold period.
11. What is meant by delta modulation?
Delta modulation is a technique capable of performing analog signal quantization with
smaller bandwidth requirements. Here, the binary output representing the most recent sampled
amplitude will be determined on the basis of previous sampled amplitude levels.
12. Draw the Pin digram of IC 555.
13. Mention some applications of 555 timer:
Oscillator
pulse generator
ramp and square wave generator
mono-shot multivibrator
burglar alarm
Traffic light control.
14. List the applications of 555 timer in monostable mode of operation:
Missing pulse detector
Linear ramp generator
Frequency divider
Pulse width modulation.
15. List the applications of 555 timer in Astable mode of operation:
FSK generator
Pulse-position modulator
16. List the applications of 555 timer in monostable mode of operation:
Missing pulse detector
Linear ramp generator
Frequency divider
Pulse width modulation.
17. List the applications of 555 timer in Astable mode of operation:
FSK generator
Pulse-position modulator
18. What is a voltage regulator?
A voltage regulator is an electronic circuit that provides a stable dc voltage
independent of the load current, temperature, and ac line voltage variations.
19. Give the classification of voltage regulators:
Series / Linear regulators
Switching regulators.
