1. What is the key difference between Flip-flop and latch?
Ans. Flip-flop is a synchronous device while latch is asynchronous device i.e. latch doesn’t uses clock and flip flop uses clock. Latch is a combination logic device while flip-flop is sequential device.
2. Explain the difference between DSP processor and general processor.
Ans. DSP(digital signal processor) is a dedicated processor designed specially to execute DSP algorithms faster while a general purpose processor take some execution time for different algorithms as DSP processors are having built in specialized features to aid various DSP algorithm simulations.
3. Why open collector is required for TTL logic gates instead of totem pole output?
Ans. With totem pole output, wired-AND operation is not possible in TTL gates which may lead to transistor burning. With open collector output, wired-AND operation is possible. Hence open collector is preferred than TTL logic gates.
4. If an input is left open in TTL gate then whether it is considered as logic ‘0’ or logic ‘1’?
Ans. It is assumed as logic ‘1’. Since the input is provided at the emitter terminal and open circuiting emitter terminal means that base-emitter junction is reverse-biased.
5. What do you mean by word ‘Digital’?
Ans. Digital means sequence of numbers having finite precision. Digital technology is a base two process. Digitized information is recorded in binary code of combinations of the digits 0 and 1, also called bits, which represent words and images. Digital technology enables immense amounts of information to be compressed on small storage devices that can be easily preserved and transported. Digitization also quickens data transmission speeds.
6. What are Glitches in digital circuits?
Ans. Glitches are appearances of spikes in the output when the input changes. It is due to different turn-on and turn-off times of transistor. Glitches are avoided by using strobe signals.
7. In which type of counters glitches are present and what is the remedy?
Ans. Glitches are appearances of spikes in the output when the input changes. Glitches are present in asynchronous counters and to avoid glitches strobing is done.
8. What is a Johnson counters?
Ans. Johnson counter also known as creeping counter, is an example of synchronous counter. In Johnson counter, the complemented output of last flip flop is connected to input of first flip flop and to implement n-bit Johnson counter we require n flip-flop.It is one of the most important type of shift register counter.
9. What is differential non-linearity? Explain.
Ans. Deviation of actual step size from the ideal step size corresponding to 1 LSB is called differential non-linearity.
10. Why the received echos are divided into I and Q components? What is I and Q here?
Ans. In order to find the direction of Doppler shifts i.e. +ve or -ve the received echos are divided into I and Q components. I is in phase component and Q is quadrature component.In communication system also the noise is divided into I and Q components.
11. Present days mobile use which type of memory?
Ans. Flash type memory is used in mobile phones. Flash memory is a non-volatile memory chip used for storage and for transferring data between a personal computer (PC) and digital devices. It has the ability to be electronically reprogrammed and erased. It is often found in USB flash drives, MP3 players, digital cameras and solid-state drives.
12. Give atleast 4 DC specification of an analog to digital converter.
Ans. Gain Error, Offset Error, Integral Non Linearity, Differential Non Linearity.
Analog-to-Digital Converter (ADC) gain error is defined as the deviation of the last step’s midpoint of the actual ADC from the last step’s midpoint of the ideal ADC, compensating for offset error. After compensating for offset errors, applying an input voltage of 0 always results in an output value of 0. However, gain errors cause the actual transfer function slope to deviate from the ideal slope. This gain error can be measured and compensated for by scaling the output values.
Offset error, often called 'zero-scale' error, indicates how well the actual transfer function matches the ideal transfer function at a single point.
Integral Nonlinearity (INL) Error
For data converters, INL is the deviation of an actual transfer function from a straight line. After nullifying offset and gain errors, the straight line is either a best-fit straight line or a line drawn between the end points of the transfer function. INL is often called 'relative accuracy.'
Differential Nonlinearity (DNL) Error
For an ADC, the analog-input levels that trigger any two successive output codes should differ by one LSB (DNL = 0). Any deviation from one LSB is defined as DNL. For a DAC, DNL error is the difference between the ideal and the measured output responses for successive DAC codes. An ideal DAC response would have analog output values exactly one code (LSB) apart (DNL = 0).
13. What is meant by integral nonlinearity (INL)?
Ans. Maximum deviation in LSBs from ideal ADC transfer function is known as INL.
For data converters, INL is the deviation of an actual transfer function from a straight line. After nullifying offset and gain errors, the straight line is either a best-fit straight line or a line drawn between the end points of the transfer function. INL is often called 'relative accuracy.'
14. What is the difference between latches and flip-flop based design?
Ans. Latches are level sensitive while flip-flop are edge sensitive.
15. What is meant by current hogging? Which logic family has the problem of current hogging?
Ans. Current hogging problem is due to difference in the characteristics of the transistor. Due to these differences, the saturation voltage of the load transistor may be different. So when one transistor enter into saturation it will not allow other transistor to enter saturation and will take whole of the current supplied from the driver gate. This is known as current hogging. DCTL(Direct coupled Transistor Logic) has the problem of current hogging.
16. Which saturated logic family is suitable for Large Scale Integration (LSI)?
Ans. Integrated Injection Logic (I2L) is the only saturated bipolar logic suitable for LSI because of small silicon chip area required and low power consumption. The PNP and NPN transistors are used simultaneously thus easing fabrication.
17. Which logic family has lowest speed power product?
Ans. CMOS has the lowest speed power product (i.e. FOM figure of merit) and required very small power.
18. Give advantage and disadvantage of High threshold Logic (HTL).
Ans. Advantages of HTL: Increased Noise Margin, Spike Control, High Noise Threshold Value.
Disadvantages: Slow speed due to increased supply voltage resulting in use of high value resistors, High power drawn.
19. What do you understand by complements of any number?
Ans. Complements are used to simplify the subtraction operation in digital computers. For each radix-r system there are two types of components.
Radix complement → r’s complement.
Diminished radix complement → (r - 1)’s complement.
20. What is Gray code? Where is it used?
Ans. Gray code is a numerical code used in computing in which consecutive bits are represented in binary numbers differing in only one bit. In the reduction of expression using K map, in K map gray codes are used.
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