16
|
How many flip flops are required for 2N
count?
|
|
One flip flop count up to 2 pulses, two flip flops
count up to 22 = 4 pulses. Similarly N flip flop count up to 2N
pulses.
|
17
|
What to do
for invalid states in the synchronous and asynchronous counter?
|
|
The synchronous and asynchronous counter goes from
invalid state to valid state by providing external logic circuit which
properly reset each flip flop.
|
18
|
Explain
the lock out state of the counter.
|
|
Lock out
- The counter
may move from one unused state to other unused state and never come to its
valid state is called as lock out state of the counter.
- The lock out
problem occurs due to noise spikes.
- This counter
becomes useless.
|
19
|
Explain
the term : Forward / Backward counter
|
|
Forward / Backward
counter ( Bi- directional counter )( UP / DOWN counter )
- It is a
counter which can count in both upward and downward directions.
|
20
|
Why the
skipping of state may occurs in the asynchronous counter?
OR
Write the
relation between propagation delay time and clock frequency. What is
importance of propagation delay time?
|
|
The relation between propagation delay and clock
frequency is
fc
< ( 1 / ntpd )
fc = Clock frequency
n =
Number of stages and
tpd
= Propagation delay time
Importance of propagation delay time
- The propagation delay time imposes a limit on
frequency at which the counter can be clocked in the ripple counter.
|
21
|
Why the
ripple counters are connected in cascaded? How cascaded connection is done?
|
|
Cascaded connection of ripple counter
- The ripple counters are connected in cascaded in
order to increase the modulus of the counter.
- The cascading of the counter is done by connecting
the most significant stage of the first counter to the toggling stage of the
second counter.
|
22
|
Explain
the term : Decoding of the counter, Glitches of the counter, Strobing
|
|
Decoding of the counter
- The decoding
of the counter is done by decoder or gates.
- The output of
the counter is in the binary form and it is converted in the decoding form by
a decoder.
Glitches of the counter
- The
transitional states in the asynchronous counter produces undesirable voltage
spikes of short duration at the output of the decoder is called as the
glitches.
- The transition
state is creating by propagation delay.
Strobing
- It is a method to eliminate glitches.
- The glitch can eliminate by enabling the decoder
output at a time after glitches have had time to disappear.
- This can be achieved by using LOW level of the clock
to enable the decoder.
|
23
|
Which gate
is used for active HIGH decoding and active LOW decoding?
|
|
AND gate
|
24
|
What is
width of glitches in the counter?
|
|
The width of glitches is equal to width of the
propagation delay.
|
25
|
How the
glitch affect if the decoder output drive edge triggered circuit? How to
reduce it?
|
|
Effect of Glitches
- If the decoder output drives edge triggered circuit,
the glitch produces unsatisfactory performance.
- This effect is reduced by ANDing the decoder with
the clock.
- However this will reduce the width of deglitched
output to the width of clock pulse which causes gaps between decoder outputs.
|
26
|
Why the
asynchronous counters are slow?
|
|
The asynchronous counters are slow because each flip
flop can change state only if all the preceding flip flops have changed their
state.
|
27
|
What is
synchronous counter?
|
|
Synchronous counter
- It is a
counter in which all the flip flops are triggered simultaneously.
|
28
|
Give reason
: The clock frequency of the asynchronous counter should be low.
|
|
Clock frequency of the asynchronous counter
- If the clock frequency of the asynchronous counter
should be high, the counter may skip some of the states and malfunction
occurs.
|
29
|
Why the
synchronous counter can be operated at much higher frequency than the
asynchronous counter?
|
|
Synchronous counter
- The
propagation delay of the synchronous counter is equal to propagation delay of
the single flip flop and gates.
- Therefore the
synchronous counter can be operated at high frequency.
Asynchronous counter
- The
propagation delay of the asynchronous counter is equal to propagation delay
of all flip flops.
|
30
|
Describe
the advantages and disadvantages of the synchronous counter.
|
|
Advantages
- High speed
- Less severe decoding problem
Disadvantages
- It requires more circuit as compared to asynchronous
counter.
|
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