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Flashcards in Digital circuits Deck (10):
1

What is an inverter or a NOT gate?

This gate outputs the inverse of its input.

2

What is significant about two inverters connected with feedback?

It creates a stable loop which adopts one of two configurations. This saved value is useful in constructing logic circuits.

3

What is this?

When does it conduct?

How well does it conduct when the inputs are high/low?

Is it used in pull-up or pull-down networks?

An NMOS transistor

On when G is high

Poor conduction if A/B high

Good conduction if A/B low

Used in Pull-down networks

4

What is this?

When does it conduct?

How well does it conduct when the inputs are high/low?

Is it used in pull-up or pull-down networks?

A PMOS transistor

On when G is low

Good conduction if A/B high

Poor conduction if A/B low

Used in Pull-up networks

5

How do you make a digital switch that can be opened/closed using a control signal G?

Use an NMOS and a PMOS to create a Tx (transmission) gate as shown

6

Show how to create a D-Latch using Tx gates and inverters

As shown

7

Describe the operation of the D-latch:

While G is high

On the high-low falling edge

While G is low

While G is high the D-latch is in transparent mode where the feedback loop is open and the output Q is simply the input D.

On the high-low edge the current Q output is 'frozen' and ignores any further D input changes

While G is low the D-latch is in memory mode and outputs the captured value, regardless of input D.

8

Draw the operation table for the D-latch

9

Draw the Master-Slave arrangement of D-latches required to produce a D flip-flop

10

Describe the operation of the D flip-flop when

The clock is low

The low-high transition

The clock is high

in terms of the master-slave arrangement

When the clock is low the Master is transparent and the Slave retains its memorised output Q

On the low-high transition the Master stores the input D, while the Slave is transparent. This value is passed to the Slave to output.