Digital circuits Flashcards
What is an inverter or a NOT gate?
This gate outputs the inverse of its input.
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.
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
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
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
Show how to create a D-Latch using Tx gates and inverters
As shown
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.
Draw the operation table for the D-latch
Draw the Master-Slave arrangement of D-latches required to produce a D flip-flop
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.
