Implementation of digital electronics Flashcards
What is TTL?
Transistor-transistor logic where both input and outputs are constricted with transisitors
Define STTL and its purpose
Schottky TTL- where the switching speed of TTL is improved by adding a diode
Define LSTTL
Low Power Schottky TTL- inherits speed improvement of the STTL but reduced power
Define CMOS
Complimentary Metal-oxide Semiconductor- FET based logic with lower power consumption than BJTs
-low switching speed
Define HCMOS
High speed CMOS
HTCMOS
High speed TTL compatible CMOS
Compare TTL gates to CMOS gates
CMOS has a much lower power consumption due to little current used in the FETs.
TTL is much faster than CMOS.
Define fanout
the number of inputs that can driven by a single output
Give an example of a CMOS gate and its characteristics
4011B
-FET technology
-Supply current = 0.125nA and voltage = 2-6V
-propogation delay 125ns at 5V
How does a diode OR gate work
the diode acts as a short circuit so the 5V appears across the resistor
Define passive pull-up
When we need a HIGH only the passive device is available so the resistor creates an output similar to an open circuit
Define active pull-up
Forcing a HIGH or LOW by switching on/off an active device
How can TTL circuits be improved?
a Schottky barrier diode can be used to turn off TTL gates quicker
-schottky diodes have low voltage drops and short reverse recovery time
How do MOSFETS act as switches?
When the drain is coneected to the source, the MOSFET is ON.
- When the drain is disconnected, the MOSFET is off
why digital over analogue logic?
Digital logic is more immune to noise and uses thresholds of voltages to reach a HIGH or LOW state
