Chapter 3: Digital Logic Structures Flashcards
MOS Transistors
(metal-oxide semiconductor) Makes or breaks a closed circuit Two-Types: p-type n-type Both operate logically (i.e. like switches)
3 Terminals of a MOS Transistor
gate
source
drain
n-type transistor
Closed circuit if _______
Open circuit if _______
Closed: some amount of voltage (i.e. 2.9 volts)
Open: 0 volts
p-type transistor
Closed circuit if _______
Open circuit if _______
Opposite (i.e. complementary) to n-type transistor
Closed: 0 volts
Open: some amount of voltage (i.e. 2.9 volts)
CMOS circuits
contain both n-type and p-type transistors
Complementary Metal-Oxide Semiconductor
NOT gate
aka “Inverter”
an electronic circuit that implements the NOT logic function.
NOR gate
an electronic circuit that implements the NOT-OR logic function.
(exactly the opposite of the OR function)
OR gate
an electronic circuit that implements the OR logic function.
achieved by adding an inverter (NOT gate) to a NOR gate.
AND gate
an electronic circuit that implements the AND logic function.
achieved by adding an inverter (NOT gate) to a NAND gate.
NAND gate
an electronic circuit that implements the NOT-AND logic function.
DeMorgan’s Law
“it is not the case that both A and B are false” is equivalent to “at least one of A and B is true”
(see paper note-card for symbolic representation)
An n-input AND gate has an output value of 1 only if ____ n input variables have values of __.
ALL
1
An n-input OR gate has an output value of 1 if ____ of the n input variables has a value of __.
ANY
1
An n-input OR gate has an output value of 0 only if ____ n input variables have values of __.
ALL
0
An n-input AND gate has an output value of 0 if ____ of the n input variables has a value of __.
ANY
0
Two kinds of logic structures:
1) store information
2) do not store information
Decision Elements
aka: combinational logic structures
Logic structures that do not store information.
Outputs are strictly dependent on the combination of input values that are being applied to the structure right now.
Not at all dependent on any past history of information that is stored internally, since no info can be stored internally in this type of circuit.
(e.g. Decoder, Mux, Full Adder)
Decoder
exactly one output is 1 and all the rest are 0s.
In general: has n inputs and 2^n outputs.
In a Decoder, the output line that detects the the input pattern (i.e. the line that has an output of 1) is _______.
asserted
Mux
two-input multiplexer
Function is to select one of the inputs and connect it to the output.
In general: consists of 2^n inputs and n select lines.
The Select Signal in a Mux determines ________
which input is connected to the output.
i.e. if S = 0, that input is NOT connected to the output in the example on p.61., if S = 1 then that input IS connected to the output.
Full Adder
A logic circuit that provides 3 inputs and 2 outputs
Programmable Logic Array (PLA)
an array of AND gates followed by an array of OR gates.
The number of AND gates corresponds to the number of input combinations (rows) in the truth table.
The number of OR gates corresponds to the number of output columns.
Logical Completeness
Any logic function can be accomplished as long as there are enough AND, OR, and NOT gates available.
(i.e. the set of gates {AND, OR, NOT} is logically complete because sufficient to build a logic circuit for any truth table)
