TTL Characteristics Flashcards
what are the two sets of dc parameters?
voltages and currents
What are the process manufacturing tolerances in DC paremeters and fanout?
V.il, V.ol, V.ih, V.oh
V.il: Guaranteed maximum low-level (L) input voltage allowed for reliable gate operation
V.ol: Guaranteed maximum low level output voltage allowed for reliable gate operation
…anything with an h is “guaranteed minimum high level output/input voltage”
v.il-v.ol = ?
low level dc noise margin
same with dc high level noise margin
output voltage transients may venture into the nosie margin region without jeopardizing reliable operation
What are the process manufacturing tolerances in DC parameters and fanout as it pertains to circuits?
I.il, I.ol, I.ih, I.oh
What is fanout?
a system parameter: number of input circuits one output circuit can drive
What is high level fanout equation?
I.oh/I.ih
What is low level fanout?
I.ol/I.il
As the input voltage Vin falls from +5 volts, the current flowing into the circuit is I.ih, which is what?
the sum of the reversed bias diode current plus leakage.
As V.in falls below 1.4 volts, what happens?
the current reverses to become I.il (guarnteed max low level input for reliable gate operation) and the forward diode current begins
As V.in falls below 1.0 V, what happens?
the current increases linearly because the diode acts like a .4v battery.
I.il is at its maximum when what happens?
input ovltage V.in is at ground (zero volts)
If V.in goes negative, what happens?
the input shunt diode turns on when V.in passes .4 v and only V.in source impedance limits the current
Why is the input current less than 20 microamperes and less than .4 milliamp at L input voltage?
H and L input currents are very different. This is a cumuliative answer.
A shottky clamped output transistor with grounded emitter is equialent to a what?
a resistor as the collector voltage rises from zero with base current fixed.
L equivalent output circuit is a .2 v batter in series with a 16.3 ohm resistor
L equivalent output circuit is a .2 v batter in series with a 16.3 ohm resistor
V.ol at 0.5 v is the what of the L region? upperbound or lower bound?
is the specified upper bound of the L region
value taken fro a 74LS TTYL low level output characteristic
H Level Output: H equivalent output circuit is a 3.6v battery in series with a 92 ohm resistor
H Level Output: H equivalent output circuit is a 3.6v battery in series with a 92 ohm resistor
H Level Output: H equivalent output circuit is a 3.6v battery in series with a 92 ohm resistor
H Level Output: H equivalent output circuit is a 3.6v battery in series with a 92 ohm resistor
Transistors Q.4a and Q.4b form a darlington circuit. What’s that?
a low output impedance circuit
What is a gate transfer function?
It defines the output voltage as a function of the input voltage.
When does the output usually change state?
When the input traverses from the invalid region from L to H or H to L.
A digital gate is a low-fidelity linear amplifier when the input is in…
in the digital invalid region.
What are guaranteed switching speed parameters?
Propagation delay times from gate input transitions to gate output transitions.
What are gate output transitions?
Delayed gate input transitions
A designer doesn’t pay attention to maximum values for propogation delay times, true or false?
False, they do pay attention.
Repeat the following: the setup and hold time requirements are consistent with the assumptions of fundamental mode asynchronous circuit design
Repeat the following: the setup and hold time requirements are consistent with the assumptions of fundamental mode asynchronous circuit design
Enabling a connection when connected to the gate load when the enable control changes the output impedance from an open circuit to a what?
to a standard gate output.
What is ringing?
damped sinusoidal oscillation following a high to low transition in a waveform
how is ringing determined?
by load capacitance, and the inductance of the wiring
true or false: damping is set by resistive loading
true, series resistors that are external to a gate output provide additional damping
why does ringing limit the switch rate prematurely?
because ther ringing must die out before the next switching transition occurs.
Watch for simultaneous switching of inactive outputs. But why?
the voltage induced by ground lead inductance raises the potential of inactive output pins
packages with short leads externally and internally significantly reduce inductance. what is inductance?
the property of a circuit or electric conductor to generate an electromotive force by a change in the current flowing. Units are H (henrys)
