Digital Electronics-Integrated-CircuitLogic Families
Digital Electronics-Integrated-CircuitLogic Families
11. What must be done to interface CMOS to TTL?
- A dropping resistor must be used on the CMOS 12 V supply to reduce it to 5 V for the TTL.
- As long as the CMOS supply voltage is 5 V, they can be interfaced; however, the fan-out of the CMOS is limited to two TTL gates.
- A 5 V Zener diode must be placed across the inputs of the TTL gates in order to protect them from the higher output voltages of the CMOS gates.
- The two series cannot be interfaced without the use of special interface buffers designed for that purpose, such as the open-collector buffers.
12. What is the static charge that can be stored by your body as you walk across a carpet?
- 300 volts
- 3,000 volts
- 30,000 volts
- Over 30,000 volts
13. Which of the following logic families has the highest noise margin?
- TTL
- LS TTL
- CMOS
- HCMOS
14. A "floating" TTL input may be defined as:
- unused input that is tied to Vcc through a 1 k resistor.
- unused input that is tied to used inputs.
- unused input that is tied to the ground.
- unused input that is not connected.
15. Which of the logic families listed below allows the highest operating frequency?
- 74AS
- ECL
- HCMOS
- 54S
16. Whenever a totem-pole TTL output goes from LOW to HIGH, a high-amplitude current spike is drawn from the Vcc supply. How is this effect corrected to a digital circuit?
- By connecting a radio-frequency capacitor from Vcc to ground.
- By using a switching power supply
- By connecting a capacitor from Vout to ground
- By connecting a large resistor from Vcc to Vout
17. What is the increase in switching speed between 74LS series TTL and 74HC/HCT (High-Speed CMOS)?
- 5
- 10
- 50
- 100
18. A logic signal experiences a delay in going through a circuit. The two propagation delay times are defined as:
- tPLH and tPHL.
- tDLH and tDHL.
- tHPL and tlph.
- tLDH and tHDL.
19. What does ECL stand for?
- It stands for electron-coupled logic; all of the devices used within the gates are N-type transistors.
- It stands for emitter-coupled logic; all of the inputs are coupled into the device through the emitters of the input transistors.
- It stands for emitter-coupled logic; all of the emitters of the input transistors are connected together and each transistor functions as an emitter follower.
- It stands for energy-coupled logic; the input energy is amplified by the input transistors and allows the device to deliver higher output currents.
20. What is unique about TTL devices such as the 74S00?
- The gate transistors are silicon (S), and the gates therefore have lower values of leakage current.
- The S denotes the fact that a single gate is present in the IC rather than the usual package of 2–6 gates.
- The S denotes a slow version of the device, which is a consequence of its higher power rating.
- The devices use Schottky transistors and diodes to prevent them from going into saturation; this results in faster turn on and turn off times, which translates into higher frequency operation.