Logic Gates

1
Logic Gates

• Basic functions
• AND, OR, NAND, NOR, Inverter
• Truth table
• Performance
• Static transfer function (output versus input)
• Dynamic switching time and delay
• Fan out driving capability

x y ----- 0 1 1 0
2
Types of Logic Gates

• TTL
• Low power Schottky
• ECL
• CMOS

3
CMOS Inverter

• Single stage
• Transfer function
• Rise time
• Power consumption versus frequency
• Delay
• Cascading
• Ring oscillator
• http//jas.eng.buffalo.edu/education/mos/inverter/
  index2.html
• http//www.ecdl.hut.fi/education/137/DIGITAL/CMOSi
  nv.PDF

4
CMOS Inverter
DC Current
DC Power Supply Function Generator 2.5 V pp
1.25 V offset
DC Voltage Oscilloscope
5

• Pin 14 DC 5 V
• Pin 7 Gnd
• Pin 6 Input
• Pins 13 and 8 connected together - Output

6
Single Stage

• DC transfer function
• Manual measurement with power supply

7
Single Stage

• Automatic measurement
• Function generator
• 0 to 5 V triangular wave, 100 Hz
• 2.5 V pp, 1.25 V offset
• Oscilloscope
• Input waveform
• Output waveform
• Data acquisition
• Plot Vout vs. Vin

8
Single Stage

• Pulse transition time
• 10-90 rise time
• 90-10 fall or decay time
• Power versus switching rate
• Capacitor charge storage
• http//bwrc.eecs.berkeley.edu/Classes/ICDesign/ee1
  41_s04/Lectures/Lecture4-Inverter.pdf

9
Single Stage

• Power Consumption
• Function generator
• 0-5 V pulses (2.5 V pp, 1.25 V offset)
• DC current meter in series
• P I V
• Scan frequency
• Plot power vs. frequency

10
Propagation Delay

• Difficult to measure with single stage
• Cascade 2 or 3 stages
• 50 input - 50 output
• delay

11
Ring Oscillator

• Cascade 3 stages
• Connect the output back to input.
• Relation between oscillation frequency, delay,
  and stage count

12
Logic Level Compatible Signal

• Schmidt trigger

http//hyperphysics.phy-astr.gsu.edu/hbase/electro
nic/schmitt.html
13
74LS00

• Low power Schottky
• NAND gate
• Connect both input ports to form an inverter.
• Switching characteristics
• Ring oscillator
• http//ocw.mit.edu/NR/rdonlyres/Electrical-Enginee
  ring-and-Computer-Science/6-111Spring2004/B0DB9F22
  -CE77-4C31-8D17-5697B2CAE308/0/lab1.pdf

14
74LS00
Fast!
15
Compare CMOS to Schottky

• Which is faster?
• Guess which consumes more power?

16
Other Inverters

• MOS
• BJT

17
Activities

• Build three CMOS inverters
• Measure DC transfer function
• Switching region with fine readings
• Measure rise and decay time
• Measure delay time
• Measure power consumption vs. frequency
• Connect all three inverters into a ring
  oscillator
• Frequency
• Waveform
• f vs delay

18
Critical Thinking

• Why does a faster computer consume more power?
• How to make a notebook computer battery run
  longer?