Electronic Engineers Notebook

High speed digital design


Transmission Lines

Logic Families

Metastability

Resistor Colour Code


Transmission Lines

Rule of thumb: "Transmission line theory has to be applied when the propagation delay of the line is greater than half the signal rise time." Depending on the application, it may be necessary for even shorter lines than this.

Impedance and Propagation delay

Typical values

 

L (nH/cm)

C (pF/cm)

Z ( W )

t (ns/m)

Isolated wire

20

0.06

600

~4

Space

m o

e o

370

3.3

Twisted pair cable

5-10

0.5-1

80-120

5

Flat cable

5-10

0.5-1

80-120

5

Wire on PC board

5-10

0.5-1.5

70-100

~5

Coax cable

2.5

1

50

5

Bus line

5-10

10-30

20-40

10-20

m o = p 4e-7 H/m e o = 8.854e-12 F/m

Two wires (Twisted Pair)

Two wires - Twisted Pair

Twisted pair impedance

Twisted pair capacitance and inductance

Wire over ground plane

Wire over ground

Wire over ground impedance

Wire over ground capacitance and inductance

Coax

Coax cable

Coax cable impedance

Coax cable capacitance and inductance

Microstrip

Microstrip

Microstrip capacitance and inductance

Microstrip impedance and delay

Stripline (Triplate)

Stripline - Triplate

h1 = h2:

Stripline impedance and delay

Usually h1 ¹ h2. If Z(k) is the symmetrical stripline impedance formula then an approximation is:

Non-symmetric approximation

Traces side by side

PCB traces

PCB traces impedance and delay

Flat Parallel Conductors

Flat parallel conductors

Flat parallel conductors impedance

Logic Families

5V

Family

Typical delay ns

Slew rate V/ns

F

4

1.3

ABT

2.7

1.0

HC

13

0.9

AHC

5.5

0.8

AC

5

2

ALS

6

1

3.3V

Family

Typical delay ns

Slew rate V/ns

LVT

2.4

1.2

ALVC

2.0

1.3

LVC

4.5

0.9

AHC

8.3

0.5

LV

10

0.7

Metastability

Metastability MTBF

t = time available for the flip flop to decide between high and low
f in = data rate at D input
f clk = clock frequency

 

F (ns -1 )

T o (s)

74

0.74

2.9e-4

74LS

0.72

4.8e-3

74S

0.36

1.3e-9

74ALS

1.02

8.8e-6

74AS

4.03

1.4e3

74F

9.2

1.9e8

74BCT

1.51

1.14e-6

74ABT

3.61

0.033

74HC

0.55

1.48e-6

74AHC

1.41

2.9e-4

74AC

2.8

1.1e-4

74LV

0.6

1.38e-5

74LVC

4.4

4.008

74ALVC

4.6

1.047

74LVT

2.13

1.52e-4

Resistor Colour Code

 

Digit

Multiplier

Tolerance

Black

0

1

 

Brown

1

10

1%

Red

2

100

2%

Orange

3

1000

 

Yellow

4

10,000

 

Green

5

100,000

 

Blue

6

1,000,000

 

Purple

7

   

Grey

8

   

White

9

   

Gold

 

0.1

5%

Silver

 

0.01

10%


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Last updated July 16, 2000
© 2000 Michael Wells