# ADC0801 Datasheet - Page 13

Download or read online National Semiconductor ADC0801 8-Bit Microprocessor Compatible A/D Converters pdf datasheet.

Also see for ADC0801: Datasheet #2 (41 pages)

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Functional Description

1 0 UNDERSTANDING A D ERROR SPECS

A perfect A D transfer characteristic (staircase waveform) is

shown in Figure 1a The horizontal scale is analog input

voltage and the particular points labeled are in steps of 1

LSB (19 53 mV with 2 5V tied to the V

2 pin) The digital

REF

output codes that correspond to these inputs are shown as

D

1 D and D

1 For the perfect A D not only will center-

b

a

value (A

1 A A

1

) analog inputs produce the cor-

b

a

rect output ditigal codes but also each riser (the transitions

between adjacent output codes) will be located

away from each center-value As shown the risers are ideal

and have no width Correct digital output codes will be pro-

vided for a range of analog input voltages that extend

LSB from the ideal center-values Each tread (the range of

analog input voltage that provides the same digital output

code) is therefore 1 LSB wide

Figure 1b shows a worst case error plot for the ADC0801

All center-valued inputs are guaranteed to produce the cor-

rect output codes and the adjacent risers are guaranteed to

be no closer to the center-value points than

Transfer Function

Transfer Function

Transfer Function

FIGURE 1 Clarifying the Error Specs of an A D Converter

other words if we apply an analog input equal to the center-

LSB we guarantee that the A D will produce the

value

g

correct digital code The maximum range of the position of

the code transition is indicated by the horizontal arrow and it

is guaranteed to be no more than

The error curve of Figure 1c shows a worst case error plot

for the ADC0802 Here we guarantee that if we apply an

analog input equal to the LSB analog voltage center-value

the A D will produce the correct digital code

Next to each transfer function is shown the corresponding

LSB

g

error plot Many people may be more familiar with error plots

than transfer functions The analog input voltage to the A D

is provided by either a linear ramp or by the discrete output

g

steps of a high resolution DAC Notice that the error is con-

tinuously displayed and includes the quantization uncertain-

ty of the A D For example the error at point 1 of Figure 1a

is

LSB because the digital code appeared

a

advance of the center-value of the tread The error plots

always have a constant negative slope and the abrupt up-

side steps are always 1 LSB in magnitude

LSB In

g

a) Accuracy

0 LSB A Perfect A D

e

g

b) Accuracy

LSB

e

g

c) Accuracy

LSB

e

g

13

LSB

LSB in

Error Plot

Error Plot

Error Plot

TL H 5671 – 12

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