A low speed ramp generator can also be used to sweep the

analog input voltage and the LED outputs will provide a bi-

nary counting sequence from zero to full-scale

The techniques described so far are suitable for an engi-

neering evaluation or a quick check on performance For a

higher speed test system or to obtain plotted data a digital-

to-analog converter is needed for the test set-up An accu-

rate 10-bit DAC can serve as the precision voltage source

for the AD Errors of the AD under test can be provided as

either analog voltages or differences in two digital words

A basic AD tester which uses a DAC and provides the error

as an analog output voltage is shown in

Figure 6 The2op

amps can be eliminated if a lab DVM with a numerical sub-

traction feature is available to directly readout the difference

voltage ‘‘A – C’’

For operation with a microprocessor or a computer-based

test system it is more convenient to present the errors digi-

tally This can be done with the circuit of

Figure 7 where the

output code transitions can be detected as the 10-bit DAC is

incremented This provides

LSB steps for the 8-bit AD

under test If the results of this test are automatically plotted

with the analog input on the X axis and the error (in LSB’s)

as the Y axis a useful transfer function of the AD under

test results For acceptance testing the plot is not neces-

sary and the testing speed can be increased by establishing

internal limits on the allowed error for each code

TLH5670 – 16

FIGURE 6 AD Tester with Analog Error Output

TLH5670 – 17

FIGURE 7 Basic ‘‘Digital’’ AD Tester

Connection Diagram

Dual-In-Line Package

TLH5670 – 9

Top View

Order Number ADC0800PD

or ADC0800PCD

See NS Package Number D18A

9