ADC0804LCWMXSLASHNOPB datasheet(16/56 Pages) TI1

16 / 56 page

ADC0801, ADC0802, ADC0803, ADC0804, ADC0805

SNOSBI1C – NOVEMBER 2009 – REVISED JUNE 2015

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Application Information (continued)

Figure 23. Basic ADC Tester

For a higher speed test system, or to obtain plotted data, a digital-to-analog converter is needed for the test set-

up. An accurate 10-bit DAC can serve as the precision voltage source for the ADC. Errors of the ADC under test

can be expressed as either analog voltages or differences in 2 digital words.

A basic ADC tester that uses a DAC and provides the error as an analog output voltage is shown in Figure 35.

The 2 op amps can be eliminated if a lab DVM with a numerical subtraction feature is available to read the

difference voltage, "A–C", directly. The analog input voltage can be supplied by a low frequency ramp generator

and an X-Y plotter can be used to provide analog error (Y axis) versus analog input (X axis).

For operation with a microprocessor or a computer-based test system, it is more convenient to present the errors

digitally. This can be done with the circuit of Figure 25, where the output code transitions can be detected as the

10-bit DAC is incremented. This provides 1

⁄4 LSB steps for the 8-bit ADC 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 ADC under test results. For acceptance testing, the plot is not necessary and the testing speed

can be increased by establishing internal limits on the allowed error for each code.

9.1.2 Microprocessor Interfacing

To discuss the interface with 8080A and 6800 microprocessors, a common sample subroutine structure is used.

The microprocessor starts the ADC, reads and stores the results of 16 successive conversions, then returns to

the user’s program. The 16 data bytes are stored in 16 successive memory locations. All Data and Addresses

will be given in hexadecimal form. Software and hardware details are provided separately for each type of

microprocessor.

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