8-Bit, Microprocessor-Compatible, A/D
The ADC080X family are CMOS 8-Bit, successiveapproximation A/D converters which use a modified potentiometric ladder and are designed to operate with the
8080A control bus via three-state outputs. These converters
appear to the processor as memory locations or I/O ports,
and hence no interfacing logic is required.
The differential analog voltage input has good commonmode-rejection and permits offsetting the analog zero-inputvoltage value. In addition, the voltage reference input can be adjusted to allow encoding any smaller analog voltage span
to the full 8 bits of resolution.
Typical Application Schematic
• 80C48 and 80C80/85 Bus Compatible - No Interfacing
• Conversion Time . . . . . . . . . . . . . . . . . . . . . . . . . . 1kΩ). If input bypass capacitors are necessary for noise filtering and high source resistance is desirable to
minimize capacitor size, the effects of the voltage drop across this input resistance, due to the average value of the input current, can be compensated by a full scale adjustment while the given source resistor and input bypass capacitor are both in place. This is possible because the average value of the
input current is a precise linear function of the differential input voltage at a constant conversion rate.
( 5 × 10 ) ( 640 × 10 )
V PEAK = --------------------------------------------------------- ≅ 1.9V . ( 6.28 ) ( 60 ) ( 4.5 )
The allowed range of analog input voltage usually places
more severe restrictions on input common-mode voltage
levels than this.
An analog input voltage with a reduced span and a relatively large zero offset can be easily handled by making use of the differential input (see Reference Voltage Span Adjust).
Analog Input Current
The internal switching action causes displacement currents to flow at the analog inputs. The voltage...