Philips Semiconductors Linear Products

Product specification

ADC0820

8-Bit, high-speed,

µP-compatible A/D converter with

track/hold function

August 31, 1994

580

therefore not necessary to filter out these transients by putting an

within 600ns is used to drive the input. The NE530 is a suitable op

amp for driving the input of the ADC0820.

Inherent Sample-Hold

Another benefit of the ADC0820’s input mechanism is its ability to

measure a variety of high-speed signals without the help of an

external sample-and-hold. In a conventional SAR type converter,

regardless of its speed, the input must remain at least 1/2LSB

stable throughout the conversion process if full accuracy is to be

maintained. Consequently, for many high-speed signals, this signal

must be externally sampled, and held stationary during the

conversion.

Sampled data comparators, by nature of their input switching,

already accomplish this function to a large degree (Section 1.2).

Although the conversion time for the ADC0820 is 1.5

µs, the time

WR is Low. Even though the two flashes are not done

simultaneously, the analog signal is measured at one instant. The

due to internal logic propagation delay) will be the measured value.

Input signals with slew rates typically below 100mV/

µs can be

converted without error. However, because of the input time

constants, and charge injection through the opened comparator

input switches, faster signals may cause errors. Still, the ADC0820’s

loss in accuracy for a given increase in signal slope is far less than

what would be witnessed in a conventional successive

approximation device. An SAR type converter with a conversion

time as fast as 1

µs would still not be able to measure a 5V, 1kHz

sine wave without the aid of an external sample-and-hold. The

ADC0820, with no such help, can typically measure 5V, 7kHz

waveforms.

+5V

0.1

µF 47µF

VREF

VIN

VDD

VDD

VIN

VREF(+)

VREF(–)

GND

MODE

INT

RD

DB7

DB0

RDY

CS

Figure 11. 8-Bit Resolution Configuration

–

+

(+4VCC, 3kHz MAX)

+5V

25k

12k

+5V

0.1

µF

47

µF

+5V

VIN

VREF(+)

VDD

VREF(–)

GND

MODE

DB7

DB0

INT

RD

WR

CS

40k

27k

VIN

Figure 12. Telecom A/D Converter