AD7821 Analog Devices, AD7821 Datasheet - Page 12

• Manufacturer Part Number: AD7821
• Manufacturer: Analog Devices

Specifications of AD7821

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 1MSPS
• Interface: Par
• Analog Input Type: SE-Bip,SE-Uni
• Ain Range: Bip (Vref),Uni (Vref)
• Adc Architecture: Pipelined
• Pkg Type: DIP,LCC,SOIC

AD7821
APPLYING THE AD7821
The AD7821 is specified for a unipolar input range of 0 V to +5 V
and a bipolar input range of –2.5 V to +2.5 V. The V
V
below. See the Typical Performance Characteristics section for
operation with unspecified input voltage ranges.
UNIPOLAR OPERATION
Figure 18 gives the configuration and reference voltages required
for 0 V to +5 V operation. The nominal transfer characteristic
for this input range is shown in Figure 19. The output code is
Natural Binary with 1 LSB = (5/256) V = 19.5 mV.
Figure 19. Nominal Transfer Characteristic for Unipolar
(0 V to +5 V) Operation
REF
(+) voltages required for these input ranges are outlined
Figure 18. Unipolar/Bipolar Operation
REF
(–) and
–12–
BIPOLAR OPERATION
Figure 18 gives the configuration and reference voltages required
for –2.5 V to +2.5 V operation. The nominal transfer characteris-
tic for this input range is shown in Figure 20. The output code is
Offset Binary with 1 LSB = ([+2.5 – (–2.5)]/256) V = 19.5 mV.
16-CHANNEL TELECOM A/D CONVERTER
The fast sampling rate (1 MHz) and bipolar operation of the
AD7821 makes it useful in telecom applications for sampling a
number of input channels using a multiplexer. Figure 21 shows
a circuit for such an application.
The maximum signal frequency required for acceptable quality
in telecom applications is 3 kHz. The circuit given in Figure 21
permits each of the 16-input channels to be sampled at a rate of
16 kHz maximum. The sampling rate takes into account such
multiplexer parameters as t
circuit also eases the problem of the antialiasing filter design by
sampling at a rate much greater than that required by the
Nyquist criterion.
Figure 20. Nominal Transfer Characteristic for Bipolar
(–2.5 V to +2.5 V) Operation
ON
, settling time, and so on. The
REV. B