AD7869JRZ Analog Devices Inc, AD7869JRZ Datasheet - Page 10

• Manufacturer Part Number: AD7869JRZ
• Description: IC I/O PORT 14BIT ANLG 28SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD7869JRZ

• Applications: Analog I/O
• Interface: TTL/CMOS
• Voltage - Supply: 4.75 V ~ 5.25 V
• Package / Case: 28-SOIC (7.5mm Width)
• Mounting Type: Surface Mount
• Ic Function: A/D Converter (A-D)
• Supply Voltage Range: ± 4.75V To ± 5.25V
• Operating Temperature Range: 0°C To +70°C
• Digital Ic Case Style: SOIC
• No. Of Pins: 28
• Msl: MSL 3 - 168 Hours
• Converter Type: ADC/DAC
• Resolution: 14b
• Number Of Dac's: Single
• Data Rate: 0.083MSPS
• Digital Interface Type: Serial
• Pin Count: 28
• Package Type: SOIC W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

AD7869
The digitizer sampling is synchronized with the DAC update
rate to ease FFT calculations. The digitizer samples the DAC
output after the output has settled to its new value. Therefore, if
the digitizer were to directly sample the output, it would effec-
tively be sampling a dc value each time. As a result, the dynamic
performance of the DAC would not be measured correctly. Us-
ing the digitizer directly on the DAC output would give better
results than the actual performance of the DAC. Using a filter
between the DAC and the digitizer means that the digitizer
samples a continuously moving signal, and the true dynamic
performance of the AD7869 DAC output is measured.
Figure 12 shows a typical 2048 point Fast Fourier Transform
plot for the AD7869 DAC with an update rate of 83 kHz and an
output frequency of 1 kHz. The SNR obtained from the graph is
82 dBs.
Some applications will require improved performance versus fre-
quency from the AD7869 DAC. In these applications, a simple
sample-and-hold circuit such as that outlined in Figure 13 will
extend the very good performance of the DAC to 20 kHz. Other
applications will already have an inherent sample-and-hold
function following the AD7869 DAC output. An example of
this type of application is driving a switched capacitor filter
where the updating of the DAC is synchronized with the
switched capacitor filter. This inherent sample-and-hold func-
tion also extends the frequency range performance.
LDAC
Figure 13. DAC Sample-and-Hold Circuit
AD7869*
LDAC
Figure 12. DAC FFT Plot
V
ONE SHOT
OUT
DELAY
1 s
Q
2k2
R1
*ADDITIONAL PINS OMITTED FOR CLARITY
S1
ADG201HS
IN1
D1
2k2
R2
330pF
C9
AD711
–10–
Performance versus Frequency
The typical performance plots of Figures 14 and 15 show the
AD7869 DAC performance over a wide range of input frequen-
cies at an update rate of 83 kHz. The plot of Figure 14 is with-
out a sample-and-hold on the DAC output while the plot of
Figure 15 is generated with a sample-and-hold on the output.
Figure 15. DAC Performance vs. Frequency (Sample-and-
Hold)
Figure 14. DAC Performance vs. Frequency (No
Sample-and-Hold)
REV. B