AD974AR Analog Devices Inc, AD974AR Datasheet - Page 17

• Manufacturer Part Number: AD974AR
• Description: A/D Converter (A-D) IC
• Manufacturer: Analog Devices Inc
• Type: Data Acquisition System (DAS)r

Specifications of AD974AR

• Package/case: 28-SOIC
• Features: 4?Ch., 200kSPS Data Acquisition System
• Interface Type: Serial
• Number Of Bits: 16
• Number Of Channels: 4
• Mounting Type: Surface Mount
• Rohs Status: RoHS non-compliant
• Resolution (bits): 16 b
• Sampling Rate (per Second): 200k
• Data Interface: Serial
• Voltage Supply Source: Analog and Digital
• Voltage - Supply: 5V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: EVAL-AD974CB - BOARD EVAL FOR AD974
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

DC CODE UNCERTAINTY
Ideally, a fixed dc input should result in the same output code
for repetitive conversions; however, as a consequence of un-
avoidable circuit noise within the wideband circuits of the ADC,
a range of output codes may occur for a given input voltage.
Thus, when a dc signal is applied to the AD974 input, and
10,000 conversions are recorded, the result will be a distribution
of codes as shown in Figure 21. This histogram shows a bell
shaped curve consistent with the Gaussian nature of thermal
noise. The histogram is approximately seven codes wide. The
standard deviation of this Gaussian distribution results in a code
transition noise of 1 LSB rms.
POWER-DOWN FEATURE
The AD974 has analog and reference power-down capability
through the PWRD pin. When the PWRD pin is taken high,
the power consumption drops from a maximum value of
100 mW to a typical value of 50 W. When in the power-
down mode the previous conversion results are still available in
the internal registers and can be read out providing it has not
already been shifted out.
REV. A
Figure 21. Histogram of 10,000 Conversions of a DC Input
110
105
100
95
90
85
80
4000
3500
3000
2500
2000
1500
1000
–75
500
Figure 20. AC Parameters vs. Temperature
0
–50
–3
–25
–2
0
TEMPERATURE – C
SNRD
–1
SFDR
THD
25
0
50
1
75
2
100
3
125
4
150
–80
–85
–90
–95
–100
–105
–110
–17–
When used with an external reference, connected to the REF
pin and a 2.2 F capacitor, connected to the CAP pin, the
power-up recovery time is typically 1 ms. This typical value of
1 ms for recovery time depends on how much charge has de-
cayed from the external 2.2 F capacitor on the CAP pin and
assumes that it has decayed to zero. The 1 ms recovery time has
been specified such that settling to 16 bits has been achieved.
When used with the internal reference, the dominant time con-
stant for power-up recovery is determined by the external ca-
pacitor on the REF pin and the internal 4K impedance seen at
that pin. An external 2.2 F capacitor is recommended for the
REF pin.
CROSSTALK
The crosstalk between adjacent channels, nonadjacent channels
and worst-case adjacent channels is shown in Figures 22 to 24.
The worst-case crosstalk occurs between channels 1 and 2.
Figure 23. Adjacent Channel Crosstalk, Worst Pair
(8192 Point FFT; AIN 2 = 1.02 kHz, –0.1 dB; AIN 1 = AGND)
–100
–110
–120
–130
Figure 22. Crosstalk vs. Input Frequency (kHz)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–105
–110
–115
–80
–85
–90
–95
0
1
1
2
ACTIVE CHANNEL INPUT FREQUENCY – kHz
4
10
6
ADJACENT CHANNELS,
FREQUENCY – kHz
WORST PAIR
8
10
100
12
14
NONADJACENT
1000
CHANNELS
16
AD974
18
10000
20