Data Sheet
AD7938/AD7939
Rev. C | Page 11 of 36
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
SUPPLY RIPPLE FREQUENCY (kHz)
P
S
RR
(
d
B)
–60
–70
–80
–90
–110
–100
–120
10
210
610
410
810
1010
03
71
5-
00
7
100mV p-p SINE WAVE ON VDD AND/OR VDRIVE
NO DECOUPLING
DIFFERENTIAL/SINGLE-ENDED MODE
INT REF
EXT REF
Figure 4. PSRR vs. Supply Ripple Frequency Without Supply Decoupling
NOISE FREQUENCY (kHz)
IS
OLA
T
ION
(
d
B
)
–70
–75
–90
–85
–80
–95
0
100
400
200
300
600
500
800
700
03
71
5-
02
1
INTERNAL/EXTERNAL REFERENCE
VDD =5V
Figure 5. AD7938 Channel-to-Channel Isolation
FREQUENCY (kHz)
S
INAD
(
d
B
)
80
70
60
50
40
30
20
0
100
400
200
300
600
500
1000
700
800
900
03
71
5-
00
8
FSAMPLE =1.5MSPS
RANGE = 0 TO VREF
DIFFERENTIAL MODE
VDD =5V
VDD =3V
Figure 6. AD7938 SINAD vs. Analog Input Frequency
for Various Supply Voltages
FREQUENCY (kHz)
0
–10
–20
–50
–40
–30
–90
–100
–80
–70
–60
–110
0
100
200
300
400
500
600
700
03
71
5-
0
09
4096 POINT FFT
VDD =5V
FSAMPLE =1.5MSPS
FIN = 49.62kHz
SINAD = 70.94dB
THD = –90.09dB
DIFFERENTIAL MODE
AM
P
L
IT
U
D
E
(
d
B)
Figure 7. AD7938 FFT @ VDD = 5 V
CODE
DNL
E
RRO
R
(
L
S
B
)
1.0
0.8
0.6
0.4
0.2
–0.2
0
–0.8
–0.6
–0.4
–1.0
0
500
2000
1000
1500
3000
2500
4000
3500
03
71
5-
01
0
VDD =5V
DIFFERENTIAL MODE
Figure 8. AD7938 Typical DNL @ VDD = 5 V
CODE
INL
E
RRO
R
(L
S
B)
1.0
0.8
0.6
0.4
0.2
–0.2
0
–0.8
–0.6
–0.4
–1.0
0
500
2000
1000
1500
3000
2500
4000
3500
03
71
5-
01
1
VDD =5V
DIFFERENTIAL MODE
Figure 9. AD7938 Typical INL @ VDD = 5 V