Datasheet

AD8651/AD8652
Rev. C | Page 17 of 20
1µF
3
2
U1
IN
2.7nF
33Ω
V
CC
5
V
1kΩ
10kΩ
10kΩ
1kΩ
AD7685
V
IN
0V TO 5V
f
IN
= 45kHz
03301-060
+
–
AD865x
V
+
V
–
V
IN
2V p-p
47pF
600Ω
V
OUT
+3.5V
–1.5V
03301-058
+
–
AD865x
Figure 59. THD + N Test Circuit
Figure 61. AD865x Driving a 16-Bit ADC
Driving a 16-Bit ADC
The AD865x family is an excellent choice for driving high
speed, high precision ADCs. The driver amplifier for this type
of application needs low THD + N as well as quick settling time.
Figure 61 shows a complete single-supply data acquisition
solution. The AD865x family drives the AD7685, a 250 kSPS,
16-bit data converter.
1
Table 6. Data Acquisition Solution of Figure 60
Parameter Reading (dB)
THD + N 105.2
SFDR 106.6
2nd Harmonics 107.7
3rd Harmonics 113.6
The AD865x is configured in an inverting gain of 1 with a 5 V
single supply. Input of 45 kHz is applied, and the ADC samples
at 250 kSPS. The results of this solution are listed in
Table 6.
The advantage of this circuit is that the amplifier and ADC can
be powered with the same power supply. For the case of
a noninverting gain of 1, the input common-mode voltage
encompasses both supplies.
1
For more information about the AD7685 data converter, go to
http://www.analog.com/Analog_Root/productPage/productHome/0%2C21
21%2CAD7685%2C00.html
f
SAMPLE
= 250kSPS
f
IN
= 45kHz
INPUT RANGE = 0V TO 5V
FREQUENCY (kHz)
AMPLITUDE (dB of Full Scale)
0
–160
–100
–120
–140
–80
–60
–40
–20
0
10 20 30 40 50 60 70 80 90 100 110 120
03301-059
Figure 60. Frequency Response of AD865x Driving a 16-Bit ADC