AD8651 Analog Devices, AD8651 Datasheet - Page 17

• Manufacturer Part Number: AD8651
• Description: 50 MHz, Precision, Low Distortion, Low Noise CMOS Amplifiers
• Manufacturer: Analog Devices

Specifications of AD8651

• -3db Bandwidth: 50MHz
• Slew Rate: 41V/µs
• Vos: 100µV
• Ib: 1pA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 4.5nV/rtHz
• Vcc-vee: 2.7V to 5.5V
• Isy Per Amplifier: 9mA
• Packages: SOIC,SOP

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.
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
Figure 60. Frequency Response of AD865x Driving a 16-Bit ADC
–100
–120
–140
–160
–20
–40
–60
–80
2V p-p
0
0
V
IN
10
20
+
–
AD865x
Figure 59. THD + N Test Circuit
+3.5V
–1.5V
1
30 40
FREQUENCY (kHz)
50
60
70
600Ω
f
f
INPUT RANGE = 0V TO 5V
SAMPLE
IN
80
= 45kHz
90
= 250kSPS
47pF
100 110 120
V
OUT
Rev. C | Page 17 of 20
Table 6. Data Acquisition Solution of Figure 60
Parameter
THD + N
SFDR
2nd Harmonics
3rd Harmonics
1µF
f
IN
0V TO 5V
10kΩ
10kΩ
= 45kHz
V
IN
Figure 61. AD865x Driving a 16-Bit ADC
1kΩ
3
2
+
–
AD865x
5V
V
V
1kΩ
+
U1
–
Reading (dB)
105.2
106.6
107.7
113.6
AD8651/AD8652
33Ω
2.7nF
IN
V
AD7685
CC