AD8651/AD8652

Rev. C | Page 17 of 20

1µF

3

2

U1

IN

2.7nF

33Ω

5V

1kΩ

10kΩ

10kΩ

1kΩ

AD7685

0V TO 5V

+

–

AD865x

2V p-p

47pF

600Ω

+3.5V

–1.5V

+

–

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.

http://www.analog.com/Analog_Root/productPage/productHome/0%2C21

21%2CAD7685%2C00.html

INPUT RANGE = 0V TO 5V

FREQUENCY (kHz)

0

–160

–100

–120

–140

–80

–60

–40

–20

0

10

20

30 40

50

60

70

80

90 100 110 120

Figure 60. Frequency Response of AD865x Driving a 16-Bit ADC