AD7767

Rev. C | Page 20 of 2

4

DRIVING THE AD7767

R1 and R2 set the attenuation ratio between the input range and

the desired input resistance, signal bandwidth, antialiasing, and

noise contribution. The ratio of R2 to R1 should be equal to the

ratio of REF to the peak-to-peak input voltage. For example, for

the ±10 V range with a 4 kΩ impedance, R2 = 1 kΩ and R1 = 4 kΩ.

The AD7767 must be driven with fully differential inputs. The

common-mode voltage of the differential inputs to the AD7767

device and therefore the limits on the differential inputs are set

has a 5 V supply (using ADR445, ADR435, or ADR425), the

common mode is at 2.5 V, meaning that the maximum inputs that

can be applied on the AD7767 differential inputs are a 5 V p-p

input around 2.5 V.

R3 and R4 set the common mode on the IN− input, and R5 and R6

set the common mode on the IN+ input of the ADC. The common

0V

2

0V

2

ADA4841-1

15

Ω

3.3nF

1k

Ω

ADA4841-1

15

Ω

3.3nF

1k

Ω

4

5

1

2

AD7767

2.2nF

2.2nF

*

ADR4xx

ADP3330-2.5

2.5V

2.5V TO 5V

REFERENCE

VOLTAGE

1k

Ω

1k

Ω

1k

Ω

1k

Ω

AIN+

AIN–

Figure 39. Maximum Differential Inputs to the AD7767

However, the AD7767 allows the user to apply a reference

voltage of up to 5 V. This provides the user with an increased

full-scale range, offering the user the option of using the

AD7767 with a greater LSB voltage. Figure 39 shows the

maximum inputs to the AD7767.

Figure 40. Driving the AD7767 from a Fully Differential Source

15

Ω

15

Ω

100µF

R1

100nF

100nF

2.5V

VOUT = 5V REF

5.2V

–0.2V

R4

R2

R6

Vin

R3

R5

AGND

AD7767

2.2nF

2.2nF

ADA4941

IN

FB

OUTP

OUTN

REF

Voffset1

Voffset2

ADR425

ADR445

ADP3330-2.5

LDO

DGND

0.1µF

0.1µF

DIFFERENTIAL SIGNAL SOURCE

An example of recommended driving circuitry that can be used

in conjunction with the AD7767/AD7767-1/AD7767-2 is shown in

Figure 40. Figure 40 shows how the ADA4841-1 device can be

used to drive an input to the AD7767/AD7767-1/AD7767-2

from a differential source. Each of the differential paths is

driven by an ADA4841-1 device.

SINGLE-ENDED SIGNAL SOURCE

For applications using a single-ended analog signal, either

bipolar or unipolar, the ADA4941-1 single-ended-to-differential

driver creates a fully differential input to the AD7767/AD7767-1/

AD7767-2. The schematic is shown in Figure 41.

Figure 41. Driving the AD7767 from a Single-Ended Source

Table 8. Resistor Values Required When Using the Differential to Single-Ended Circuit with ADA4941 (See Figure 41)

OUT+ (V)

OUT− (V)

R1 (kΩ)

R2 (kΩ)

R4 (kΩ)

R3 = R5 = R6 (kΩ)

+20, −20

2.5

2.203

−0.01, +4.96

5.01, 0.04

8.06

1

12.7

10

+10, −10

2.5

2.000

0.01, 4.99

4.99, 0.01

4.02

1

15

10

+5, −5

2.5

1.667

0.00, 5.00

5.00, 0.00

2

1

20

10