AD7568

–8–

UNIPOLAR BINARY OPERATION

(2-Quadrant Multiplication)

Figure 15 shows the standard unipolar binary connection dia-

signal, the circuit performs 2-quadrant multiplication. Resistors

R1 and R2 allow the user to adjust the DAC gain error. Offset

can be removed by adjusting the output amplifier offset voltage.

A1 should be chosen to suit the application. For example, the

AD OP07 or OP177 are ideal for very low bandwidth applica-

tions while the AD843 and AD845 offer very fast settling time

in wide bandwidth applications. Appropriate multiple versions

of these amplifiers can be used with the AD7568 to reduce

board space requirements.

The code table for Figure 15 is shown in Table III.

DAC A

A1

I

A

OUT1

I

A

OUT2

AD7568

V

OUT

R

A

FB

V

A

REF

V

IN

NOTES

1. ONLY ONE DAC IS SHOWN FOR CLARITY.

2. DIGITAL INPUT CONNECTIONS ARE OMITTED.

3. C1 PHASE COMPENSATION (5–15pF) MAY BE

REQUIRED WHEN USING HIGH SPEED AMPLIFIER, A1.

R2 10

Ω

R1 20

Ω

SIGNAL

GND

A1: OP-177

ADOP-07

AD711

AD843

AD845

C1

Figure 15. Unipolar Binary Operation

Table III. Unipolar Binary Code Table

Digital Input

Analog Output

MSB………LSB

1111 1111 1111

1000 0000 0001

1000 0000 0000

0111 1111 1111

0000 0000 0001

0000 0000 0000

NOTE

Nominal LSB size for the circuit of Figure 15 is given by:

BIPOLAR OPERATION

(4-Quadrant Multiplication)

Figure 16 shows the standard connection diagram for bipolar

operation of any one of the DACs in the AD7568. The coding is

the circuit performs 4-quadrant multiplication. To maintain the

gain error specifications, resistors R3, R4 and R5 should be ra-

tio matched to 0.01%.

DAC A

A1

I

A

OUT1

I

A

OUT2

AD7568

V

OUT

R

A

FB

V

A

REF

V

IN

NOTES

1. ONLY ONE DAC IS SHOWN FOR CLARITY.

2. DIGITAL INPUT CONNECTIONS ARE OMITTED.

3. C1 PHASE COMPENSATION (5–15pF) MAY BE

REQUIRED WHEN USING HIGH SPEED AMPLIFIER, A1.

R2 10

Ω

R1 20

Ω

SIGNAL

GND

C1

A2

R3

10k

Ω

R5

20k

Ω

20k

Ω

R4

Figure 16. Bipolar Operation (4-Quadrant Multiplication)

Table IV. Bipolar (Offset Binary) Code Table

Digital Input

Analog Output

MSB . . . . . LSB

1111 1111 1111

1000 0000 0001

1000 0000 0000

0111 1111 1111

0000 0000 0001

0000 0000 0000

NOTE

Nominal LSB size for the circuit of Figure 16 is given by:

SINGLE SUPPLY CIRCUITS

The AD7568 operates from a single +5 V supply, and this

makes it ideal for single supply systems. When operating in such

a system, it is not possible to use the standard circuits of Figures

two alternatives. One of these continues to operate the DAC as

a current-mode device, while the other uses the voltage switch-

ing mode.

DAC A

A1

I

A

OUT1

I

A

OUT2

AD7568

V

BIAS

V

OUT

R

A

FB

V

A

REF

V

IN

NOTES

1. ONLY ONE DAC IS SHOWN FOR CLARITY.

2. DIGITAL INPUT CONNECTIONS ARE OMITTED.

3. C1 PHASE COMPENSATION (5–15pF) MAY BE

REQUIRED WHEN USING HIGH SPEED AMPLIFIER, A1.

Figure 17. Single Supply Current-Mode Operation

REV. C