AD7845

REV. B

–7–

UNIPOLAR BINARY OPERATION

Figure 13 shows the AD7845 connected for unipolar binary

2-quadrant multiplication. The code table for Figure 13 is given

in Table I.

Figure 13. Unipolar Binary Operation

Table I. Unipolar Binary Code Table for AD7845

Binary Number In

DAC Register

MSB

LSB

1111

1111

1111

4095

4096









1000

0000

0000

2048

4096









0000

0000

0001

1

4096









0000

0000

0000

0 V

OFFSET AND GAIN ADJUSTMENT FOR FIGURE 13

Zero Offset Adjustment

1. Load DAC with all 0s.

Gain Adjustment

1. Load DAC with all 1s.

4095

4096

.

In fixed reference applications, full scale can also be adjusted by

omitting R1 and R2 and trimming the reference voltage magni-

tude. For high temperature applications, resistors and potenti-

ometers should have a low temperature coefficient.

BIPOLAR OPERATION

(4-QUADRANT MULTIPLICATION)

The recommended circuit for bipolar operation is shown in

Figure 14. Offset binary coding is used.

The offset specification of this circuit is determined by the

offset error of the device. Gain error may be adjusted by varying

the ratio of R1 and R2.

To use this circuit without trimming and keep within the gain

error specifications, resistors R1 and R2 should be ratio

matched to 0.01%.

The code table for Figure 14 is given in Table II.

Figure 14. Bipolar Offset Binary Operation

Table II. Bipolar Code Table for Offset Binary Circuit of

Figure 14

Binary Number In

DAC Register

MSB

LSB

1111

1111

1111

2047

2048









1000

0000

0001

1

2048









1000

0000

0000

0 V

0111

1111

1111

1

2048









0000

0000

0000

2048

2048





