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AD7537LP-REEL

LC2MOS (8+4) Loading Dual 12-Bit DAC

Analog Devices 

Applications–AD7537

UNIPOLAR BINARY OPERATION

(2-QUADRANT MULTIPLICATION)

Figure 4 shows the circuit diagram for unipolar binary opera-

tion. With an ac input, the circuit performs 2-quadrant multipli-

cation. The code table for Figure 4 is given in Table II.

Operational amplifiers A1 and A2 can be in a single package

(AD644, AD712) or separate packages (AD544, AD711,

AD OP27). Capacitors C1 and C2 provide phase compensation

to help prevent overshoot and ringing when high-speed op amps

are used.

For zero offset adjustment, the appropriate DAC register is

loaded with all 0s and amplifier offset adjusted so that VOUTA or

VOUTB is 0 V. Full-scale trimming is accomplished by loading

the DAC register with all 1s and adjusting R1 (R3) so that

VOUTA (VOUTB) = –VIN (4095/4096). For high temperature op-

eration, resistors and potentiometers should have a low Tem-

perature Coefficient. In many applications, because of the

excellent Gain T.C. and Gain Error specifications of the

AD7537, Gain Error trimming is not necessary. In fixed refer-

ence applications, full scale can also be adjusted by omitting R1,

R2, R3, R4 and trimming the reference voltage magnitude.

BIPOLAR OPERATION

(4-QUADRANT MULTIPLICATION)

The recommended circuit diagram for bipolar operation is

shown in Figure 5. Offset binary coding is used.

With the appropriate DAC register loaded to 1000 0000 0000,

adjust R1 (R3) so that VOUTA (VOUTB) = 0 V. Alternatively, R1,

R2 (R3, R4) may be omitted and the ratios of R6, R7 (R9, 10)

varied for VOUTA (VOUTB) = 0 V. Full-scale trimming can be ac-

complished by adjusting the amplitude of VIN or by varying the

value of R5 (R8).

If R1, R2 (R3, R4) are not used, then resistors R5, R6, R7 (R8,

R9, R10) should be ratio matched to 0.01% to ensure gain error

performance to the data sheet specification. When operating

over a wide temperature range, it is important that the resistors

be of the same type so that their temperature coefficients match.

The code table for Figure 5 is given in Table III.

Figure 4. AD7537 Unipolar Binary Operation

Table II. Unipolar Binary Code Table for

Circuit of Figure 4

Binary Number in

DAC Register

MSB

LSB

Analog Output,

VOUTA or VOUTB

1111 1111 1111

−V

IN

⎛

⎝⎜

4095

4096

⎞

⎠⎟

1000 0000 0000

0000 0000 0001

0000 0000 0000

REV. A

−V IN

⎛

⎝⎜

2048

4096

⎞

⎠⎟

=

−

1

2

V

IN

−V

IN

⎛

⎝⎜

1

4096

⎞

⎠⎟

0V

Figure 5. Bipolar Operation (Offset Binary Coding)

Table III. Bipolar Code Table for Offset Binary

Circuit of Figure 5

Binary Number in

DAC Register

MSB

LSB

Analog Output,

VOUTA or VOUTB

1111 1111 1111

+V

IN

⎛

⎝⎜

2047

2048

⎞

⎠⎟

1000 0000 0001

1000 0000 0000

0111 1111 1111

+V

IN

⎛

⎝⎜

1

2048

⎞

⎠⎟

0V

−V

IN

⎛

⎝⎜

1

2048

⎞

⎠⎟

0000 0000 0000

−V

IN

⎛

⎝⎜

2048

2048

⎞

⎠⎟

=

−V

IN

–5–

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