AD394

Rev. A | Page 7 of 12

THEORY OF OPERATION

The AD394 quad DAC provides four-quadrant multiplication.

It is a hybrid IC comprised of four, monolithic, 12-bit, CMOS,

multiplying DACs and eight precision output amplifiers. Each

of the four independent-buffered channels has an independent

reference input capable of accepting a separate dc or ac signal

for multiplying or for function generation applications. The

CMOS DACs act as digitally programmable attenuators when

used with a varying input signal or, if used with a fixed dc

reference, the DAC would act as a standard bipolar output DAC.

In addition, each DAC has a 12-bit wide data latch to buffer the

converter when connected to a microprocessor data bus.

MULTIPLYING MODE

Figure 5 shows the transfer function. The diagram indicates an

area over which many different combinations of the reference

input and digital input can result in a particular analog output

voltage. The highlighted transfer line in the diagram indicates

the transfer function if a fixed reference is at the input. The

digital code above the diagram indicates the midpoint and

endpoints of each function. The relationship between the

output is given in Table 4. Note that the reference input signal

sets the slope of the transfer function (and determines the full-

scale output at code 111...111), while the digital input selects the

horizontal position in each diagram.

Figure 5. The AD394 as a Four-Quadrant Multiplier

of Reference and Digital Input

DATA AND CONTROL SIGNAL FORMAT

The AD394 accepts 12-bit parallel data in response to Control

Signals CS1–CS4. As detailed in Table 3, the four chip select

lines are used to address the DAC register of interest. It is per-

missible to have more than one chip select active at any time. If

CS1–CS4 are all brought low coincident, all four DAC outputs

will be updated to the value located on the data bus. All control

inputs are level-triggered and may be hard-wired low to render

any register (or group of registers) transparent.

Table 3. DAC Select Matrix

CS1

CS2

CS3

CS4

Operation

1

1

1

1

All DACs latched

0

1

1

1

Load DAC 1 from data bus

1

0

1

1

Load DAC 2 from data bus

1

1

0

1

Load DAC 3 from data bus

1

1

1

0

Load DAC 4 from data bus

0

0

0

0

All DACs simultaneously loaded

Table 4. Bipolar Code Table

Data Input

Analog Output

1111

1111

1111

⎭

⎬

⎫

⎩

⎨

⎧

2048

2047

9.9951 V

Full Scale − 1 LSB

1100

0000

0000

⎭

⎬

⎫

⎩

⎨

⎧

2048

1024

5.000 V

1/2 Scale

1000

0000

0001

⎭

⎬

⎫

⎩

⎨

⎧

2048

1

4.88 mV

1 LSB

1000

0000

0000

⎭

⎬

⎫

⎩

⎨

⎧

2048

0

0.000 V

Zero

0111

1111

1111

⎭

⎬

⎫

⎩

⎨

⎧

2048

1

−4.88 mV

−1LSB

0100

0000

0000

⎭

⎬

⎫

⎩

⎨

⎧

2048

1024

−5.000 V

−1/2 Scale

0000

0000

0000

⎭

⎬

⎫

⎩

⎨

⎧

2048

2048

−10.000 V

−Full Scale