AD8383

Rev. 0 | Page 8 of 16

THEORY OF OPERATION

TRANSFER FUNCTION AND ANALOG OUTPUT VOLTAGE

The DecDriver has two regions of operation: where the video

output voltages are either above or below a reference voltage

VMID, and where VMID = (V1 + V2)/2. The transfer function

defines the analog output voltage as the function of the digital

input code as follows:

⎟

⎠

⎞

⎜

⎝

⎛

×

=

1023

–

1

)

(

n

FS

V

–

V1

n

VIDx

for INV = LOW

⎟

⎠

⎞

⎜

⎝

⎛

×

+

=

1023

–

1

)

(

n

VFS

2

V

n

VIDx

for INV = HIGH

where n = input code

VFS = 2 × (VREFHI – VREFLO)

A number of internal limits define the usable range of the

analog output voltages, VIDx, as shown in Figure 5.

To best correlate transfer function errors to image artifacts, the

overall accuracy of the DecDriver is defined by two parameters,

VDE and VCME.

VDE, the differential error voltage, measures the difference

between the rms value of the output and the rms value of the

ideal. The defining expression is

[

][

]

VFS

n

1

V

n

VOUTP

2

V

n

VOUTN

n

VDE

×

⎟

⎠

⎞

⎜

⎝

⎛ −

−

−

−

−

=

1023

1

2

)

(

)

(

)

(

VCME, the common-mode error voltage, measures ½ the dc

bias of the output. The defining expression is

()

⎥⎦

⎤

⎢⎣

⎡

+

+

=

2

–

)

(

)

(

2

1

2

1

)

(

2

V

1

V

n

VOUTP

n

VOUTN

n

VCME

INPUT CODE

AGND

V1

V2

AVCC

0

1023

0

≤ V

0

≤ V

5V

≤ V2 ≤ (AVCC – 4)

5V

≤ V1 ≤

(AVCC – 4)

9V

≤ AVCC ≤ 18V

≥ 1.3V

≥ 1.3V

INV = HIGH

INV = LOW

INTERNAL LIMITS AND

USABLE VOLTAGE RANGES

Figure 5. Transfer Function, VIDx vs. Input Code, Internal Limits and Usable Output Voltage Range