Datasheet

TLV5621I
LOW-POWER QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTER
SLAS138B – APRIL 1996 – REVISED FEBRUARY 1997
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
linearity, offset, and gain error using single-end supplies
When an amplifier is operated from a single supply, the voltage offset can still be either positive or negative. With
a positive offset, the output voltage changes on the first code change. With a negative offset the output voltage
may not change with the first code depending on the magnitude of the offset voltage.
The output amplifier attempts to drive the output to a negative voltage. However, because the most negative
supply rail is ground, the output cannot drive below ground and clamps the output at 0 V.
The output voltage then remains at zero until the input code value produces a sufficient positive output voltage
to overcome the negative offset voltage, resulting in the transfer function shown in Figure 5.
DAC Code
Output
Voltage
0 V
Negative
Offset
Figure 5. Effect of Negative Offset (Single Supply)
This offset error, not the linearity error, produces this breakpoint. The transfer function would have followed the
dotted line if the output buffer could drive below the ground rail.
For a DAC, linearity is measured between zero-input code (all inputs 0) and full-scale code (all inputs 1) after
offset and full scale are adjusted out or accounted for in some way. However, single supply operation does not
allow for adjustment when the offset is negative due to the breakpoint in the transfer function. So the linearity
is measured between full-scale code and the lowest code that produces a positive output voltage. The code is
calculated from the maximum specification for the negative offset.
equivalent inputs and outputs
GND
V
ref
Input
V
DD
To DAC
Resistor
String
_
+
V
DD
DAC
Voltage Output
I
SINK
60 µA
Typical
84 kΩ
84 kΩ
× 1
× 2
Output
Range
Select
Input from
Decoded DAC
Register String
INPUT CIRCUIT OUTPUT CIRCUIT
GND