11

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12-Bit Serial Daisy-Chain D/A Converter

8143

07.23.03 REV 3

Equivalent Circuit Analysis

Figures 12 and 13 show equivalent circuits for the 8143 internal DAC with all bits LOW and HIGH, respectively. The

reference current is switched to IOUT2 when all data bits are LOW, and to IOUT1 when all bits are HIGH. The ILEAK-

AGE current source is the combination of surface and junction leakages to the substrate. The 1/4096 current source

represents the constant 1-bit current drain, through the ladder’s terminating resistor.

Output capacitance is dependent upon the digital input code. This is because the capacitance of a MOS transistor

changes with applied gate voltage. This output capacitance varies between the low and high values.