A digital to analog converter that uses an R-2R ladder circuit is known as a ladder DAC. This circuit uses only two types of resistors, one having resistance R and the other having 2R.
Hence, the precision of the resistors is not as stringent as what is needed for the weighted-resistor DAC. Schematic representation of an R-2R ladder DAC.
In this case the switching circuit can operate just like in the previous case of weighted-resistor DAC.
To obtain the input-output equation for the ladder DAC, suppose that, as before, the voltage output from the solid-state switch associated with bi of the
Then, the purpose of the DAC isto generate an output voltage (signal level) that has this numerical value, and maintain the value until the nextdigital word is converted into the analog form. Since a voltage output cannot be arbitrarily large or small forpractical reasons, some form of scaling would have to be employed in the DAC process.
This scale will dependon the reference voltage uref used in the particular DAC circuit.
A typical DAC unit is an active circuit in the integrated circuit form and may consist of a data register (digital circuits), solid-state switching circuits, resistors, and operational amplifiers powered by an external power supply, which can provide the reference voltage for the DAC.
The reference voltage will determine the maximum value of the output (fullscale voltage). As noted before, the integrated circuit (IC) chip that represents the DAC is usually one of many components mounted on a printed circuit (PC) board, which is the input/output (I/O) board (or, I/O card; or, interface board; or, data acquisition and control board).
This board is plugged into a slot of the data acquisition and control PC.
There are many types and forms of DAC circuits. The form will depend mainly on the manufacturer, and requirements of the user or of the particular application.