digital to analog converters 



A D/A converter using binaryweighted resistors is shown in the figure below. In the circuit, the opamp is connected in the inverting mode. The opamp can also be connected in the noninverting mode. The circuit diagram represents a 4digit converter. Thus, the number of binary inputs is four. We know that, a 4bit converter will have 24 = 16 com
binations of output. Thus, a corresponding 16 outputs of analog will also be present for the binary inputs. Thus, according to the position (ON/OFF) of the switches (bob3), the corresponding binaryweighted currents will be obtained in the input resistor. The current through Rf will be the sum of these currents. This overall current is then converted to its proportional output voltage. Naturally, the output will be maximum if the switches (b0b3) are closed The output is a negative going staircase waveform with 15 steps of ). 5V each. In practice, due to the variations in the logic HIGH voltage levels, all the steps will not have the same size. The value of the feedback resistor Rf changes the size of the steps. Thus, a desired size for a step can be obtained by connecting the appropriate feedback resistor. The only condition to look out for is that the maximum output voltage should not exceed the saturation levels of the opamp. Metalfilm resistors are more preferred for obtaining accurate outputs. If the number of inputs (>4) or combinations (>16) is more, the binaryweighted resistors may not be readily available. This is why; R and 2R method is more preferred as it requires only two sets of precision resistance values. A D/A converter with R and 2R resistors is shown in the figure below. As in the binaryweighted resistors method, the binary inputs are simulated by the switches (b0b3), and the output is...
characters left: