Let b3 be the most significant bit and thus is connected to the +5V and all the other switchs are connected to the ground. Digital to Analog Converter with R and 2R ResistorsĪ D/A converter with R and 2R resistors is shown in the figure below.Īs in the binary-weighted resistors method, the binary inputs are applied by the switches (b0-b3), and the output is proportional to the binary inputs.īinary inputs can be either in the HIGH (+5V) or LOW (0V) state. This is why R and 2R method is more preferred as it requires only two sets of precision resistance values. If the number of inputs (>4) or combinations (>16) is more, the binary-weighted resistors may not be readily available.
The only condition to look out for is that the maximum output voltage should not exceed the saturation levels of the op-amp. Thus, a desired size for a step can be obtained by connecting the appropriate feedback resistor. The value of the feedback resistor R f changes the size of the steps. In practice, due to the variations in the logic HIGH voltage levels, all the steps will not have the same size. The output is a negative going staircase waveform with 15 steps of -0.5V each. The graph with the analog outputs versus possible combinations of inputs is shown below. The output will be maximum if the switches (b0-b3) are closed. This overall current is then converted to its proportional output voltage. The current through R f will be the sum of these currents. Thus, according to the position (ON/OFF) of the switches (bo-b3), the corresponding “binary-weighted” currents will be obtained in the input resistor.