Digital Analog Converter (DAC)

Instead of using a pre-made DAC, a 4 bit digital to analogue convertor will be used which will have the same set up as that of an inverting summing amplifier. Building a DAC is cheaper and we can easily cater for any adjustments to the resistance values if needed compared to an already built DAC.
A summing amplifier which consists of an operational amplifier (op-amp) and 5 resistors will be used, 4 resistors in parallel and 1 is a feedback resistor. A 3.3V input voltage rail will be connected to switches to the first 4 resistors and the summing amp system will be used were the output voltage will be between 3.3V and 5V. An inverting op-amp will be used to invert the voltage provided from the normal op-amp from a negative feedback to a positive feedback.
The DAC is set up to allow the DAC to turn on if the Vout is above 0.6V. R5 will have a resistance value of 12Ω. One of the resistors set in the parallel side of the circuit will have a resistance of 90kΩ whilst the other three resistors are going to be at values of 1.155kΩ, 2.31kΩ and 4.62kΩ.
Due to the high resistor values that are going to be used, there is a great chance that the resistors, if too small, will produce a backing current which we do not want for the circuit, or if too big it will dissipate unwanted heat. Hence this is the reason why values are in the range of kΩ.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-Share Alike 2.5 License.