Hello guys , I'm designing a 3-bit digital to analog converter using an R2R ladder .The problem is when I'm using the op-amp as a buffer, the input signal and output signal are not same . I'm using 5 V for both the ladder and the op-amp. What may be the problem ?

 

Hello,

Can you post the complete schematic, including the supply voltages?
Is the supply a single 5 Volts?
The specs of the opamp say a minimum voltage of ± 3 Volts dual supply or 6 Volts single supply.
The opamp has an offset of about 4 mV max.
There is no scale on your graph.

Bertus

 

Hello,

Can you post the complete schematic, including the supply voltages?
Is the supply a single 5 Volts?
The specs of the opamp say a minimum voltage of ± 3 Volts dual supply or 6 Volts single supply.
The opamp has an offset of about 4 mV max.
There is no scale on your graph.

Bertus

Here is the schematic and graph:this is from serial plotter in arduino IDE . 0-1023 is 0-5 V

 

Hello,

Can you post the complete schematic, including the supply voltages?
Is the supply a single 5 Volts?
The specs of the opamp say a minimum voltage of ± 3 Volts dual supply or 6 Volts single supply.
The opamp has an offset of about 4 mV max.
There is no scale on your graph.

Bertus

I programmed the Arduino to input the following 000,001,010,011,.......,111,000,.... the red dots on my graph is the voltage for each binary number. The peak is not 111 , the next dot below is 111 and i don't know why the op-amp outputs a lower voltage .I tried other op-amps of same type and also used a 9 V battery for the op-amp .Again the input and output voltage are not same.

 

Hello,

If you want to work on +5 volts only, you will need to choose an other opamp with rail-to-rail capabilities.



Bertus

 

Hello,

You are introducing failures in the graph, by using 4k7 resistors in stead of real 5K resistors (wich can be made with 2 10K resistors in parallel).

Bertus

 

Hello,

You are introducing failures in the graph, by using 4k7 resistors in stead of real 5K resistors (wich can be made with 2 10K resistors in parallel).

Bertus

For the resistors I tried with 1M and 2M with same results. I will try to use the LM358 op-amp. I also used 9V battery for the NE5532 . see the picture below.

 

I tested the op-amp again and it is buffering correctly above 1.5 V , if Vin < +1.5 V it goes fully crazy and V out becomes +Vcc. Thanks for all your quick replies and I hope using a rail to rail will be able to buffer 0-5 V correctly. I'm taking longer to test other op-amps because of the availability of components in my country