questions about op-amp!!!!!

[bryant83]

hi all:
i am now connecting a DAC circuit and for the o/p at the R-2R network is producing a current o/p and i need a voltage o/p. so, i will be using an op-amp with a Rf to do the job. so i would like to ask whether i could use the 741C instead of TL0-81 to do the job? help needed thanks in advance!!

 

[bryant83]

DAC means digital to analog converter. TL0-81 is an op-amp then the Rf is the feedback resistor connected between the inverting i/p and the o/p of the op-amp. (bcos the o/p of the DAC will be current and i want to convert the current to a voltage. i read some reference books and they add an op-amp to the o/p of the DAC but they used TL0-81, so i would like to ask whether could i use a 741C instead of TL0-81?)

sorry that i did not make clear message!!!!!!

 

[ljcox]

Yes a 741 will do the job. BUT, it is a bipolar Op-Amp, so the Thevenin resistance of the resistors connected to the positive input must be equal to that of the negative input in order to cancel the effect of the input bias currents.

If these Thevenin resistances are not equal, there will be an offset and it will vary with temperature.

The TL081 is a FET input so the bias currents are very small and so this issue is not critical.

Len