inverting opamp compensation

[pona]

I am trying to simulate a circuit in ORCAD including basic inverting operational amplifier whose gain is 250 and input is 10mV. The opamp used is LM124. The output should be -2.5V but when I simulate it the output is -167.68mV. I have also used a compensation circuit consisting of a resistor whose value is parallel combination of R1 and Rf. But the result is not much different. What can be the possible reason?

 

[LvW]

What kind of supply? Single or double?

 

[pona]

Single supply of 20V

 

[himansg]

Single supply of 20V

If you are using single supply of 20 V i.e. +20V - gnd , then you cannot get output lower then 0V.
Use supply of +10 to -10 V

 

[Milad-D]

Instead of (+20,0), you can use (+10,-10).

 

[pona]

yes now it gives correct output. Whats the reason behind using dual supply?

 

[Milad-D]

Just imagine that the output of op-amp should provide negative voltages(let us say -5volts) for positive input voltages but the supply voltages are (20,0). The output voltage must be in the supply rail range.

 

[LvW]

The reason is simply: Design. (Think, for example, of a simple npn amplifying stage that needs a positive supply voltage.)
The opamp is designed for split supply operation. That means: Without any additional bias circuitry the dc output voltage (quiescent point) is at 0 volts and, thus, it can swing to positive and negative values.

 

[pona]

okay thanks a lot