Effect on the output using a TL 072 op-amp

[gazp1988]

Homework Statement

Replace the ideal op-amp by the TL 072 [the default op-amp] and note the effect upon the output. Can you explain it?

Homework Equations

The Attempt at a Solution

i can see there is a large spike on the output volts of the trans-impedance op-amp using the TL 072 op-amp. however I am struggling to explain why.
here is the what the waveform looked like using an ideal op-amp

 

[berkeman]

Homework Statement

Replace the ideal op-amp by the TL 072 [the default op-amp] and note the effect upon the output. Can you explain it?

Homework Equations

View attachment 97897

The Attempt at a Solution

i can see there is a large spike on the output volts of the trans-impedance op-amp using the TL 072 op-amp. however I am struggling to explain why.
here is the what the waveform looked like using an ideal op-amp
View attachment 97899

What analysis are you running there? You just want to get the DC setpoints, right? And the results for the ideal opamp look wrong -- how can -1nA through the 10M resistor and the 10:1 divider give you something * 10^-30? The result for the TL070 opamp looks more reasonable...

 

[gazp1988]

the output for the ideal op-amp is 100mv
the output for the TL072 is *10^-30.
im running simetrix.

 

[berkeman]

the output for the ideal op-amp is 100mv
the output for the TL072 is *10^-30.
im running simetrix.

Ah, sorry, I got them backwards. There must be some hookup problem with the TL072 schematic. Why are there blue X's on the input & output connections for the ideal opamp schematic, but not on the TL072 version?

 

[berkeman]

Also, can you probe all of the DC voltages in the circuit for each circuit?

 

[gazp1988]

the blue is because the op-amp was highlighted at the time it makes no difference to the output.
each circuit has a dc voltage probe on it next to the marker.

 

[berkeman]

each circuit has a dc voltage probe on it next to the marker.

I only see the output node probe. What about all of the other nodes?

 

[berkeman]

Also, are the power supplies hooked up correctly? In Micro-Cap SPICE, I have to make explicit connections to device terminals. See how your +/- power terminal inputs still have open squares on them? Doesn't that mean they have nothing connected to them yet?

 

[gazp1988]

this is how i connect up the power supply and I've put makers on each probe

 

[berkeman]

View attachment 97933
this is how i connect up the power supply and I've put makers on each probe

Can you probe the power supply terminals of the opamp? I still think they are not connected...

 

[gazp1988]

 

[berkeman]

Why are they only +/-10mV?

 

[gazp1988]

because that is the input we were given for the circuit

 

[berkeman]

because that is the input we were given for the circuit

No way. The power supply rails for an opamp need to be in the +/-12V range. Not 10mV. Set them to +/-12V for both simulations and see what happens.

 

[gazp1988]

i see what what i ahev done now the original question stated "Calculate the current I to give an output voltage of 0.1 V if Rf = 10 MΩ, R1 = 90 kΩ, R2 = 10 kΩ." I've taken 0.1v as the input voltage.

 

[berkeman]

i see what what i ahev done now the original question stated "Calculate the current I to give an output voltage of 0.1 V if Rf = 10 MΩ, R1 = 90 kΩ, R2 = 10 kΩ." I've taken 0.1v as the input voltage.

So what are you going to set as your power supply values now? Do both simulations work now with +/-12V rails?

 

[gazp1988]

changing the voltage to +/-12 has no difference to the output?

 

[berkeman]

It looks like you have the + & - voltage rails swapped?

 

[gazp1988]

ive restructured it now

 

[berkeman]

Looks to be working better! Now you can look into the small errors that the TL072 has versus the ideal opamp. What numbers do you get for the ideal opamp circuit now?

 

[gazp1988]

 

[gazp1988]

it seems that there is some initial output interference could it be caused because of output noise??