Chuffed told us that in post #26. The instructor is apparently unaware that the inverting configuration only has BW of 500 kHz. He simply bridged the inverting and non-inverting amps to the load with no frequency shaping.

I don't think we know that "He (the instructor) simply bridged the inverting and non-inverting amps to the load with no frequency shaping." What Chuffed said about his instructor's solution, namely "...this was basically the set up.", seems me too vague to infer that much detail. That's why I asked Chuffed to tell us "...what exactly did the instructor give as the answer?"

 

Your reading comprehension is very different from mine.

 

Sorry, been pretty busy so forgot to check back. Have another class about to start, so when I get a chance I'll snap a picture of his answer for the question.

 

Picture might be a little big, we'll see. But this is his answer to the problem.

 

... this is his answer to the problem.

Does not satisfy the 1Mhz Bandwidth requirement if the two amplifiers have only a 1MHz Gain Bandwidth Product.

Every Engineer worthy of the name occasionally has to break the news to the boss that they are wrong. Seems like I had to this repeatedly...

 

View attachment 91886
Picture might be a little big, we'll see. But this is his answer to the problem.

Would you ask your instructor what is inside the triangle labeled "Av=-1"? If it's the usual topology for a inverting op amp stage without any capacitors, does he realize the BW is not 1 MHz?

 

Now my answer feels a lot less like cheating.
Regards

 

He seems pretty dead set on his answer. Just kind of brushed the question aside, saying that it's completely possible.

 

He seems pretty dead set on his answer. Just kind of brushed the question aside, saying that it's completely possible.

Then he's not only ignorant, he's arrogant.

 

Well, he's also the type of guy who sees students forgetting to label pins on schematics for the first lab as "failing miserably."
If that tells you anything.

 

He seems pretty dead set on his answer. Just kind of brushed the question aside, saying that it's completely possible.

Invite your professor to this thread and we can ask for his proof.

My original thought of it being possible has been cast aside as the model I used is being suspect.

 

This single opamp circuit has a low frequency gain of 2, a bandwidth of about .85 MHz, and a GBWP greater than 1 MHz while using an opamp with a GBWP of 1 MHz. How is this possible?

It almost meets the problem's requirements with a single opamp and a load that isn't floating.

 

I would point out that the instructor's solution, shown in post #44, only shows generalized gain blocks of gain +1 and -1. He has labeled those blocks as having bandwidths of 1 MHz. He doesn't show the details of just how his inverting gain block achieves a bandwidth of 1 MHz. We know that it is possible to do so thanks to Russmax. The instructor could claim that his inverting gain block uses some method, such as Russmax's, that does in fact have a bandwidth of 1 MHz. If he has the standard inverting topology with resistors only, no capacitors, we know that the bandwidth is less than 1 MHz, but who knows what the instructor might say at this point.

 

Well, he's also the type of guy who sees students forgetting to label pins on schematics for the first lab as "failing miserably."
If that tells you anything.

Then I would probably add "anal retentive" to the mix.

 

You could modify the 10 MHz GBW op amp discussed here to 1 MHz GBW and still not achieve what the professor stated.

That furthers my suspicion of the uA741 model in my simulator that I used in my first posting in this thread.

Maybe the professor can join us and demonstrate that it can be done.

Attached is the simulation from the above modified model

 

You could modify the 10 MHz GBW op amp discussed here to 1 MHz GBW and still not achieve what the professor stated.

That furthers my suspicion of the uA741 model in my simulator that I used in my first posting in this thread.

Maybe the professor can join us and demonstrate that it can be done.

Attached is the simulation from the above modified model

Try adding a 15.9 pF capacitor across your R2.

 

Already did. Still interested in the professor's topology.

 

Already did.

Are you going to post the result?

 

here is the module used ....

* 10 MHz GBW from eCircuitCenter
* Modified to 1 MHz GBW (Changed CP1)
*
* connections: non-inverting input
* | inverting input
* | | output
* | | |
.SUBCKT 1MHZ-GBW 1 2 6
* INPUT IMPEDANCE
RIN 1 2 10MEG
* DC GAIN=100K AND POLE1=100HZ
* UNITY GAIN = DCGAIN X POLE1 = 1MHZ
EGAIN 3 0 1 2 100K
RP1 3 4 1K
CP1 4 0 15.915UF
* OUTPUT BUFFER AND RESISTANCE
EBUFFER 5 0 4 0 1
ROUT 5 6 10
.ENDS

... and the results.

 

This single opamp circuit has a low frequency gain of 2, a bandwidth of about .85 MHz, and a GBWP greater than 1 MHz while using an opamp with a GBWP of 1 MHz. How is this possible?

It almost meets the problem's requirements with a single opamp and a load that isn't floating.

Here's one that does seem to meet the problem's requirements (except that the rolloff isn't exactly a single pole .....):