measure the parameters of op amp using LT SPICE

[deepsetan]

hai guys..this is the circuit that i've created for my mini project..basically, i want to create the macromodel for this circuit..by using LT SPICE software..how can I actually measured the output and input impedance for this circuit?..i also need to measure the input current and the voltage gain as well..as there are many pins in this op amp, which pin should i consider to measure the parameters needed? Vp, Vm, VBIAS 1 or VBIAS 2:--(..

 

[Audioguru]

You need an opamp that works from a supply as low as 2.5V and you need models of its parameters. It would help if you had the datasheet for the opamp.

 

[D.A.(Tony)Stewart]

I would think using a sweep generator with AC coupled high R to simulate a current source and measured voltage could be used to compute V/I impedance on any port.

 

[Audioguru]

I have used thousands of opamps but not one that works with a supply as low as only 2.5V.
Some opamps have Fet inputs so their input impedance is infinite.
A few opamps work with an input at the negative supply voltage which is ground in the circuit shown.
Usually an opamp is used with plenty of negative feedback so the output impedance is extremely low.
The voltage gain of an opamp with no negative feedback is 200,000 to millions at DC and at low frequencies so it would be VERY difficult to bias and to measure.

 

[crutschow]

I have used thousands of opamps but not one that works with a supply as low as only 2.5V.
........................

For your interest here is one that states it works down to 1.8V.

Another interesting low-voltage device I have is a SR5-59 Sony AM/FM radio which works well on a single 1.5V AA battery. It has excellent sound (headphones only) and works down to about 1V battery voltage before it dies (after about a 100 hours of operation). How they can get a complex analog RF/audio IC such as that to work down to 1V is a mystery.

 

[deepsetan]

I have used thousands of opamps but not one that works with a supply as low as only 2.5V.
Some opamps have Fet inputs so their input impedance is infinite.
A few opamps work with an input at the negative supply voltage which is ground in the circuit shown.
Usually an opamp is used with plenty of negative feedback so the output impedance is extremely low.
The voltage gain of an opamp with no negative feedback is 200,000 to millions at DC and at low frequencies so it would be VERY difficult to bias and to measure.

i try to measure the input impedance by using ac analysis..does this graph to seem be correct?..20 db will give me 10 ohm as the impedance..

 

[FvM]

Vout/Vdd transfer function doesn't look like an impedance quantity...

 

[deepsetan]

I would think using a sweep generator with AC coupled high R to simulate a current source and measured voltage could be used to compute V/I impedance on any port.

how about this??..:-D:-D:-D

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basically, i'm just current source with the fixed magnitude of 1 A to measure the output impedance..:???:

 

[FvM]

Yes, that's output impedance. You hopefully know if the curve makes sense for this amplifier. Is it an OTA?

I also hope that setting the bias point without DC feedback is suitable for it.

 

[deepsetan]

Yes, that's output impedance. You hopefully know if the curve makes sense for this amplifier. Is it an OTA?

I also hope that setting the bias point without DC feedback is suitable for it.

how about the input impedance??..can i just connect a resistor from my input?..:grin::grin: