Does anyone has the spice model for the AD648 OP-AMP (or similar)

Thank you

Fausto Bartra

Does anyone has the spice model for the AD648 OP-AMP (or similar)

Thank you

Fausto Bartra

Hello Fausto,

You can use ADA4062-2 as a recommended alternative parts. It's a low power JFET dual op amp with a readily available SPICE model.

Please let us know if you have any more question.

Thanks,

Phil

Fausto,

If you have instability at 200 Hz, it's your big loop, and not anything particular w/ the op amp.

You can try a simulation with the ADA4062-2 as suggested, and then try a faster op amp,

the ADA4610-2. Finally, try a much slower bipolar with low IB, the AD8622.

For the integrator stage, the simulator may have problems finding a DC bias point, so you may

have to use a .IC spice directive on the integrator output set to zero volts. You can also, in the sim,

and in real life, add a large resistor (1meg?) across the 1uF cap to form a "leaky integrator" or a low

pass filter. I don't know if this would be acceptable in your system or not. Finally, If you are running

on +/-15V and the integrator is integrating up and down, and the output gets to +10V or -10V, then the

cap is charged up. If you turn off the system and the power supplies drop to zero rapidly, the cap

will discharge backwards into the output and destroy the part. Maybe one time out of a thousand,

but I did have a customer with this type of failure several years ago. The good news is the 1.69k

resistor will limit the current so you might not have a problem.

A problem that has been there since day one is the heavy load on the output, you have less than

1k. (R4/R4A) The AD648 has a wimpy output stage; the spec table has output swing w/ a 10k load.

Your output is much lower; see the graph.

Q) What's on the other side of D7???

We totally rewrote the photodiode tool last year and it's very good; so if you have the specs

for your photodiode, try it out:

PHOTODIODE CIRCUIT DESIGN WIZARD | Analog Devices

Another good site for TIAs is: JavaScience Consulting Services

He has some good calculators there.

Harry

Fausto,

If you have instability at 200 Hz, it's your big loop, and not anything particular w/ the op amp.

You can try a simulation with the ADA4062-2 as suggested, and then try a faster op amp,

the ADA4610-2. Finally, try a much slower bipolar with low IB, the AD8622.

For the integrator stage, the simulator may have problems finding a DC bias point, so you may

have to use a .IC spice directive on the integrator output set to zero volts. You can also, in the sim,

and in real life, add a large resistor (1meg?) across the 1uF cap to form a "leaky integrator" or a low

pass filter. I don't know if this would be acceptable in your system or not. Finally, If you are running

on +/-15V and the integrator is integrating up and down, and the output gets to +10V or -10V, then the

cap is charged up. If you turn off the system and the power supplies drop to zero rapidly, the cap

will discharge backwards into the output and destroy the part. Maybe one time out of a thousand,

but I did have a customer with this type of failure several years ago. The good news is the 1.69k

resistor will limit the current so you might not have a problem.

A problem that has been there since day one is the heavy load on the output, you have less than

1k. (R4/R4A) The AD648 has a wimpy output stage; the spec table has output swing w/ a 10k load.

Your output is much lower; see the graph.

Q) What's on the other side of D7???

We totally rewrote the photodiode tool last year and it's very good; so if you have the specs

for your photodiode, try it out:

PHOTODIODE CIRCUIT DESIGN WIZARD | Analog Devices

Another good site for TIAs is: JavaScience Consulting Services

He has some good calculators there.

Harry