RC Integrator with Opamp or OTA

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parkpika

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The traditional RC integrator is implemented with an ideal opamp with RC. I've seen some integrators with OTA with the same RC configuration.

Why does this work? OTA has high output impedance right?
 

parkpika said:
I've seen some integrators with OTA with the same RC configuration.

Why does this work? OTA has high output impedance right?
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Where did you see such a circuit? It definitely does not work as an integrator.
The classical OTA integrator uses a capacitive load at the high resistive output.
(Of course, no ideal integration because of the finite output impedance).
 

Where did you see such a circuit? It definitely does not work as an integrator.
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It depends. With sufficient gm, the circuit can fairly work as an integrator. But why should we omit the output stage that turns an OTA into a voltage amplifier?

It neither makes much sense to ask this as a general question, I think. You better calculate the transfer function of circuit with specific parameters and decide if it's good as for the intended usage.
 
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FvM said:
With sufficient gm, the circuit can fairly work as an integrator. .
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Yes - I was in error. For gm>>wC the circuit can be used as an integrating device - however for the lower frequency band only (w<<gm/C).

EDIT: The above applies for idealized conditions only (ideal current source).
For real devices (output resistance odf 100kohms or lower) the situation changes "nearly dramatically". That means: a practical usage is allowed in a rather small frequency band only - depending on the selected parts values and the chosen transconductance gm.
 
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