OTA as an integrator

[salil87]

Hi
I just want to get some idea how to use an OTA as an integrator (for dual slope ADC). Can some one help me out or give me some links?
Thanks
Salil

 

[yuvan]

OTA is indeed a integrator when connected to a cap; gmvd current pumped into cap...

 

[FvM]

LInearity of OTAs without feedback is generally low, mostly due to the nonlinear transconductance curve. I can't imagine that it will give more than 1% (7-Bit) accuracy for a dual slope ADC. In other words, a bad idea.

 

[LvW]

As in case of a classical operational amplifier you also can use a capacitor in the negative feedback path of an OTA. In addition, you need buffering the output. When the input voltage is applied to the inverting OTA input through a resistor R the voltage transfer function is:H(s)=1/(1+gm*R) - 1/s[(C/gm +RC)]. Gm is the transconductance of the OTA. The second term is equivalent to an inverting integrator. For low frequencies the first term can be neglected in case the product gm*R is small enough.