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Electronics => Projects, Designs, and Technical Stuff => Topic started by: the_eagle on December 01, 2018, 02:58:01 pm

Title: Estimate power consumption
Post by: the_eagle on December 01, 2018, 02:58:01 pm

I have a symmetrical OTA as shown in the image attached. At a high level we can consider it similar to an op-amp so golden rules apply.

The current source (I_ref) generates a supply of 100uA from 5V and V_b is 1.55V. If the output is 2.5V (the midrail voltage) in open loop configuration with input 2.5V and 2.497V for V+ and V- respectively. How can I estimate the power consumption of the device?

Using the golden rules, we know that there is no input current in the op-amp input terminals; but then I get stuck on how to combine power dissipated by the current source and V_b.

Title: Re: Estimate power consumption
Post by: Wimberleytech on December 01, 2018, 06:44:46 pm

Here you go.  Vb does not cost anything if you design it as I have shown.

Title: Re: Estimate power consumption
Post by: the_eagle on December 02, 2018, 11:34:18 am

So those extra 550uA (650uA - Iref) are taken from the power supply of Iref, is it correct?

Title: Re: Estimate power consumption
Post by: Wimberleytech on December 02, 2018, 12:22:09 pm

If Iref is not sourced from Vdd, then the total Vdd current is 550 ua

Title: Re: Estimate power consumption
Post by: the_eagle on December 03, 2018, 01:54:42 am

I understood the reasoning process! Thank you very much!