very low operational transconductance amplifier (OTA)

[iamadog]

operational transconductance amplifier

Hi,

I am trying to design a very low operational transconductance amplifier (OTA) (~10nA/V) for Gm-C filter in a low frequency. Does anyone know how to design such OTA as from my calculations I obtained a W/L ratio of 0.00098 which is incredibly small?

I read about a paper saying that an inversion level of 10 for the drivers (M1, M2 which is the input transistor) in order to obtain the required transconductance (~10nA/V)? Does anyone know what does the author means by that sentence?

Thanks and I really appreciate for the helps.

 

[iamxo]

very low frequency ota design

I think it's to say the input transistor should work in weak inversion region.

 

[iamadog]

ota weak inversion region

Any idea of how long of Veff one can go when designing such amplifier?

Sorry. I am still new to analog filters and this is actually my first time designing an integrated filter. Does anyone know what are the advantages and disadvantages in using a switched cap technique and using a transconductance filter in terms of area and power?

Thanks. really appreciate it.

 

[DenisMark]

designing of ota

10nA/V looks like impossible low. Check your specification. Inversion coefficient == 10 means strong inversion, when overdrive voltage Vov~0.2V (u use Veff term). Keep in mind that when Vov~0.5V and goes higher it's possible velocity saturation effect. In this region transconductance becomes independent of current exept W/L ratio.

Try to look for and read papers firstly:

 

[solidstate]

transconductance amplifier

Maybe you can use gm subtraction: two diff pairs with one gm = 100 nS and the other 90 nS connected in opposite polarity. 100nS is easier to implement than 10 nS, for sure... however, this will typically require some work to guarantee gm over PVT..

And on the inversion thing: the stronger inverted the device, the lower its gm/Id --> the more inefficiently the current is used; that's what you want in this case.

If your system lets you, you could also consider duty cycle operation of a larger gm (1 uS 1% of the time, for example)

 

[iamadog]

operational transconductance amplifier ota

Hi guys, I just found out about the replies. It is getting late now and I might try to understand about the posted replies above.

Anyway, my biggest challenge now is also to think of a way to design a high pass integrated filter with an extremely low cut off frequency ~ 0.05 Hz. I know it is quite impossible as I had read a lot of papers and I believe no one had ever done that before. Most of the authors suggested using an external cap to implement it due to the large capacitor in IC. But any ideas,suggestions or techniques are welcomed.

Thanks so much guys

 

[ordinaryman]

ota+operational transconductance amplifiers

hey man, i was browsing the search results on this forum and came across to your post. I'm also trying to design low frequency filter (below 100Hz). Do you have suggestion on which technique may be used? I'm new in here, so please advice