# Tuning of transconductance in OTA circuit

1. ## Tuning of transconductance in OTA circuit

Hi

I want to tune the transconductance of OTA. For transconductance tuning I have to vary the biasing current but How can I vary the biasing current what circuitry should be used to vary the biasing current for transconductance tuning.

2. ## Re: Tuning of transconductance in OTA circuit

Do you speak about a commercial OTA unit?
In this case, the data sheet gives you some information about the corresponding pin and the internal voltage at this pin.

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3. ## Re: Tuning of transconductance in OTA circuit

Originally Posted by LvW
Do you speak about a commercial OTA unit?
In this case, the data sheet gives you some information about the corresponding pin and the internal voltage at this pin.
No, I am taking about the schematic diagram to simulate in CADENCE. How can I tune the biasing current? There might be some tuning circuitry that can be varied which can tune the transconductance.

4. ## Re: Tuning of transconductance in OTA circuit

How about a variable current source?

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5. ## Re: Tuning of transconductance in OTA circuit

Originally Posted by FvM
How about a variable current source?
Yes, but after simulating I have to fabricate chip I think while to fabricate the circuit we might have to use some tunable circuitry to vary the biasing currents? The current source can not be fabricated like this? This is what I understood Correct me if I am wrong?

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6. ## Re: Tuning of transconductance in OTA circuit

How about a simple (large) resistor?
Do you need linear tuning?

7. ## Re: Tuning of transconductance in OTA circuit

Yes I need linear tuning.

How simple resistor vary the bias current. If resistor value fixed then tuning is not possible. Normally OTA are electronically tunable. There biasing currents can be tuned. I also want to tune the biasing current.

OTA is electronically tunable. I want to tune the OTA biasing current how can I tune that. The tuning circuitry in different research articles are not shown. What circuit can be designed/used to tune the biasing of OTA.

8. ## Re: Tuning of transconductance in OTA circuit

Hi,

Did you read and try post#4?

Klaus

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9. ## Re: Tuning of transconductance in OTA circuit

Originally Posted by KlausST
Hi,

Did you read and try post#4?

Klaus
How can I design a variable current source. I have provided biasing of the OTA simply by using current mirrors so I have a fixed current. For tuning how can I design a variable current source. I have to fabricate the OTA.

10. ## Re: Tuning of transconductance in OTA circuit

Normally OTA are electronically tunable. There biasing currents can be tuned. I also want to tune the biasing current.
Typical OTA ICs have current mirror inputs for bias setting

You didn't yet mention what's the characteristic of the involved tuning source. If it's a voltage source and you want a linear tuning characteristic, you'll design a linear V/I converter. I presume it's discussed somewhere in your analog design text books.

11. ## Re: Tuning of transconductance in OTA circuit

Hi mate, You can use current mirror based binary DAC topology.

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