[SOLVED] Getting more current in a bias block design

[DharmaSlice]

Hi,

So I have a bias block I designed to provide 80uA of current into a 20K resistor. I have ported the same block to a 1V1 process but the branch now only gives me 20uA. And no matter how I change the dimensions I can never get above 45uA. I must have an incorrect approach. I am looking for help on how to approach the redesign of this block please.

Any help would be great.

 

[crutschow]

You should label the components so they can be easily referenced.

The two bottom transistors look like a current-mirror that need a connection to common. Is that true?

 

[DharmaSlice]

Hi,

So I labeled the devices better.

 

[erikl]

... provide 80uA of current into a 20K resistor. ... 1V1 process ... I can never get above 45uA. I must have an incorrect approach.

45µA into 20kΩ eats up 0.9V of your supply, so just 0.2V left for both transistors. How much is the Vth of your process?

 

[DharmaSlice]

45µA into 20kΩ eats up 0.9V of your supply, so just 0.2V left for both transistors. How much is the Vth of your process?

Threshold voltage at the gate is 200mV at least. I need an overdrive voltage of 200mV. I guess I will need to look again at my load resistance level in order to keep the transistors in saturation.

 

[pfd001]

The current is limited by the supply voltage. If you want to increase the current, you should decrease the resistor.