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Design >> Analog Design >> Which is the better way to bias many identical circuit blocks?
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Message started by yong_rfic on Nov 5^th, 2012, 2:11pm

Title: Which is the better way to bias many identical circuit blocks?
Post by yong_rfic on Nov 5^th, 2012, 2:11pm

Hi guys,
I have many identical building blocks, like differential pairs, which are relatively far away from each other (e.g., 100um on the layout) . How to bias all these tail transistors to ensure that a good matching of dc operation point is achieved?
I can think of two ways. First is to use a current mirror for each of the differential pair, and tie all the current mirrors' Vdd together. Another approach is to use a single current mirror and feed the gate voltage to all the tail transistors' gate.
There seems to be another way which feeds the current to instead of voltage to locally generate the bias voltage, but I dont know whether this approach is necessary here.
Thanks!

Title: Re: Which is the better way to bias many identical circuit blocks?
Post by urian on Nov 6^th, 2012, 8:45am

It depends on the distance for which method to use. From Grey, he said that currents are routed globally and voltages locally. In other words, bias currents are routed between blocks and bias voltages within the blocks.

urian

Title: Re: Which is the better way to bias many identical circuit blocks?
Post by loose-electron on Nov 7^th, 2012, 1:11pm

distribute bias via current methods for two reasons -

Proximity matching and ground noise.