Re: FW: [SI-LIST] : FIXED: curve tracers and Output Impedance

Sandy Taylor (ataylor@rolyat)
Mon, 6 Apr 1998 10:49:25 -0700 (PDT)

The X axis is voltage, the Y axis is current, just like
a real curve tracer. the current goes non linear
when the input protection diodes turn on.

Here is what a good driver output looks like:

> Iout |
> | |
> | /
> | /
> | /
> | /
> | /
> | /
> |/
> --------------- Vout
> /
> |
> |
> The flattening out is due to the diode clamping.

The schematic Vadim suggested is too simple.
We have active circuits connected to Vout that create
a very nice linearized output which is also controlled
to match to 50 ohms over process voltage (VDD) and temperature.

That is what it takes to push the limits of performance.
These drivers are also used as activer terminators,
so the AC characteristics are important over voltage.
Just characterizing the DC current at a single point is
not enough.

I will ask for permission from Sun to send .ps files of the spice
output to the alias. Ascii would not do it justice.

Sandy Taylor

> From: "Heyfitch, Vadim" <vadim.heyfitch@intel.com>
> To: "'si-list@silab.Eng.Sun.com'" <si-list@silab.Eng.Sun.COM>
> Subject: FW: [SI-LIST] : FIXED: curve tracers and Output Impedance
> Date: Mon, 6 Apr 1998 09:32:22 -0700
> Importance: high
> X-Priority: 1
> MIME-Version: 1.0
>
>
> > I think the initial curve Sandy Taylor drew was correct. That is if we
> > agree on the meaning of those variables on the axes.
> >
> If Vout is the DS voltage, and Iout is the drain current. While the gate
> voltage is tied high, raising the drain-source voltage will cause Id go up
> linearly at first and then saturate. The TAN^(-1) of the slope in the linear
> region is Ron of the driver.
> > A strong driver has a steep curve (low Ron).
> > high
> > | d------------- Vout
> > | |
> > | _|
> > g|--|_
> > |
> > |
> > s
> >
> > Vadim Heyfitch