Diode-Connected Transistors [Design]

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From: John Larkin on 21 Jul 2010 01:28

On Wed, 21 Jul 2010 15:18:13 +1000, Grant <omg(a)grrr.id.au> wrote:

>On Tue, 20 Jul 2010 18:02:54 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote:
>
>>Got an E-mail from Grant advising that I promised a comparison of the
>>various ways of doing Diode-Connected Transistors. So here it is...
>>
>>www.analog-innovations.com/SED/DiodeConnectedTransistors.pdf
>>
>> ...Jim Thompson
>
>John L. was going to check BJT diode performance back on the thread:
>
>>Subject: Re: Types of diode-connected BJTs
>>Date: Fri, 09 Jul 2010 08:04:56 -0700
>>Message-ID: <1hee36hr0l0mm2dri4eml98is3mntfidld(a)4ax.com>
>>...
>>I'll try the BFT25 with the emitter open and shorted to the base, when
>>I get a chance. I'd be interested in comparing both leakage and
>>capacitance. As I mentioned, fA leakage testing is tedious.
>
>Hope you find time for this one John?
>
>I though Jim T. was going to do something with these too, now he has.
>
>Might've been a different thread that I can't find?
>
>
>Time flies differently when one is having all their teeth ripped
>out :)
>
>Grant.

No, but because of popular demand, I'll try to do it tomorrow. Spice
sims aren't especially surprising at high currents. And not likely to
be very accurate at sub-pA currents.

I did measure capacitance, BFT25 both ways. The numbers were something
like 0.5 and 1 pF.

John

From: Robert Baer on 21 Jul 2010 04:29

From: Jim Thompson on 21 Jul 2010 10:58

On Tue, 20 Jul 2010 22:28:59 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>On Wed, 21 Jul 2010 15:18:13 +1000, Grant <omg(a)grrr.id.au> wrote:
>
>>On Tue, 20 Jul 2010 18:02:54 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote:
>>
>>>Got an E-mail from Grant advising that I promised a comparison of the
>>>various ways of doing Diode-Connected Transistors. So here it is...
>>>
>>>www.analog-innovations.com/SED/DiodeConnectedTransistors.pdf
>>>
>>> ...Jim Thompson
>>
>>John L. was going to check BJT diode performance back on the thread:
>>
>>>Subject: Re: Types of diode-connected BJTs
>>>Date: Fri, 09 Jul 2010 08:04:56 -0700
>>>Message-ID: <1hee36hr0l0mm2dri4eml98is3mntfidld(a)4ax.com>
>>>...
>>>I'll try the BFT25 with the emitter open and shorted to the base, when
>>>I get a chance. I'd be interested in comparing both leakage and
>>>capacitance. As I mentioned, fA leakage testing is tedious.
>>
>>Hope you find time for this one John?
>>
>>I though Jim T. was going to do something with these too, now he has.
>>
>>Might've been a different thread that I can't find?
>>
>>
>>Time flies differently when one is having all their teeth ripped
>>out :)
>>
>>Grant.
>
>No, but because of popular demand, I'll try to do it tomorrow. Spice
>sims aren't especially surprising at high currents. And not likely to
>be very accurate at sub-pA currents.

Only because most discrete-device manufacturers don't characterize
their products at those currents... if they characterize at all.
Mostly they just leave out those terms.

Win Hill complains regularly about poor MOSFET models. Those
manufacturers respond by supplying add-on elements in a subcircuit.
They _should_have characterized them as HSpice_48/PSpice_7/BSIM3v3. I
have demonstrated here, in the past, a size-scaled I/C MOSFET so that
it behaves much like a 2N7000, _and_ has appropriate gate-charge
behavior.

>
>I did measure capacitance, BFT25 both ways. The numbers were something
>like 0.5 and 1 pF.
>
>John

John, Please tell us how you are measuring capacitance in Spice.

I have a quite precise way that separates real and imaginary parts. I
use this primarily to characterize amplifier inputs when tuned
circuits are involved. Spice aficionados contact me via E-mail and
I'll share.

Spice is like a sports car... only as good as the person behind the
wheel.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

From: Joel Koltner on 21 Jul 2010 13:23

Thanks Jim... I'm surprised just *how much* better the BE_C_FLOAT case is than
the others.

....although BC_EB_SHORT is best for low currents... interesting...

From: Jim Thompson on 21 Jul 2010 14:05

On Wed, 21 Jul 2010 10:23:40 -0700, "Joel Koltner"
<zapwireDASHgroups(a)yahoo.com> wrote:

>Thanks Jim... I'm surprised just *how much* better the BE_C_FLOAT case is than
>the others.
>
>...although BC_EB_SHORT is best for low currents... interesting...

Caution: I didn't characterize transient behavior. Floating elements
tend to cause "funny" storage times.

And "best" is in the eye of the beholder :)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

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