On 2/14/2013 8:04 AM, Spehro Pefhany wrote:
> On Wed, 13 Feb 2013 19:56:34 -0800, the renowned josephkk
> <joseph_barrett@sbcglobal.net> wrote:
>
>> On Wed, 13 Feb 2013 11:16:46 -0800, John Larkin
>> <jlarkin@highlandtechnology.com> wrote:
>>
>>> On Wed, 13 Feb 2013 13:41:34 -0500, Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>> On 2/13/2013 12:27 PM, John Larkin wrote:
>>>>> On Wed, 13 Feb 2013 11:34:36 -0500, Phil Hobbs
>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>
>>>>>> On 2/13/2013 11:30 AM, John Larkin wrote:
>>>>>>> On Wed, 13 Feb 2013 11:01:28 -0500, Phil Hobbs
>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>
>>>>>>>> On 2/13/2013 10:24 AM, John Larkin wrote:
>>>>>>>>> On Tue, 12 Feb 2013 21:57:13 -0800, josephkk <joseph_barrett@sbcglobal.net>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> On Tue, 12 Feb 2013 11:59:36 -0500, Phil Hobbs
>>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>>>>
>>>>>>>>>>> On 02/11/2013 05:29 PM, mike wrote:
>>>>>>>>>>>> On 2/11/2013 10:42 AM, Phil Hobbs wrote:
>>>>>>>>>>>>> Hi, all--I'm looking for a curve tracer. Ideally it would be
>>>>>>>>>>>>> USB-powered, and come with software that would make plots and generate
>>>>>>>>>>>>> data files. Nothing too fancy, just I_C and I_B vs V_CE and V_BE, and
>>>>>>>>>>>>> the equivalent for FETs. A plus would be automatic computation of beta,
>>>>>>>>>>>>> V_GSth, Early voltage, and even some of the DC SPICE parameters like
>>>>>>>>>>>>> emitter and base resistance.
>>>>>>>>>>>>>
>>>>>>>>>>>>> It would be especially nice if it could measure gate current with a
>>>>>>>>>>>>> resolution of a picoamp or less.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Any suggestions?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Cheers
>>>>>>>>>>>>>
>>>>>>>>>>>>> Phil Hobbs
>>>>>>>>>>>>>
>>>>>>>>>>>> You're asking a LOT.
>>>>>>>>>>>>
>>>>>>>>>>>> A curve tracer is a qualitative measurement device.
>>>>>>>>>>>> I use a TEK 7CT1N for simple stuff and only drag out the 576
>>>>>>>>>>>> when I gotta have it. I use it more for blowing shorts
>>>>>>>>>>>> out of NiCd's than for testing transistors.
>>>>>>>>>>>
>>>>>>>>>>> It's only qualitative because it only has a CRT readout. A curve tracer
>>>>>>>>>>> is a sort of stripped-down version of a semiconductor parameter analyzer
>>>>>>>>>>> such as an HP4145B, which is very quantitative indeed. (I wouldn't mind
>>>>>>>>>>> one of those--I used to have one at my PPOE, but it takes a lot of rack
>>>>>>>>>>> space.)
>>>>>>>>>>>>
>>>>>>>>>>>> If you try to make one using a series of fixed measurements
>>>>>>>>>>>> and graphing them, you get mixed results. I tried that back in the day.
>>>>>>>>>>>> The device thermal time constants significantly affect the measurement
>>>>>>>>>>>> details.
>>>>>>>>>>>
>>>>>>>>>>> Yup. You have to be quick about it if you're dissipating any
>>>>>>>>>>> significant power. Of course with a MCU and DACs, you can do the
>>>>>>>>>>> measurements out of order to keep the average dissipation constant.
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> And the parasitics of the test fixture swamp device parasitics, unless you
>>>>>>>>>>>> use network analyzer fixturing.
>>>>>>>>>>>
>>>>>>>>>>> Not necessarily. My Boonton 72BD easily measures a few femtofarads.
>>>>>>>>>>> You just null it out before attaching the hot lead to the device.
>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Picoamps to amps is a wide dynamic range and will require some serious
>>>>>>>>>>>> attention to range switching.
>>>>>>>>>>>>
>>>>>>>>>>>> Not saying it can't be done, just that it's not nearly as simple as it
>>>>>>>>>>>> sounds.
>>>>>>>>>>>
>>>>>>>>>>> I don't need amps--I'd be quite happy with a 50-100 mA top end. Most of
>>>>>>>>>>> what I need a curve tracer for is measuring weird RF devices with lousy
>>>>>>>>>>> datasheets.
>>>>>>>>>>>
>>>>>>>>>>> Cheers
>>>>>>>>>>>
>>>>>>>>>>> Phil Hobbs
>>>>>>>>>>
>>>>>>>>>> Oh foo, the fixturing for RF devices can get really weird and expensive.
>>>>>>>>>> Those will be on you if we get together and create a USB curve tracer.
>>>>>>>>>>
>>>>>>>>>> ?-)
>>>>>>>>>
>>>>>>>>> The problem with a lot of (most) RF devices is their terrible DC
>>>>>>>>> characterization. Like, no DC curves at all. The s-params give you a rough idea
>>>>>>>>> of the high-speed behavior.
>>>>>>>>>
>>>>>>>>> RF data sheets often say to just adjust the bias until it works. The specified
>>>>>>>>> breakdown voltage specs are not useful, because sometimes they assume, without
>>>>>>>>> saying so, that the drain voltage can swing to multiples of the supply voltage,
>>>>>>>>> and factor that in. Parts spec'd at 6 volts can cheerfully avalanche at 25. A
>>>>>>>>> detector diode might be spec'd a 2 volts reverse, woth no curves at all, because
>>>>>>>>> they figure that's all a detector user needs to know.
>>>>>>>>
>>>>>>>> I'm normally working down on the low frequency end anyway, e.g. a 100
>>>>>>>> MHz biochip front end using 14-GHz pHEMTs and 40-GHz bipolars, so simple
>>>>>>>> concepts like C_JC and R_BB' still work OK. Boontons rule!
>>>>>>>
>>>>>>> Right. You have to make your own curves, like C-vs-V. That's why a USB
>>>>>>> curve tracer should measure capacitances, too.
>>>>>>>
>>>>>>> Heck, somebody here with a curve tracer and a Booonton could set up a
>>>>>>> garage operation to characterize parts for a fee. Modelithics does
>>>>>>> that for big bucks.
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> Have you measured the leakage of the Boonton's biasing system? Maybe
>>>>>> one could just hang a little board on the back of one, and do it that way.
>>>>>>
>>>>>> Cheers
>>>>>>
>>>>>> Phil Hobbs
>>>>>
>>>>> Good idea. Design the USB curve tracer to run through a Boonton 72 to
>>>>> get the capacitances. The Boonton has an analog output on the back.
>>>>> But it would be more fun to do it ourselves.
>>>>>
>>>>>
>>>>
>>>> Sure, I'm in. Do you think it might actually sell?
>>>>
>>>
>>> Well, some for sure. Ten a year? 200?
>>>
>>> Time to start scribbling.
>>
>> We might make two or more models. Some dependency on price, features, and
>> performance for sales outside this ng. Within the ng we could probably
>> make and deploy one to two dozen. Then with real world experience i
>> think we could do a better job of selling it outside.
>>
>> ?-)
>
> How practical do you think it would it be to add temperature
> characterization? I'd be interested in that.
Just a SMOP. Measure Delta V_BE at three known currents, dancing back
and forth as needed to take out the effects of drift and R_E. Should be
able to get Theta_JA and maybe the thermal mass of the die + paddle.
I'd like to be able to measure noise as well.
It will be interesting to figure out how to make a test fixture that
prevents all transistors from oscillating under all conditions. Maybe
the thing to do is to sell the tracer cheap and make money off the
disposable test boards. (Shades of early IBM.)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058
hobbs at electrooptical dot net
http://electrooptical.net