[time-nuts] TAPR TICC boxed (input protection)

David davidwhess at gmail.com
Sun Apr 9 14:17:36 EDT 2017

On Sat, 8 Apr 2017 16:30:38 -0400, you wrote:

>David wrote:
>> I mentioned this in connection with some manufacturers using gold
>> doping in transistors which would not normally be expected to have
>> gold doping.  So you end up with a bunch of lessor named 2N3904s which
>> meet the 2N3904 specifications but are useless if you were looking for
>> low leakage diodes.
>I believe all 2N3904s and 2N3906s are gold doped.  National's certainly 
>were (Processes 23 and 66), and TI's and Fairchild's are. Not heavily 
>doped, like 2N2369s (with storage times of ~20nS), but just enough to 
>bring the storage time down to ~100nS.   2N2219s, 2N2222s, and 2N4401s 
>are also lightly gold doped.

I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola.  I wish detailed process
information like National had was available from every manufacturer.

What was funny was when we did this, the lower frequency transistors
that I tested like the 2N5088/9 were much worse.

>> If [4117 leakage is] not being tested, then where is the maximum specified
>> leakage number coming from?  For a small signal bipolar transistor it
>> will typically be 25nA, 50nA, or 100nA, but the InterFET datasheet (1)
>> shows 10pA maximum and 1pA maximum for the A versions.
>>        *   *   *
>> When this discussion of low leakage input protection started, I did a
>> quick search for inexpensive alternatives to the 4117/4118/4119 JFETs
>> and came up with nothing; all of the inexpensive JFETs are much worse
>Same as any "guaranteed by design" spec -- by the device design. The 
>4117 series is unlike any other JFET -- the geometry is TINY, and the 
>4117 Idss is only 30-90uA (hundreds of times lower than other low-Idss 
>JFETs). [BTW, lowest Idss is why I recommend the 4117 over the 4118 and 
>4119 for use as a low-leakage diode.  The 4118 and 4119 have higher Idss 
>-- up to 240uA for the 4118 and 600uA for the 4119 -- and tend to have 
>higher gate leakage, as well.]
>Best regards,

If the 10pA specification is guaranteed by design, then wouldn't they
have to be testing the 1pA "A" parts?

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