> On Wed, 23 Aug 2017 04:35:58 -0700 (PDT), pcdhobbs@gmail.com wrote:
>
>>> Do you happen to have any data on the RF performance or gate leakage?
>>
>> I always run JFETs at about 2.5V D-S, to get full transconductance with minimal heating and no avalanche gate leakage. In that mode the CPH3910 has higher transconductance and lower capacitance than the BF862, and about the same leakage, i.e. a couple of picoamps at room temperature.
>>
>> BF862s run well at I_DSS, so I've sometimes used an op amp to adjust the tail current to zero out V_DS. That way you can take the output straight from the bootstrap if you like, and of course it's good for IR photodiodes that don't like reverse bias.
>>
>> With an I_DSS of about 30 mA vs around 12, CPH3910s run a bit warm at 0 V D-S, so it's less attractive to do that.
>>
>> Cheers
>>
>> Phil Hobbs
>
> V_DS?? You mean V_GS??
Yes, of course, thanks. I said V_DS was 2.5V.
Cheers
Phil Hobbs
--
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ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
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hobbs at electrooptical dot net
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Reply by Jim Thompson●August 23, 20172017-08-23
On Wed, 23 Aug 2017 04:35:58 -0700 (PDT), pcdhobbs@gmail.com wrote:
>>Do you happen to have any data on the RF performance or gate leakage?
>
>I always run JFETs at about 2.5V D-S, to get full transconductance with minimal heating and no avalanche gate leakage. In that mode the CPH3910 has higher transconductance and lower capacitance than the BF862, and about the same leakage, i.e. a couple of picoamps at room temperature.
>
>BF862s run well at I_DSS, so I've sometimes used an op amp to adjust the tail current to zero out V_DS. That way you can take the output straight from the bootstrap if you like, and of course it's good for IR photodiodes that don't like reverse bias.
>
>With an I_DSS of about 30 mA vs around 12, CPH3910s run a bit warm at 0 V D-S, so it's less attractive to do that.
>
>Cheers
>
>Phil Hobbs
V_DS?? You mean V_GS??
...Jim Thompson
--
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Reply by ●August 23, 20172017-08-23
>Do you happen to have any data on the RF performance or gate leakage?
I always run JFETs at about 2.5V D-S, to get full transconductance with minimal heating and no avalanche gate leakage. In that mode the CPH3910 has higher transconductance and lower capacitance than the BF862, and about the same leakage, i.e. a couple of picoamps at room temperature.
BF862s run well at I_DSS, so I've sometimes used an op amp to adjust the tail current to zero out V_DS. That way you can take the output straight from the bootstrap if you like, and of course it's good for IR photodiodes that don't like reverse bias.
With an I_DSS of about 30 mA vs around 12, CPH3910s run a bit warm at 0 V D-S, so it's less attractive to do that.
Cheers
Phil Hobbs
Reply by David Nadlinger●August 23, 20172017-08-23
On 23.08.17 12:49 AM, pcdhobbs@gmail.com wrote:
> Thanks for the heads-up. Fortunately ON recently introduced the CPH3910, which is about 1 dB better than the BF862 for my uses.
Do you happen to have any data on the RF performance or gate leakage?
I've seen it mentioned by audio people, but the datasheet seems a bit
sparse. I'll definitely test a few as well in my circuit, but I'd have
to build a test jig to directly measure the parameters (although that's
probably a useful thing to have anyway).
— David
Reply by David Nadlinger●August 22, 20172017-08-22
On 23.08.17 1:17 AM, pcdhobbs@gmail.com wrote:
>> NXP is probably "not recommended for new designs."
>
> Since Nexperia didn't take the BF862, I was sort of expecting this.
I was wondering about this as well (especially as they market it as
being for AM car radios). But then, all the RF-ish stuff remained at
NXP, so… —David
Reply by ●August 22, 20172017-08-22
>NXP is probably "not recommended for new designs."
Since Nexperia didn't take the BF862, I was sort of expecting this.
Cheers
Phil Hobbs
Reply by Joerg●August 22, 20172017-08-22
On 2017-08-22 16:49, pcdhobbs@gmail.com wrote:
> Thanks for the heads-up. Fortunately ON recently introduced the
> CPH3910, which is about 1 dB better than the BF862 for my uses.
>
Thanks, duly noted. Some day I'll have to try that in a very low voltage
oscillator application. The BF862 excels in that domain as well (motes,
energy harvesting and so on).
> Anyway, I just ordered 3 reels of the one and 4 of t'other for
> insurance.
>
Thanks for the heads-up. Fortunately ON recently introduced the CPH3910, which is about 1 dB better than the BF862 for my uses.
Anyway, I just ordered 3 reels of the one and 4 of t'other for insurance.
Cheers
Phil Hobbs
Reply by ●August 22, 20172017-08-22
On Tuesday, August 22, 2017 at 11:24:01 AM UTC-4, David Nadlinger wrote:
> Looks like NXP are phasing out the BF862:
> http://www.nxp.com/pages/n-channel-fet:BF86X?tab=Package_Quality_Tab
>
> Any alternatives in mind for simple low-noise transimpedance frontends
> and bootstraps? Having just started to design things using the BF862, I
> quite liked the fact that you can get reasonable noise performance
> without having to deal with (bootstrap/…) huge amounts of drain capacitance.
>
> I'm looking for something with <1 nV/rtHz wideband noise and a 1/f knee
> significantly below 1 MHz, <10 pF input capacitance, sensible gate
> leakage and a few 100 MHz of bandwidth. Maybe the CPH3910 (ON Semi)?
> They don't seem to quote any RF performance figures, though.
>
> — David
On Tue, 22 Aug 2017 16:23:57 +0100, David Nadlinger
<david@klickverbot.at> wrote:
>Looks like NXP are phasing out the BF862:
>http://www.nxp.com/pages/n-channel-fet:BF86X?tab=Package_Quality_Tab
>
>Any alternatives in mind for simple low-noise transimpedance frontends
>and bootstraps? Having just started to design things using the BF862, I
>quite liked the fact that you can get reasonable noise performance
>without having to deal with (bootstrap/�) huge amounts of drain capacitance.
>
>I'm looking for something with <1 nV/rtHz wideband noise and a 1/f knee
>significantly below 1 MHz, <10 pF input capacitance, sensible gate
>leakage and a few 100 MHz of bandwidth. Maybe the CPH3910 (ON Semi)?
>They don't seem to quote any RF performance figures, though.
>
> � David
NXP is probably "not recommended for new designs."
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