RF PNP transistor

[sdouble]

Hi everybody,
I'm currently designing a cascode amplifier. Actually, I intend to build a folded cascode amplifier. It will be based on a j-FET and a RF transistor. To allow for more headroom, I do want to use a low noise RF PNP transistor.
It seems that there is not a single RF PNP on the market anymore. How is that possible ?!?

[Benta]

My crystal ball just broke 

Voltage?
Power level?
Frequency?
...

[MasterT]

https://www.digikey.ca/products/en/discrete-semiconductor-products/transistors-bipolar-bjt-rf/283?k=&pkeyword=&sv=0&pv74=2&sf=0&FV=ffe0011b&quantity=&ColumnSort=0&page=1&pageSize=25

[sdouble]

My crystal ball just broke 

What happened to your crystal ball ?
I personnally prefer coffee grounds readings. more reliable and less prone to falling from a height.

Voltage?
Power level?
Frequency?

very low power/low voltage/current (3 V, 15 mA)
600 MHz min

[Benta]

600 MHz min

F_T or operating frequency? Your question does not get better...

[sdouble]

3db cutoff frequency

[Zero999]

The BFT92, only because I've got some in my junk box.

[Gerhard_dk4xp]

Intersil / Renesas HFA31... transistor arrays have the last fast PNPs.  ft = 5 GHz or so.

I still have a reel of BFG31   

Regards, Gerhard

[T3sl4co1l]

MMBTH81, get 'em before they're gone forever.  Only fT is up there, mind.

BFT92 may still be around in places.  (I have some in my bin too, actually; good luck..)

Your alternatives are, do it with NPNs anyway (consider SiGe HBTs, or PHEMTs, or GaAs or GaN FETs, with fT in the 10s of GHz -- may not need cascode), or do it monolithic (custom IC, or find a commercial all-in-one solution that you can adapt to your application).

Tim

[sdouble]

I have some spare BFT92 around too. But I do need to design a new equipment. I need to source "active" components only.
I had to give up with the modern HBT, PHEMTs, GaAs FET due to their leakage current. This prevent from using them at relatively low frequencies (below say 100 MHz).
My current plane is to cascode a good ol' "high-gm" JFET with a very low noise SiGe HBT from Infineon. Those could be prone to oscillate in the GHz range. We'll see.

 

MMBTH81, get 'em before they're gone forever.  Only fT is up there, mind.

BFT92 may still be around in places.  (I have some in my bin too, actually; good luck..)

Your alternatives are, do it with NPNs anyway (consider SiGe HBTs, or PHEMTs, or GaAs or GaN FETs, with fT in the 10s of GHz -- may not need cascode), or do it monolithic (custom IC, or find a commercial all-in-one solution that you can adapt to your application).

Tim

[T3sl4co1l]

Phil Hobbs is fond of cascoding two of them, afraid I forget which though.  One of them has awful Early effect (or the FET equivalent), so that goes on the bottom; the other doesn't, but has awful low frequency noise, so goes on the top.  Yes, the layout must be tight and usually demands a small ferrite bead on the base/gate, which must be carefully chosen since you still want some high frequencies, not just lower ones.

Tim