3-lead Transistor for high frequency?

[circuit_hunter]

Hi

I want to test some ideas, where I would like to feed an RF signal into the source terminal of transistor (the way we do it in common gate configuration). And, my frequency is not very specific, but say in the range of 1GHz-2GHz. I thought of using ATF-34143, but it is 4-lead pHEMT where two terminals serve as source. So I can't use it.

I searched online , but I couldn't find any 3 lead transistor to play around with. I have two questions:

(1) Why do they make two source terminals? For better heat sink?

(2) Could you please suggest me any alternative transistor, if they exist at all, with only 3 leads (one for each source, gate and drain) whose ADS model is also available for download ?


Thanks.

 

[betwixt]

The second source pin is usually to keep the impedance to the surrounding circuit as low as possible. Effectively, the second pin is in parallel with the other one so it's inductance is halved. Only in the cae of high power transistors is it used as an additional heat conductor but devices like the ATF-34143 are for relatively low power applications.

Why can't you use a four pin device and link the source pins together? It will improve performance even in a common gate configuration.

Brian.

 

[BigBoss]

Infineon has pretty large RF transistor portfolio.
https://www.infineon.com/cms/en/pro...html?channel=ff80808112ab681d0112ab6b2b24074e

 

[circuit_hunter]

The second source pin is usually to keep the impedance to the surrounding circuit as low as possible. Effectively, the second pin is in parallel with the other one so it's inductance is halved. Only in the cae of high power transistors is it used as an additional heat conductor but devices like the ATF-34143 are for relatively low power applications.

Am I right, if In infer from your reply that the two source pins are internally connected? Just like many ground vias in PCB, they are effectively in parallel?

Why can't you use a four pin device and link the source pins together? It will improve performance even in a common gate configuration.

I thought of doing that, but if I later decide to really use this transistor, I was wondering about its possible layout in ADS momentum. If sources are used as ground, I can easily put some vias. But if have to fed signal into them, how will I connect the two source pins together as they are diagonally opposite. Pardon me if I sound a bit naïve, but I have not fabricated any active components so far. One option, perhaps would be to connect using a bit isolated ground plane trace, but it will create defect in the ground and I am not sure about resulting performance.

To save myself from dealing with this issue, I am looking for a transistor with only 3 leads.

Infineon has pretty large RF transistor portfolio.
https://www.infineon.com/cms/en/pro...html?channel=ff80808112ab681d0112ab6b2b24074e

I did check 3-4 transistors in online store that were from Infineon, but they were all, again, 4 leads. Now, you have sent me a direct link, I will search it there. Thanks.

 

[betwixt]

Yes, they are internally linked, in fact in many if not all devices, the pin runs right through the package and the die is bonded to it.

In most instances the source pins are grounded so the layout has an 'in' side and 'out' side with a ground running between them. Vias are added if the ground isn't topside of the board. In the four pin devices you should still be able to use just one of the source pins, maybe with slightly reduced performance or there should be space under the package to bridge them with a track. The problem may be the lack of signal isolation as the in and out will be in such close proximity.

Brian.