Electronic – What’s the catch with these JFETs

analogjfetlow-noise-amplifierRF

I'm designing a low-noise, high-bandwidth (100 MHz) pre-amp using JFETs. The choice for JFETs was because it needs to operate with large source impedances (>10 kΩ).

I spent a while looking for a suitable JFET (high g, low input C, good noise-figure). I came across ones from CEL (for example, the CE3520K3 (datasheet, home page) with g = 50 mS , NF = 0.5). They don't specify input capacitance, but it must be sub-pF given the operational frequencies. What's the catch? The datasheet does specify large gate currents, so current shot noise will be high. Does anyone have experience working with such devices?

Best Answer

There are no catches (lol) Only Specs

The s-parameters start at 2GHz 

CEL
! CE3520K3
! N-channel HJ-FET
! Vds = 2 V Id = 6 mA
# Hz S  MA   R 50
!      f            S11               S21               S12               S22
!    Hz        MAG       ANG       MAG       ANG        MAG        ANG       MAG       ANG
2000000000 0.98035944 -29.159311 4.3293347 149.29152 0.02862794 67.64743 0.65920687 -24.487707

What is the purpose?

In the meantime, WHAT's ALL THIS STUFF ABOUT ...?

GaAs pHEMT JFETs

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It's just balancing act

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A delicate balancing act.

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Just start with good Design Specs, including DFM, DFT , then perform DVT and if passes all tests. Congrats, Its Perfect. enter image description here

or startover until it passes your design specs.

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Or do it right the 1st time with better specs.

REF

20 Years ago HP R&D came up with this

To address the growing handset power amplifier needs for the emerging Personal Communications Services (PCS) markets, a 3-volt, single-supply, enhancement-mode pseudomorphic high-electron-mobility transistor (E-PHEMT) has been developed.

The device exhibits +33dBm output power and 65% drain efficiency at 1.88 GHz.

Consider a state of the art FET buffered Differential Probe specs enter image description here

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Using MGF4919G enter image description here enter image description here REF

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