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I'm considering evaluating the NXP BGA28xx series MMIC for my application, a fixed-frequency special purpose AM receiver, because

  • they're cheap
  • they're very simple to wire up
  • they claim to be internally matched to 50 ohms without even specifying what frequency that would apply to
  • they claim operation down to 0Hz, and I'm between 1-10MHz which is too low for some MMICs

Is this too good to be true? How is it possible for this device to be automatically matched over its entire range? Would it be suitable for a basic, low bandwidth LNA?

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  • \$\begingroup\$ can you give a link to the product page at NXP, or the datasheet? \$\endgroup\$ – The Photon May 10 '18 at 23:17
  • \$\begingroup\$ Yep, interesting family of amplifiers, thanks. But they don't say how well they match 50 Ohms.... \$\endgroup\$ – Ale..chenski May 11 '18 at 1:43
  • \$\begingroup\$ @AliChen, the one datasheet I looked at (BGA2866) has (typical) Smith charts for S11 and S22. \$\endgroup\$ – The Photon May 11 '18 at 1:47
  • \$\begingroup\$ @ThePhoton, funny, 2869 nor 2817 don't have any charts... \$\endgroup\$ – Ale..chenski May 11 '18 at 2:08
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they claim to be internally matched to 50 ohms without even specifying what frequency that would apply to

I looked at two datasheets for these parts.

Both have input and output return loss specs at 250, 950, and 2150 MHz.

One of them had typical Smith charts for S11 and S22 for the same span of frequencies.

How is it possible for this device to be automatically matched over its entire range?

A resistive termination with low capacitive parasitics will be matched across a wide band.

Would it be suitable for a basic, low bandwidth LNA?

That seems to be the application they sell them for.

If you're not using the full band, you likely want to filter the output to avoid capturing noise in the portion of the amplifiers gain band that you aren't using.

I'm between 1-10MHz which is too low for some MMICs

Given they don't give any specs below 250 MHz, you might want to get the eval board and test them out before you commit to designing them in.

Unfortunately they don't say much about the internal circuit from which you could make guesses about how to use it at low frequencies.

They seem to use external inductance in the VCC line to tweak the performance. You might want to try adding some additional inductance there to get good results at very low operating frequencies. Or conversely you might need higher bypass capacitance to give a clean VCC voltage at such a low frequency. Experimentation (or perhaps a call to your local NXP applications engineer) is in order.

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  • \$\begingroup\$ They mention applications below 100 MHz, in section to select the caps. \$\endgroup\$ – Ale..chenski May 11 '18 at 2:10
  • \$\begingroup\$ @AliChen, they say it's possible, but do they give any specs? I saw where they recommend higher value dc blocking caps. \$\endgroup\$ – The Photon May 11 '18 at 2:15
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In general MMIC amplifiers are only limited in the low frequency range by your blocking capacitors. To size them, just make sure the capacitive reactance (1/(2 * pi * f * c) at your frequency is much less than 50 ohms. In recent years there have been some built for very high frequencies that don't go down to DC, but if the data sheet doesn't mention this then you're probably OK. The inductor in the VCC line is there to keep you from dissipating your signal power in the biasing resistor. Here what you want to do is make sure the inductive reactance at your frequency (2 * pi * f * l) is much bigger than 50 ohms.

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