Other NXP ProductsのトピックRe: MRF101 - How to modify the reference circuits?

MRF101 - How to modify the reference circuits?

SaaifK — Tue, 27 Apr 2021 18:27:37 GMT

Hello everyone,

I am a junior engineer who is completely new to the world of RF. I am trying to use the MRF101 to replace an obsolete transistor in a circuit used for plasma generation. The current system works in the FM band, but instead of having a range of 87.5Mhz to 108Mhz, it uses the Japanese system which begins at 76Mhz.

I am trying to modify a reference circuit of the MRF101 in order to have it operate in the range from 76Mhz to 108Mhz. If anyone can give me a starting point or some tips on how to do this, I would really appreciate it. The MRF101 seems to have quite a large operating range, so I believe this should be possible.

If anyone has any ideas, please let me know!

Re: MRF101 - How to modify the reference circuits?

LPP — Thu, 06 May 2021 11:45:45 GMT

Sure, the NXP circuit can be tuned to extend frequency low bound. Current circuit has maximum input return loss at 87MHz. It can be shifted to 76MHz by modifying L1=36nH to L1=47nH.

Best Regards,

Pavel

NXP CAS

Re: MRF101 - How to modify the reference circuits?

SaaifK — Thu, 06 May 2021 19:06:35 GMT

Thank you so much Pavel! I really appreciate it! I will definitely give this a try and report back how well it works. Does lowering the inductance further reduce the low frequency cutoff? Any insight you can give me on this will be immensely helpful!

Re: MRF101 - How to modify the reference circuits?

LPP — Fri, 07 May 2021 09:24:26 GMT

The original design was optimized to provide flat gain curve over the target frequency range 87.5-108MHz. It was achieved by matching output load at the upper frequency bound and tuning input matching at lower frequency. See the simulated input/output return loss curve in these graphs:

I modified design to match input impedance at lower bound of your frequency range and left output matching unchanged:

Increasing (!) inductance will reduce frequency cutoff. This inductance compensates reactance of input capacitance of the transistor at the target frequency.

Note, further increasing the inductance will worsen gain flatness over the frequency band.

Regards,
Pavel
NXP CAS