How to design a LPF that its -3dB frequency variation over PVT can be less than 20%

[pz5921087]

Hello,
I am designing a LPF which needs to achieve 50MHz with 20% accuracy(range 40MHz to 60MHz). The poly res and MIM cap all have ~20% variation over PVT, it is really hard to design such a LPF with simple RC. Can anybody suggests a circuit topology that can realize this LPF? Thank you very much!

 

[dick_freebird]

I guess you'd have to start with a technology that has better
than 10% capacitor and 10% resistor tolerances (or, if a gm-C
type, you would have to design a bias network that keeps gm
similarly tight.

That is to say, good luck. I've run across no resistors with
that kind of "make" tolerance, and many whose tempco would
blow the deal even if 0% initial.

You could of course trim capacitances and resistors / bias.

You might consider switched capacitor type filters where
the passband is set by clock rate. If you can expect to be
provided a clock to your liking.

 

[D.A.(Tony)Stewart]

Hello,
I am designing a LPF which needs to achieve 50MHz with 20% accuracy(range 40MHz to 60MHz). The poly res and MIM cap all have ~20% variation over PVT, it is really hard to design such a LPF with simple RC. Can anybody suggests a circuit topology that can realize this LPF? Thank you very much!

If you must have film, consider AVX Accu-F/Accu-P Film caps 5% 25V 805 case , $1k per 3k reel. not always in stock.

TEMP. COEFFICIENT CODE “J” = 0±30ppm/°C (-55°C to +125°C)
Accu-F® Signal Type Capacitors
TEMP. COEFFICIENT CODE “K” = 0±60ppm/°

You can also pay for pre-sorted caps tested by Distributors. I've also done this for clients with 1% bins for Poly caps.

With more precision requirements and complex BPF + Band Reject types, custom MLCC filters on ceramic are common in volume and higher frequency.

Usually one just uses COG/NP0 ceramic caps like Murata GRM1555C1H series $22 per 10k reel. 5% tolerance.

 

[LvW]

Hello,
I am designing a LPF which needs to achieve 50MHz with 20% accuracy(range 40MHz to 60MHz). The poly res and MIM cap all have ~20% variation over PVT, it is really hard to design such a LPF with simple RC. Can anybody suggests a circuit topology that can realize this LPF? Thank you very much!

No other specification? Which order?