Hey Marcus, This may not be what you are looking for, but these are awesome. They may be going to space soon :) http://www.newedges2.com/products/SAX239-R2_Datasheet_February-27th-2018.pdf
On Sun, May 20, 2018 at 10:13 PM li...@lazygranch.com <li...@lazygranch.com> wrote: > I used to work at Maxim, but my dealings with those RF guys dealt more > with coffee and the quality thereof. > > I looked at the Maxim chip. The filter is relatively steep but not > complex. Looks like two or three poles maximum. I don't know > specifically about that chip, but that group had SiGe technology, so > I'm leaning towards variable transconductance to do the tuning. > > You quickly learn just how bad google is at doing a search for this > technology. The buzz phrase you need is continuous time, so I suggest > "variable continuous time baseband filter". Sadly OTA gets links to > "over the air." (And yet, they claim artificial intelligence will take > over the world.) > > The thing to note in any highly integrated analog chip is that you > don't see the sausage being made. Once you have a system on a chip, the > metric is the system performance, not the performance per se of any > individual block. So those filters may not be as great as you think. > Note the Maxim part shows a tempco on the corner frequency, which could > imply variable transconductance. One you have bipolar elements in the > process, variable transconductance is just a matter of tail current. > (SCF performance was relatively temperature independent.) > > Getting back to seeing the sausage, take the old analog modem market. > Initially the SCF tech was used to make the official Bell 212 filters. > Once the modem was fully integrated, the on-board filters were > simplified for a number of really good engineering reasons, not just > cost. One was the harmonic distortion of the band split filters. The > harmonics of the in-band signal were far greater than the out-band > signal that you were trying to reduce. > > Getting back to these baseband filters, if you use a ladder design, the > filter is relatively immune to component error, well as opposed > (contrasted) to a chain of biquads. If you go full differential, the > variable transconductance amp are reasonably linear. But probably they > limit the number of poles for the same harmonic distortion problem. > Filters should subtract, not add. > > Most of the transconductance based filter designs probably are > derivatives of integrated video filters. Plenty of papers online for > those designs. > > If your goal is to roll together your own filter, TI has app notes on > how to make analog tracking filters. > > On Sun, 20 May 2018 21:19:47 > -0400 "Marcus D. Leech" <mle...@ripnet.com> wrote: > > > On 05/20/2018 09:13 PM, li...@lazygranch.com wrote: > > > > > > Can you be more specific about the corner frequency? > > Corner frequencies step-tunable from perhaps 20Mhz down to perhaps > > 2MHz. > > > > Many chips, like the R820T2, the MAX2112, and the higher-integration > > devices like the AD9361 and LMS7002M have > > programmable analog low-pass corner frequencies, for bandwidth > > tailoring of the complex baseband. > > > > Just not sure how its done. The chips have very low external parts > > count, so whatever it is, it's got to be done > > internally... > > > > > > > > > > Cell phones use chips that have switchable banks of capacitors for > > > antenna tuning. st.com IIRC is a source. > > > > > > I used to design switched capacitor filter chips in the 80/90s. The > > > technology was killed by oversampled converters and DSP. The SCF > > > players went into continuous time video filters using > > > transconductance amps and such. > > > > > > > > > _______________________________________________ > > > Discuss-gnuradio mailing list > > > Discuss-gnuradio@gnu.org > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > -- Very Respectfully, Dan CaJacob
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