Re: [Discuss-gnuradio] An analog RF question

[address@hidden]

On Sun, 20 May 2018 20:54:34 -0400
"Marcus D. Leech" <address@hidden> wrote:

> Does anyone here know how various high-integration tuners achieve 
> more-or-less continuously-variable corner low-pass frequency on the
> baseband outputs?
> 
> I'm aware of switched-capacitor filters, but my understanding is that 
> due to the high branch ratios, you need a clock with a very high ratio
>    relative to the corner frequency (like 50:1 or 100:1), and so
> doing these for RF/IF filters isn't that practical.
> 
> Another approach is to have a little matrix of Ls and Cs and Rs, and 
> switch different ones in to get a tailored response.  But again, CMOS
> chips aren't that good at producing Ls and Cs of significant value.
> 
> Inquiring minds want to know....
> 
> -Marcus
> 

Can you be more specific about the corner frequency?

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.