Programmable band-pass filters

Hi,
Are there any components that can be used to implement a
programmable band-pass filter between the antenna and the LNA, of the RF
front-end for an SDR application.

I was wondering if there are an discrete components available that can
be programmed by I2C or SPI, that can be controlled by an FPGA, to tune
the band-pass filter in between the antenna and the LNA.

Best regards,

Elvis

On Fri, Jul 9, 2010 at 11:30 AM, Elvis D. [email protected]
wrote:

Hi,
Are there any components that can be used to implement a programmable band-pass filter between the antenna and the LNA, of the RF front-end for an SDR application.

I was wondering if there are an discrete components available that can be programmed by I2C or SPI, that can be controlled by an FPGA, to tune the band-pass filter in between the antenna and the LNA.

You could try something like a switched filter bank as a preselector:

http://www.spectrummicrowave.com/sfb.asp

That was something a quick google search found. Unfortunately, your
band-pass requirements are lacking. What types of channel bandwidths
do you want? How many channels? How much rejection are you looking
for?

I am guessing said filters are pretty expensive.

Best regards,

Elvis

Good luck.

Brian

Hi,

On Jul 9, 2010, at 7:53 PM, Brian P. wrote:

You could try something like a switched filter bank as a preselector:

http://www.spectrummicrowave.com/sfb.asp

I was thinking of a discrete SMT type component, which I can mount on a
PCB board, those are really big.

That was something a quick google search found. Unfortunately, your
band-pass requirements are lacking. What types of channel bandwidths
do you want? How many channels? How much rejection are you looking
for?

I was initially thinking of a BPF in the 400Mhz to 4000Mhz range. This
would interface with a LNA of the same band-width. However, I would like
to be able to digitally control the BPF, to be able to say filter
frequencies, prior to sending it to the LNA, e.g. 1800Mhz to 2200Mhz,
and then switch back to 400 to 600Mhz, etc.

Doing a google search, I came across FPAA (Field Programmable Analog
Arrays), and I was wondering if using a switched bank of capacitors and
resistors, would do the trick?

I found one company http://www.anadigm.com/

haven’t gone into the details of an FPAA, but was wondering if someone
else on this forum has looked into this type of thing before?

Could I potentially create my own externally switched capacitor &
resistor network, under control of a standard FPGA, to achieve the same
thing?

Best regards,

Elvis D.

HI Marcus,

On Jul 9, 2010, at 9:36 PM, Marcus D. Leech wrote:

You should know that any filter you place in front of an LNA needs to have a ridiculously low insertion loss in to not severely degrade the noise figure if the LNA

It’s likely that any switchable filter will have unacceptably high insertion loss

A better approach is to use a first LNA with modest gain and good OIP3 and P1dB then your filters then another low noise stage

The following diagram represent the various stages for a direct
conversion RF front-end.

You should know that any filter you place in front of an LNA needs to
have a ridiculously low insertion loss in to not severely degrade the
noise figure if the LNA

It’s likely that any switchable filter will have unacceptably high
insertion loss

A better approach is to use a first LNA with modest gain and good OIP3
and P1dB then your filters then another low noise stage


Principal Investigator
Shirleys Bay Radio
Astronomy Consortium
http://www.sbrac.org