Information about designing image filters

Hi all,

Do anyone know about image filter? How to design the image filter?
Do anyone can share these articles or books?

I search a couple of days in Internet, but cannot find the related information.

Thanks in advance!

In general an image filter is a standard Band Pass Filter.
Because the duty of the image filter is not only to filter the image frequency and also reducing the image noise, the bandwidth of this filter shall be equal with the RX bandwidth. The out of band rejection of the image filter is given by the RF system analysis.

You also need to consider filter's insertion loss and in-band ripple, matching and group delay.

i agree with RF-OM and Vfone . u need to take care about this filter coz sometimes u will need it very high Q coz the BW is usuallay low.

the attenuation of the filter will depend image rejection ratio

Khouly

Thanks for all valuable informations. That means to design image filter is similiar to design filter using Butterworth, Chebyshev or Bessel topologies. Just different is their duty only. Am I right?

How we consider the group delay? How important with this concerns?

Thanks.

The image filter usually is band pass filter and must be designed with the spec obtained from RF System Design process. In general it is just ordinary filter, but sometimes it may be something more exotic like multiple notches or resonance filters or filters with pads in order to optimize mixer termination (in this case it is necessary to keep in mind that thermal noise at the image frequency will be restored after filter). One more point: the image filter usually installed after the LNA and serve not only for image rejection but also for attenuation of products generated into LNA and improving the total system linearity.

Group delay is a kind of different parameter because it is not natural, but artificial. It is the measure of how dispersive the filter is. Actually it is important mostly for digital communications because it increase the ISI. More important not the absolute value of S21GD, but rather its variations. Historically it goes from old wired multichannel communication systems when channels were combined into groups. The first 12 channels were called the primary group. Then 5 such primary groups created the secondary 60 channels group, then 5 secondary groups combined to the tertiary 300 channels group and so on. When there are a lot of channels and groups the occupied spectrum become wide and signals from different groups arrive to the end station with different delay. From this phenomenon term group delay was derived. Mathematically it is slope of the phase response and related to the speed of energy transfer through the system. For today's communication engineering the group delay parameter is one the most important and must be carefully considered at the time of design process.

oic, now i am clear with it.

Do you have any articles or books recommended regarding with Image Filter?

Thanks.

Image filter design process is the same as for other filters, so for this you need to check filter design papers and books. But before starting filter design you need to have specification. It goes from detailed RF System design and analyzes. This is different area. For both of these fields there are a lot of books and papers. You need to find which will be the best for considering what you know, what you want to learn and what should be done in the end. If you are new in the filter design probably Randal Rhea's book: "High Frequency Filter Design and Computer Simulation" will be good for start. There you also find good lists of references.