complex filter design

complex filter

Hi friends, I'm trying to do GPS front-end simulation by using ADS, but I don't know how to construct the complex filter module. There're only options for real filters. Could you please help me solve this problem? Thank you

What do you mean by "complex filter"? What is your filter requirement or specs?

ads simulations for gm-c filters

Hello,

you should be aware, that most forum members won't know in detail, how a standard GPS receiver operates, and whether it should, could or could not utilize what you call complex filters, although they are probably motivated to help you and also to learn about the problem.

Personally, I have some knowledge of digital receiver techniques, e. g. knowing that a GPS receiver would use vectorial respectively complex signals in some parts, but didn't remember particularly functions that should be called "complex filters".

Thus I would appreciate some literature reference, a simple schematic, whatever, that illustrates the background of your question.

Regards,
Frank

complex filter equation

Thank you very much, guys.
Complex filter, also called polyphase filter, is used to reject image noise and signal in low-IF architecture. There're many choices of image rejection, like Hartley architecture, Weaver architecture, passive RC polyphase filter and active polyphase filter. Active polyphase filter is preferable among all of them.
A first-order complex filter (bandpass) has the transfer function T(s)=1/(s+1-j) which can be obtained from that of the first-order real lowpass filter (1/(s+1)) by replacing s with s-j.
Here is a literature reference in the attachment.
I'm trying to do the front-end simulation by using the modules provided in ADS (LNA MIXER FILTER). But I don't know how to construct a complex filter in ADS. Are there any other simulation tools suitable for this situation?
Thank you

what is complex filter

Hello,

I expected something like that. I didn't yet know "complex filters" as a common term in signal processing, but that doesn't mean a thing. Polyphase, however, is wellknown and certainly not a synonymous. But no need to discuss term definitions.

The "complex" aspect of the filter is, that it joins two channels, who together represent a complex signal, the wellknown I and Q channels of a receiver. In the receiver, both signals are scalars, and treated as such. In an analog receiver circuit, they are voltages or currents, in a digital one, they are numbers. I don't see any special simulation issue. Complex arithmetics could be needed for the filter design, but not for simulation, I think.

Regards,
Frank

how to design a complex filter from a real filter

VSWR said:

What do you mean by "complex filter"? What is your filter requirement or specs?

Click to expand...

Complex filter is designed to rejecte the image frequency.
It is usually design by active RC or GM-C filter.
I even design a 6th order GM-C cmplex filter to rejecte the image frequecny about 30dB.

Added after 5 minutes:

GM-C compex filter

complex filter both image and rf

thanks it's very useful information

what is complex filter design

I think rfcmosmh need to post this question in digital section as he talks about T(s)=1/(s+1-j).