[Moved]: Design of polyphase filters

[Vishnudas Thaniel S]

Hi all,
I am designing a polyphase filter for a receiver section. I have read some materials and got some idea and designed it in cadence. The circuit diagram is attached with this. But I do not know how to test it and see whether it is working or not. I am unable to see whether image rejection is taking place or not. The WoC block is a low pass filter with cut off frequency of 2MHz and W_IF block is a low pass filter of cut off frequency 1MHz. My IF frequency required is around 2MHz. Each block was realized using Nauta based Operational Transconductance Amplifier. Please tell me whether what I have desigened is correct or not. I also want to know what all analyses are to be performed on this and how to do them.

 

[LvW]

Re: Design of polyphase filters

I would recommend the following tests (simulation):
1) AC analysis using the two input signals with the nominal phase shift of +90 deg (Xin=Xi+jQ). As desired, this should result in a symmetric bandpass function.
2.) AC analysis using the input signals with a complemetary phase shift (Xin=Xi-jQ). This should show the image rejection (damping properties).

 

[Vishnudas Thaniel S]

Hi, thanks for the reply.
I did like what you said. I gave a sinusoid at one input and with 10mV amplitude and 2MHz frequency with an initial phase of 0 .Then another sinusoid was given at another input with same frequency and 5mV amplitude and with a phase of 90. Then I did AC analysis with frquency varying from 1MHz to 10MHz. The I and Q outputs obtained are attached with this. Then I did the same analysis with 0 and -90 as phase for both signals without varying any other parameters. But I am getting the same output which is also attached. Kindly help me with this.

 

[LvW]

Why don`t you use two equal frequencies (same amplitudes) with a phase shift of (+-) 90 deg?