We are interested in interfacing the LMS6002D device which provides Zero-IF ADC interface to a Low-IF ADC or Standard-IF ADC interface. This will need a complex filter to be designed to suppress the images and passing the filtered/computed I-component to the ADC interface. Can you point me to any such circuit which is available ? We would like to interface the Tuner Output from LMS6002D to our Demodulator chip which has a differential I-interface only.
Anindya,
This requires more clarification. Do you want to use in your application LMS6002D RX analog outputs only? What is your IF BW requirements?
Rich
Yes, we want to use the LMS6002D’s RX analog outputs only. The Low IF BW requirement is between 6-8Mhz. We want to use the RX as pure Low-IF receiver (which it is not). Hence we would choose the LO frequency so that it is offset by a few Mhz from DC and using the capabilities of the RX LPF will extract the required 6-8Mhz. Since there is an image foldover which will happen we will insert complex filters to remove them before the I-component of the signal enters the ADC.
I this case you would need to use RF filter rather then in IF filter. Because, when the signal passes through the mixer you would not be able filter the image, even then if you use the IF Filter.
Your bandpass filter should have 6 - B MHz bandwidth on your wanted frequency and required rejection ratio on your image band.
Rich
I am not sure what type of RF filter one would use, since we do not want to develop band specific filters. The images coming after mixing can indeed be removed if the right filters are used. The NXP tuner like TDA18275 which are truly Low-IF work on this principle.
-best regards
Anindya Saha