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nadroit

Junior Member

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Direct conversion mixer design
Sep 17^th, 2009, 1:21pm

I am designing a direct conversion mixer with RF=L0=2GHz. Thus IF=0Hz. When I simulate it using spectreRF gain at 0Hz (RF-LO) and gain at 4GHz (RF+LO). Gain at 0Hz is less than that at 4GHz. I tried PSS+PAc,PSS+PXF to find gain. Is anything wrong in my understanding of direct conversion mixer? can direct conversion mixer have 0IF or it has some low IF? or is this a simulation problem? please let me know

Thanks

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aaron_do

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Re: Direct conversion mixer design
Reply #1 - Sep 17^th, 2009, 8:32pm

Hi,

the signal that you receive is some signal with a certain bandwidth, called the transmission bandwidth (BT). Therefore, when you down-convert the signal to zero-IF, you are not really looking at the output at 0 Hz, you are looking at the output from 0 Hz to BT/2 Hz. In fact there is a lower limit of the bandwidth too. The IF is a carrier frequency. Zero IF simply means that there is no carrier.

I'm not sure if i understood the question properly, so sorry if I misunderstood.

cheers,
Aaron

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nadroit Junior Member Offline Posts: 14	Re: Direct conversion mixer design Reply #2 - Sep 17^th, 2009, 9:04pm thanks Aaron for ur reply. I understand that its not 0Hz frequency only and I should look at particular bandwidth. But lets say I am just designing mixer for one frequency or in other words bandwidth is zero. So what I want to ask is does zero IF mixer has 0Hz as IF or it has certain IF (say few MHz)? Thanks again.
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currant

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Posts: 31

Re: Direct conversion mixer design
Reply #3 - Sep 17^th, 2009, 11:21pm

Hi,
As I understand, IF=0Hz in zero-IF recievers. May be You have some problems with DC? I think, You could test mixer with input frequency slightly different than LO.
One comment, in zero-IF recievers we have to use I/Q mixer! If You use only one chanel (I or Q) the DC gain could be almost 0 because of phase difference of RF and LO.

Best regards.

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ACWWong Community Fellow Offline Posts: 539 Oxford, UK	Re: Direct conversion mixer design Reply #4 - Sep 18^th, 2009, 10:16am also since you want small signal gain in spectreRF, RF source should be dc and not at 2GHz or any other frequency.
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