Direct Conversion-Zero IF question?

I heard DSP argorithm to implemente DC Cancellation in zero-IF Transceiver, who knows this argorithm? where can find it?


thanks.

Hi,
I thought that the method was to use large number of bits ( 8-12) with high dynamic range so that the DC may be removed. If the DC is large to affect the amplifiers .... then this may not be suitable.

brmadhukar

That is an outdate method!

If the offset appears early in the gain path (natural with a ZeroIF mixer) the digital offset correction should have a dynamic range of the signal + offset*gain. More bad news are that the offset could clip some amplifiers in between. Some guys think about feeding back a DAC to the mixer output. It helps a little bit but there are more clever solutions by building mixed gain/offset correction blocks.

How do I know the output of mixer is DC offset or signal? How to distinguish them and seperate them?

Either

1. Use frequency domain filtering if the signal has zero DC like OFDM or Wideband FSK.

2. Disable your signal for the correction

Easy?

Well, not easy for me. Give me a more hits, please.

I think rfsystem means : using a HPF(high pass filter) to filtering DC(frequency =0Hz) , And for the OFDM I am not farmiliar with that but
maybe that's some kinds of architecture defined by OFDM or other scheme?

For wideband FSK you could filter out with a high order highpass filter the normally time varing DC offset. The impact is a small degradation of S/N versus BER trade. Try to optimize the corner frequency and order to you system because the initial settling time of the filter determine the time which you loose in a TDMA packet for synchronisation.

OFDM is similar to wideband FSK because at zero there is no carrier.