This article discusses how to optimize performance by minimizing IM2 nonlinearity and DC offset that reduce the dynamic range of zero-IF receivers, thus offering a viable alternative to an otherwise challenging design.
The document addresses the challenges of designing high-performance wireless base stations that support wider bandwidths (up to 300MHz) required for 4G networks. It highlights limitations in traditional high-IF receivers regarding sampling rates, gain flatness, and cost. The text introduces the LTC5585 IQ demodulator as a solution designed to support direct conversion of wide RF signals directly to baseband.
| -3dB corner frequency requirement | well above 500MHz |
|---|---|
| Differential I and Q output ports pull-up resistance | 100Ω |
| Filter capacitance for baseband output stage | about 6pF |
| -3dB bandwidth with 100Ω differential output loading resistance | 850MHz |
The LTC5585 has the unique ability to adjust for minimum IM2 spurs independently on the I and Q channels by using external control voltages.
Zero-IF demodulation produces no image at the baseband, thus eliminating the need for a relatively expensive SAW filter.