Engineering:Low IF receiver

From HandWiki
Jump to: navigation, search

In a low-IF receiver, the RF signal is mixed down to a non-zero low or moderate intermediate frequency, typically a few megahertz (for TV), and even lower frequencies (typically 120-130kHz) in the case of FM radio band receivers. Low-IF receiver topologies have many of the desirable properties of zero-IF architectures, but avoid the DC offset and 1/f noise problems.

The use of a non-zero IF re-introduces the image issue. However, when there are relatively relaxed image and neighbouring channel rejection requirements they can be satisfied by carefully designed low-IF receivers. Image signal and unwanted blockers can be rejected by quadrature downconversion (complex mixing) and subsequent filtering.

This technique is now widely used in the tiny FM receivers incorporated into MP3 players and mobile phones and is becoming commonplace in both analog and digital TV receiver designs. Using advanced analog- and digital signal processing techniques, cheap, high quality receivers using no resonant circuits at all are now possible.