As the recent report from the FCC Laboratory on Interference Rejection Thresholds of Consumer Digital Television Receivers shows, single conversion DTV receivers remain somewhat susceptible to taboo channel interference. Interference can be caused by signals mixing in the receiver to create interference on the IF (intermediate frequency) used in most DTV tuners. Maxim Integrated Products last week said such interference could be eliminated with a new zero-IF tuner for digital terrestrial TV by converting the incoming RF directly to baseband instead of an intermediate frequency.
Maxim said its new MAX3580 fully integrated, zero-IF, direct conversion DTV tuner includes an RF-tracking filter that eliminates the need for external, discrete filtering components and the expensive SAW (surface acoustic wave) filter required by older IF-based tuners. While the company said the MAX3580 was designed for DVB-T applications using an 8-MHz wide channel, I don't see why a similar design wouldn't work for a 6-MHz wide ATSC channel. The MAX3580 data sheet shows adjacent channel (N+/-1) rejection at a minimum of 29 dB, typically 40 dB. Second adjacent channel (N+/-2) rejection was specified as 40 dB minimum, typically 43 dB. Linearity/crossmod specifications with N+/-2 and N+4 channels was 40 dB minimum and 47 dB typical. NorDig 16QAM sensitivity was -84.1 dBm minimum, typically -85.1 dBm.
The tuner consumes only 650 mW of power, making it suitable for USB stick and automotive applications. It operates from a single 3.3-volt supply. An evaluation kit and reference designs that combine the MAX3850 with OFDM demodulators are available from Maxim. When will we see an ATSC-compatible version of this chip?
