Wireless Infrastructure: Heterodyne RX/TX

In the single-IF Heterodyne configurations, a digital up converter (DUC)/down converter (DDC) replaces the IF analog modulator/demodulator, which means no LO/carrier self-mixing at IF to obtain perfect gain/phase matching. Carrier/channel selection can be implemented in the digital domain (DUC/DDC). The single channel ADC/DAC does not receive/transmit a low frequency baseband signal, but an intermediate frequency (IF). The IF is defined by the frequency of the digital sine and cosine generator, which is a numerically controlled oscillator (NCO). The IF signal is up/down converted to/from RF through one analog mixing stage, reducing the RF BOM. The IF frequency is usually in the 70 MHz to 200 MHz range.

Benefits

No LO/carrier self-mixing at IF, perfect gain/phase matching, no offset.

High IF relaxes RF front-end image rejection filter requirement.

Reduces RF BOM (Bill of Materials).

Tradeoffs

High IF requires a wideband data converter, but ADC/DAC performance at such a high IF range limits the performance of such an architecture.

Carrier/channel selection can be implemented in the digital domain (DUC/DDC) but requires a high speed ADC/DAC.

• All Data Converters Block Diagrams