Electronic Design
Versatile DCRx Fits Almost Any Radio Application

Versatile DCRx Fits Almost Any Radio Application

All radios used to be superheterodyne radios with downconversion to an intermediate frequency (IF) for filtering before demodulation. While the superhet hasn’t disappeared completely, the direct-conversion zero-IF receiver has mostly replaced it. In fact, most receiver ICs today are direct-conversion ICs.

For example, the versatile CML Microcircuits CMX994 direct-conversion receiver IC (DCRx) fits an incredible array of applications, including the next generation of multi-mode software defined radios (SDRs) for wireless data and two-way radio applications (see the figure). Its design and small size allow a small RF receiver to be realized with a minimum of external components in both zero-IF and low-IF systems.

A DCRx mixes the wanted RF signal down to 0 Hz in a single quadrature mixing process using a local oscillator (LO) tuned to the desired RF operating frequency. Selectivity filtering and gain takes place at baseband with practical, low-power analogue and digital circuits. A DCRx also eliminates the need for an image-reject filter.

The CMX994 offers an on-chip phase-locked loop (PLL) with a voltage-controlled oscillator (VCO) for VHF applications, an operating range of 100 MHz to 600 MHz, precision baseband filtering with selectable bandwidths, and a very small printed-circuit board (PCB) footprint. Also, its single-ended RF antenna connections mean no baluns are required before the low-noise amplifier (LNA). The receiver outputs are the I and Q signals needed by the baseband circuits for demodulation.

Direct conversion’s small size and flexibility make it a key element for the next generation of multi-mode SDRs for wireless data and digital two-way radio applications. Specific applications include multi-mode radios, data telemetry modems, and satellite and land mobile radio systems with 25-, 12.5-, and 6.25-kHz bandwidths.

Available now, the CMX994 operates from 3.0 to 3.6 V. It comes in a Q4 40-pin very thin quad flat no-lead (VQFN) package.

CML Microcircuits

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