Versatile DCRx Fits Almost Any Radio Application

Jan. 31, 2012

Single-chip zero IF receiver covers wide frequency range for SDR applications.

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The CML Microcircuits CMX994 single-chip direct-conversion receiver (DCRx) covers from 100 to 600 MHz. The single-ended RF input eliminates a balun, and the outputs are the I/Q signals to the baseband circuits. An on-board integer-N PLL with VCO sets the operating frequency. It comes in a 40-pin VQFN package.

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
www.cmlmicro.com

About the Author

Lou Frenzel | Technical Contributing Editor

Lou Frenzel is a Contributing Technology Editor for Electronic Design Magazine where he writes articles and the blog Communique and other online material on the wireless, networking, and communications sectors. Lou interviews executives and engineers, attends conferences, and researches multiple areas. Lou has been writing in some capacity for ED since 2000.

Lou has 25+ years experience in the electronics industry as an engineer and manager. He has held VP level positions with Heathkit, McGraw Hill, and has 9 years of college teaching experience. Lou holds a bachelor’s degree from the University of Houston and a master’s degree from the University of Maryland. He is author of 28 books on computer and electronic subjects and lives in Bulverde, TX with his wife Joan. His website is www.loufrenzel.com.