Product Releases

IF Digitizing IC

Mon, 01/14/2002 - 4:09am
Analog Devices, Inc., announced a new IF (intermediate frequency) digitizing IC designed for radios that must meet the highest standards of reliability and performance. Private mobile radios used by police, fire and ambulance services, as well as narrowband communications systems for fleet management of taxis and delivery services, rely on radio receivers that can detect weak signals in the presence of large interference. The new AD9874 integrates the IF-to-digital conversion process onto a single chip that can be used to design a highly-sensitive, very low-power receiver suitable for a range of equipment, including dispatcher base stations, handheld portable radios and in-vehicle consoles.

The AD9874 is a member of the company's Mixed-Signal Front End (MxFE™) family, and is based on ADI's "smart partitioning" methodology — a mixed-signal design technique that partitions the signal path according to performance-enhancing, rather than analog/digital boundaries. The AD9874 MxFE integrates all the functional blocks (excluding the LO and VCO) needed for IF-to-digital conversion in a narrowband superheterodyne receiver. This partitioning reduces IF filtering, enhances demodulation accuracy and delegates all modulation-specific functions to an external digital signal processor.

The AD9874 MxFE digitizes low level IF signals from 10 to 300 MHz with a bandwidth of up to 270 kHz. Typical noise figure is 8.7 dB SSB NF and linearity, as measured by third-order input intercept point (IIP3), is +0 dBm IIP3 (typical maximum bias). The AD9874 is notable for its power efficiency, 21.2 milliAmps versus 45 milliAmps for previous generations. The signal chain consists of a low noise amplifier, a mixer, a bandpass sigma-delta analog-to-digital converter, filters and automatic gain control (AGC) circuitry capable of 12 dB continuous gain adjustment. The high dynamic range and inherent anti-aliasing provided by the bandpass sigma-delta converter allow the AD9874 to cope with blocking signals 80 dB stronger than the desired signal. The AD9874 is fully programmable, providing register-based digital control of AGC and filter parameters, amplifier gain and bias currents through a serial peripheral interface (SPI) port.


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