The whip or pole car antennas of the past have all but disappeared in the latest models. Car designers simply won’t use them anymore because of esthetics as well as wind noise and drag issues. These retro antennas have almost universally been replaced by antenna elements integrated into the rear or side windows or sometimes in the side or rearview mirrors. In most cases the antenna conductor pattern uses the same conductors as the rear window heater and defogger. But these antennas have created a whole new set of design problems.
Atmel’s ATR4253 effectively solves these problems. This car radio IC incorporates all the circuitry needed by a modern embedded antenna. Designed especially for FM radio antennas, it’s a subset of Atmel’s ATR4252 (see the figure), which has similar features but includes AM radio circuitry as well. It consists of an FM signal amplifier, automatic gain control (AGC), integrated dc supply regulator with overvoltage detection, and automatic antenna detection circuitry. The AGC powers an external PIN diode attenuator for managing both high-level and low-level signals.
Designed to be mounted close to the antenna, the chip provides pre-amplification to offset noise prior to the connection to the radio front end. It also provides for impedance matching to the antenna, which is critical for best performance. Additionally, the IC can accommodate dual-phase diversity antennas, which are a popular trend in FM radio antenna design.
The ATR4253 offers wide frequency coverage from 60 to 790 MHz and can handle all standard FM radio bands in the world. This wide frequency range also enables the IC to work with newer digital radios and TV devices, such as DAB/DAB+/DMB digital radio in Europe and Korea, DVB-T digital TV in Europe, and ISDB-T digital TV in Japan. Its amplifier performance is excellent with a 1.6-dB noise figure and a linearity spec of FM output third-order intercept point (OIP3) of 145 dBµV.
The ATR4253 is made with biCMOS and comes in a 3- by 3-mm QFN16 package. It is good for ambient temperatures up to 115°C. Pricing starts at $0.69 in 100,000-unit quantities. Demo boards and evaluation kits are available.