The Atmel? ATR4251C is an integrated low-noise AM/FM antenna amplifier with integrated AGC in BiCMOS2S technology. The device is designed in particular for car applications， and is suitable for windshield and roof antennas.

　　The Atmel? ATR4251C is an integrated AM/FM antenna impedance matching circuit. It compensates cable losses between the antenna （for example windshield， roof， or bumper antennas） and the car radio which is usually placed far away from the antenna. AM refers to the long wave （LW）， medium wave （MW） and short wave （SW） frequency bands （150kHz to 30MHz） that are usually used for AM transmission， and FM means any of the frequency bands used world-wide for FM radio broadcast （70MHz to 110MHz）。 Two separate amplifiers are used for AM and FM due to the different operating frequencies and requirements in the AM and FM band. This allows the use of separate antennas （for example， windshield antennas） for AM and FM. Of course， both amplifiers can also be connected to one antenna （for example， the roof antenna）。 Both amplifiers have automatic gain control （AGC） circuits in order to avoid overdriving the amplifiers under large-signal conditions. The two separate AGC circuits prevent strong AM signals from blocking FM stations， and vice versa.