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¡¡¡¡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.