ATR4251 PDF Datasheet – Antenna Amplifier IC

An impedance matching circuit for an AM/FM antenna is designed to ensure that the antenna’s impedance matches the input impedance of the receiver or the input stage of the radio. This helps maximize the transfer of power from the antenna to the receiver, improving signal reception and reducing signal loss. Impedance matching is particularly important in radio frequency (RF) circuits to minimize signal reflections and optimize signal strength.

Part Number: ATR4251

Function: High-dynamic-range Antenna Amplifier IC

Package: SSOP 20 Pin Type

Manufacturer: ATMEL Corporation


1 page
ATR4251 pdf datasheet


The ATR4251 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
(150 kHz to 30 MHz) that are usually used for AM transmission, and FM means any of the frequency bands used world-wide for FM radio broadcast (70 MHz to 110 MHz).



1. High Dynamic Range for AM and FM

2. Integrated AGC for AM and FM

3. High Intercept Point 3rd Order for FM

4. FM Amplifier Adjustable to Various Cable Impedances

5. High Intercept Point 2nd and 3rd Order for AM

6. Low Noise Output Voltage

7. Low Power Consumption

8. Low Output Impedance AM


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ATR4251 pinout

AM Amplifier

Due to the long wavelength in AM bands, the antennas used for AM reception in automotive
applications must be short compared to the wavelength. Therefore these antennas do not provide 50Ω output impedance, but have an output impedance of some pF. If these (passive)
antennas are connected to the car radio by a long cable, the capacitive load of this cable (some
100 pF) dramatically reduces the signal level at the tuner input.


ATR4251 PDF Datasheet

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