IF Amplifier

In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency. Intermediate frequencies are used in superheterodyne radio receivers, in which an incoming signal is shifted to an IF for amplification before final detection is done.

IF amplifiers can change the frequency levels in circuits that are too selective, difficult to tune, and unstable. They also help by changing the frequency levels in circuits which improve image display and tuning range. They are fixed frequency amplifiers which reject unwanted signals.

IF amplifiers are implemented as amplifying circuits in radio-frequency (RF) receivers that process and enhance a down converted or modulated signal. Signal frequency spectrum down conversion is achieved by multiplying the radio-frequency signal by a local oscillator signal in a circuit known as a mixer. This multiplication produces two signals whose frequency content lies about the sum and difference frequencies of the center frequency of the original signal and the oscillator frequency. A variable local oscillator is used in the receiver to hold the difference-signal center frequency constant as the receiver is tuned. The constant frequency of the down converted signal is called the intermediate frequency (IF), and it is this signal that is processed by the intermediate-frequency amplifier.