What Is a Superheterodyne Receiver?

A superheterodyne receiver is a method of mixing a locally generated oscillation wave with an input signal to transform the frequency of the input signal into a predetermined frequency. The superheterodyne principle was first proposed by EH Armstrong in 1918. This method is developed based on the principle of heterodyne in order to meet the needs of high-frequency and weak signal reception in remote communications. The heterodyne method is to convert the input signal frequency to audio, and Armstrong's method is to convert the input signal to super audio, so it is called super heterodyne. In 1919, the superheterodyne receiver was made using the principle of superheterodyne. The performance of this receiving method is superior to high-frequency (direct) amplification receiving, so it is still widely used in remote signal reception, and has been applied to measurement technology and other aspects.

The superheterodyne principle was first proposed by EH Armstrong in 1918. It is developed on the basis of the principle of heterodyne. The heterodyne method is to convert the frequency of the input signal into audio, and the superheterodyne method proposed by Armstrong is to convert the frequency of the input signal to super audio, so it is called superheterodyne . In 1919, the superheterodyne receiver was made using the principle of superheterodyne, which is still widely used in remote signal reception, and has been applied to measurement technology and other aspects. The superheterodyne receiver effectively solves the problems of weak output and poor stability of the original high-frequency amplified receiver, and the output signal has high selectivity and good frequency characteristics, and is easy to adjust. At the same time, superheterodyne receivers also have complex circuits and problems such as image frequency, combined frequency, and intermediate frequency interference. With the development of digital signal technology, the main methods to solve these problems are to improve the selectivity of high-frequency amplifiers and adopt a second-frequency conversion method ^[1]

The input signal of the receiver is often very weak (typically several microvolts to several hundred microvolts), and

The super heterodyne receiver has a large receiving dynamic range; the second is a high adjacent channel selectivity and receiving sensitivity. In order to suppress strong interference and make it have good selectivity, generally a pre-selected RF filter and an IF filter can be installed in front of and behind the mixer, respectively. Third, it is less affected by the imbalance of the I / Q signal. Therefore, no complicated DC elimination circuit is needed. Fourth, because it generally uses one or more intermediate frequency mixing, the circuit will be more complicated and costly, and the integration is not high. Fifth, it will use a lot of expensive , Larger SAW or ceramic discrete filters; Six is generally higher

With the development of integrated circuit technology, superheterodyne receivers can be integrated on a single chip. For example, there is a monolithic AM-FM receiver. Its AM / FM high-frequency amplifier, local oscillator, mixer, AM / FM intermediate frequency amplifier, AM / FM detector, and audio power amplifier. And automatic gain control (AGC), automatic frequency control (AFC), tuning instruction circuit (700 components in total) are integrated on a chip with an area of 2.4 × 3.1 mm, and its operating voltage range is 1.8-9 volts The quiescent currents for the AM and FM modes are 3 mA and 5 mA, respectively. ^[2]