What is high frequency with RF? What's the difference between them? When it comes to the essential difference between high frequency and radio frequency, it is only the working environment. But which specific parameters are different, please and RenhotecIC through the following to understand, but also to expand our technical level!


　　1、Initial High Frequency Circuit

　　The high frequency circuit of high frequency circuit is basically composed of passive device, active device and passive network. The passive linear elements in high frequency circuits are mainly resistors, capacitors and inductors (devices). High frequency circuits, to put it bluntly, are radio circuits, but do not involve microwave circuits (microwave is used to process circuits above 1,000 MHz, starting with physical electromagnetic fields, very different from our common circuits), for radio wave transmission, reception, modulation, demodulation, amplification, and so on.

　　2、Performance Index of High Frequency Circuit

　　High frequency small signal amplifier has two circuit forms: resonant amplification and broadband amplification. The performance indexes mainly include the following items.

　　(1) Gain

　　High-frequency circuits, like low-frequency circuits, have indicators of voltage gain and power gain. For a resonant amplifier circuit, it means at the resonant frequency f0, for a broadband amplifier circuit, it means at a certain frequency bubble.

　　(2) Pass band

　　Similar to the concept of low-frequency circuits, for resonant amplifier circuits, the passband refers to the difference between the two corresponding frequencies at which the normalized amplitude drops to 0.707 relative to the resonant frequency f0; for broadband amplifier circuits, it is relative to a certain frequency. definition.

　　(3) Selectivity

　　The selectivity is mainly aimed at the resonant amplifier circuit, which characterizes the ability of the circuit to select useful signals to suppress useless signals. It is usually measured by the rectangular coefficient and the suppression ratio, which are based on the resonance characteristic curve of the circuit.


　　(4) Noise figure

　　When the amplifying circuit is working, the irregular movement of carriers will occur due to various reasons, and noise will be formed inside the circuit, which will affect the signal quality. This effect is usually described by the ratio of signal power Ps to noise power Pn (referred to as signal-to-noise ratio). The noise figure is defined as the ratio of the input signal-to-noise ratio to the output signal-to-noise ratio.

　　(5) Stability

　　The stability of a high-frequency amplifier circuit refers to the degree of stability of its main performance when the working state or conditions change. For example, changes in ambient temperature or fluctuations in power supply voltage will affect the DC working state of the amplifying circuit; circuit component parameters will also change, leading to changes in the gain of the amplifying circuit, center frequency shift, and resonance curve distortion. Even self-excited and completely unable to work.

　　3、Grounding Principle of High Frequency Circuit

　　For circuits and digital circuits with high working frequency, because the lead of each component and the inductance of the circuit layout itself will increase the impedance of the ground wire, the single point grounding method is widely used in low frequency circuits. If used in high frequency circuit, it is easy to increase the impedance of ground wire, and the stray inductance and distributed capacitance of ground wire will also cause the coupling between circuits, thus making the circuit work unstable.


　　In order to reduce the impedance of ground wire and reduce the stray inductance and distributed capacitance between ground wires, the coupling between circuits is caused. High frequency circuit adopts the principle of nearest grounding, that is, multi-point grounding, and connects the system ground wire of each circuit to the low impedance ground wire. Generally speaking, when the working frequency of the circuit is higher than 10 MHz, the multi-point grounding method should be adopted. Because the grounding key of high frequency circuit is to reduce the stray inductance and distributed capacitance of ground wire as far as possible, there is a great difference between the grounding implementation method and the low frequency circuit.

　　4、Introduction to Radio Frequency Circuit

　　Radio frequency (RF) is the abbreviation of Radio Frequency, representing the frequency of electromagnetic waves that can be radiated into space, ranging from 300 kHz~300 GHz. Radio frequency is radio frequency current, it is a kind of high frequency AC change electromagnetic wave abbreviation. Ac electricity with a change of less than 1000 times per second is called low frequency current, and more than 10000 times is called high frequency current, and radio frequency is such a high frequency current. Radio frequency (300 K-300G) is the higher frequency band of high frequency (more than 10 K), and microwave band (300 M-300G) is the higher frequency band of radio frequency.


　　In the theory of electronics, the current flows through the conductor, and a magnetic field will be formed around the conductor; the alternating current will pass through the conductor, and the alternating electromagnetic field will be formed around the conductor, which is called electromagnetic wave.

　　When the electromagnetic wave frequency is less than 100 khz, the electromagnetic wave will be absorbed by the surface and can not form an effective transmission, but when the electromagnetic wave frequency is higher than 100 khz, the electromagnetic wave can propagate in the air and reflect through the ionosphere of the outer edge of the atmosphere.

　　5、Composition and Characteristics of RF Circuit

　　The radio frequency circuit of ordinary mobile phone consists of three circuits: receiving path, transmitting path and local oscillator circuit. It is mainly responsible for receiving signal demodulation; transmitting information modulation. The early mobile phone demodulates the receiving baseband information through the superheterodyne frequency conversion (the mobile phone has, two mixing and one and two local oscillator circuits), and the new mobile phone demodulates the receiving baseband information directly (zero intermediate frequency). And some phones integrate the frequency-combination and receive voltage-controlled oscillators (RX—VCO) inside the medium frequency.

　　The circuit that can transmit or radiate high frequency electromagnetic wave to the outside world through antenna or RF transmitter is called RF circuit. The characteristic of radio frequency circuit is that it can transmit high frequency electromagnetic wave to the outside world.

　　High frequency circuit is a circuit that can run high frequency signal, receive high frequency signal, or produce high frequency signal, or amplify high frequency signal, transmit high frequency signal, or process high frequency signal. RF circuit is also a kind of high frequency circuit.

　　The above is high frequency and radio frequency analysis, I hope to help you.