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Introduction of high frequency PCB
high frequency PCB is a radio circuit, but it does not involve microwave circuit (microwave is used to process circuits above 1000 MHz, starting from the electromagnetic field of physics, which is quite different from our common circuits), and is used for radio wave transmission, reception, modulation, demodulation, amplification, etc.
Digital circuits process digital signals, and digital signals only have high and low signals (for example, the working range of digital circuits in CMOS technology is 0-3.3v, 0-0.8v is considered as low level, 2.4-3.3v is considered as high-level level, and other voltages are considered invalid. All electrical signals are divided into high-level and low-level sequences), which are suitable for high-speed processing, high-processing, and computer interface handle.
Analog circuit does not distinguish the level, all the continuous signals are processed together (the macroscopic physical quantities in nature are continuous), which are used for power supply, amplification, filtering and so on.
Analog circuit and high-frequency circuit are very close to each other, but the working frequency of the circuit is high, and the physical characteristics of many components change, so the processing methods and problems are different.
Performance index of high frequency PCB
High frequency small signal amplifier has two kinds of circuit forms: resonant amplifier and broadband amplifier. The performance index mainly includes the following items.
1. Gain
High frequency circuit and low frequency circuit have voltage gain and power gain index. For the resonant amplifier circuit, it refers to the resonant frequency f0, for the broadband amplifier circuit, it refers to a frequency bubble.
2. Passband
Similar to the concept of low-frequency circuit, for resonant amplifier circuit, passband refers to the difference between two corresponding frequencies when the normalized amplitude drops to 0.707 relative to resonant frequency f0; for broadband amplifier circuit, it is the corresponding definition relative to a certain frequency.
3. Selectivity
Selectivity is mainly aimed at resonant amplifier circuit, which characterizes the circuit's ability to select useful signals to suppress useless signals. It is usually measured by rectangular coefficient and suppression ratio, which are based on the resonance characteristic curve of the circuit.
4. Noise figure
When the amplifier circuit works, due to various reasons, the carrier will move irregularly and form noise 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 (SNR). Noise figure is defined as the ratio of input signal to noise ratio and output signal to noise ratio.
5. Stability
The stability of high frequency amplifier circuit refers to the stability of its main performance when the working state or condition changes. For example, the change of the ambient temperature or the fluctuation of the power supply voltage will affect the DC working state of the amplifier circuit; the circuit component parameters will also change, which will cause the gain of the amplifier circuit to change, the center frequency offset, and the resonance curve distortion. Even self-excited and unable to work at all.
Schematic diagram of high frequency circuit
Introduction of RF PCB
Radio frequency is referred to as RF, radio frequency is the radio frequency current, it is a kind of high frequency alternating current electromagnetic wave abbreviation. Alternating current that changes less than 1000 times per second is called low-frequency current, and that greater than 1000 times is called high-frequency current, and radio frequency is such a high-frequency current. Cable television system is the use of radio frequency transmission
In the theory of electronics, when the current flows through the conductor, the magnetic field will be formed around the conductor; when the alternating current passes through the conductor, the alternating electromagnetic field will be formed around the conductor, which is called electromagnetic wave.
When the frequency of electromagnetic wave is lower than 100kHz, the electromagnetic wave will be absorbed by the earth's surface, and can not form effective transmission. However, when the frequency of electromagnetic wave is higher than 100kHz, electromagnetic wave can spread in the air and reflect through the ionosphere at the outer edge of the atmosphere to form a long-distance transmission ability. We call the high-frequency electromagnetic wave with long-distance transmission capability as radio frequency
Composition and characteristics of RF circuit
The RF circuit of ordinary mobile phone is composed of receiving channel, transmitting channel and lo circuit. It is mainly responsible for receiving signal demodulation and transmitting information modulation. The early mobile phones demodulate the received baseband information only after the superheterodyne frequency conversion (mobile phones have, two-stage mixing and one and two local oscillator circuits); the new mobile phones directly demodulate the received baseband information (zero if). In some mobile phones, the frequency synthesizer and receiver voltage controlled oscillator (rx-vco) are also integrated in the intermediate frequency.
What is the difference between high frequency PCB and RF PCB
High power, through the antenna or RF transmitter to the outside world or radiate high-frequency electromagnetic wave circuit is called radio frequency circuit. The characteristic of RF circuit is that it can emit high frequency electromagnetic wave to the outside world.
High frequency circuit generally refers to the circuit that can run, receive, generate, amplify, conduct, or process high-frequency signals. RF circuit is also a kind of high frequency circuit.
