One, high frequency circuit introduces

 

Spoken parts in an opera of high frequency circuit is radio circuit, but do not involve microwave circuit (microwave is used at handling circuit of one hertz above, want the electromagnetism field proceed with from physics, with us common circuit is very different) , use at radio wave to blast off, receive, modulation, demodulation, enlarge is waited a moment.

 

Digital circuit processes digital signal, digital signal has on any account only two kinds of signal (for instance, the bend over of 0-3.3 of limits of digital circuit work of CMOS craft, 0-0.8 bend over considers as low n, 2.4-3.3 bend over considers as tall n, other voltage considers as invalid, the alignment) that distributes all report signal into n of on any account to comprise, comfortable at high speed processing, high accuracy is handled, with computer interface, use the computer to handle directly.

 

Imitate circuit does not distinguish n, all and successive signal is handled together (the macroscopical physical quantity of nature is successive) , use at wave of power source, enlarge, filter to wait a moment.

 

Imitate circuit and high frequency circuit are close to actually very much, just circuit job frequency is tall, the physical character that makes yuan of many parts of an apparatus or appliance produces a change, processing technique and the issue that handle differred.

 

Index of function of high frequency circuit

 

Enlarge of high frequency small signal has syntonic enlarge and broadband enlarge form of two kinds of circuit, function index basically includes a few as follows.

 

1, gain

 

High frequency circuit and low frequency circuit are same, have the index of voltage gain and power gain. To syntonic enlarge circuit, it is to show in syntonic frequency F0 is in, to broadband enlarge circuit, it is to show in a paragraph of frequency bubble is surrounded.

 

2, transmission bands

 

With likeness of concept of low frequency circuit, to syntonic enlarge circuit, transmission bands is to show relative to Yu Xie Zhen Pin leads F0, normalization drop unexpectedly the poor; of two corresponding frequency of 0.707 magnifies to the broadband circuit, it is the corresponding definition that leads at a paragraph of frequency relatively.

 

3, alternative

 

Basically be aimed at syntonic enlarge circuit optionally, token circuit chooses useful signal to control the capacity of useless signal, mix with square ratio normally restrain than measure, it is the syntonic and characteristic curve that is based on circuit.

 

4, noise coefficient

 

When enlarge circuit works, because meeting generation holds a variety of accounts,flow child irregular motion, noise is formed in circuit interior, make signal quality is affected. This kind of influence uses signal power Ps and noise power Pn normally than (abbreviation letter a confusion of voices is compared) will describe. Noise coefficient definition believes what comparing of a confusion of voices and output letter a confusion of voices compare to compare for the input.

 

5, stability

 

The stability of circuit of high frequency enlarge is when showing working status or condition produce change, its are main the stable rate of function. For example, the wave motion of the change of environmental temperature or power source voltage, the parameter of circuit element of; of dc job status that can affect enlarge circuit also can be changed, bring about enlarge circuit gain to produce change, central frequency deflection, syntonic curve distortion. Produce self-excitation even and cannot work completely.

 

Principle of ground connection of high frequency circuit

 

Taller to working frequency circuit and digital circuit, because the down-lead of each yuan of parts of an apparatus is mixed,the inductance of the layout itself of circuit will increase the impedance of ground wire, the method of a bit ground contact that uses extensively in low frequency circuit consequently. If be used in high frequency circuit to increase the impedance of ground wire easily, and the stray inductance that ground wire asks also can cause the mutual coupling between circuit with distributinging capacitance, make circuit works to be not stabilized thereby.

 

The stray inductance that reduces ground space to reduce ground wire impedance to reach its causes the mutual coupling between circuit with distributinging capacitance. High frequency circuit uses nearby ground contact, namely the principle of many bits of ground connection, receive the nearby of systematic ground wire of each circuit to low impedance ground wire to go up, generally speaking, when the 10MHz of working frequency prep above of circuit, should use the means of many bits of ground connection. Because the ground connection key of high frequency circuit is the stray that reduces ground wire as far as possible,inductance is mixed distributinging capacitance, there is very big distinction with low frequency circuit on the executive method of ground connection so.

 

 2, radio frequency circuit introduces

 

RF of radio frequency abbreviation, radio frequency is radio frequency electric current, it is the abbreviation of electromagnetic wave of change of a kind of high frequency communication. The alternating current that every second change is less than 1000 times calls low frequency electric current, be more than 1000 times call high frequency electric current, and radio frequency is a kind of such high frequency electric current. Cable television system uses radio frequency to transmit means namely

 

In electronics theory, electric current has shed conductor, magnetic field; can be formed to hand in all round conductor change electric current passes conductor, meeting form clinchs a deal all round conductor the electric magnetic field that change, call electromagnetic wave.

 

In electromagnetic wave frequency under 100khz when, electromagnetic wave can be absorbed by the earth’s surface, cannot form effective transmission, but when 100khz of prep above of electromagnetic wave frequency, electromagnetic wave can travel in air, reflex via the ionosphere of the predestined relationship outside aerosphere, form remote transmission ability, we have remote the high frequency electromagnetic wave of transmission ability calls radio frequency, english abbreviate: RF

 

Composition of radio frequency circuit and characteristic

 

Circuit of radio frequency of common mobile phone by receive access, emissive access, this brace up 3 big circuit comprise circuit. Its basically are in charge of receiving signal demodulation; to launch information modulation. Inchoate mobile phone passes superheterodyne frequency conversion (the mobile phone has one class, 2 class mixing mixes, 2 brace up circuit) , ability solution v receives; of base band information after new-style mobile phone solves v to receive base band information directly () of 0 intermediate frequency. More some of mobile phone adds up to frequency, receive pressure accuse an oscillator (RX—VCO) is compositive also in intermediate frequency interior.

 

 

Power is greater, can launch the circuit that the head blasts off to the outside or radiation gives high frequency electromagnetic wave to call radio frequency circuit through aerial or radio frequency. The characteristic of report of radio frequency circuit can emit high frequency electromagnetic wave to the outside namely.

 

High frequency circuit is generally refer to can run high frequency signal, receive high frequency signal, or generate high frequency signal, or enlarge is high frequency signal, conduct high frequency signal, or the circuit that processes high frequency signal. Radio frequency circuit also is a kind of high frequency circuit.