Yuan what does parts of an apparatus have to differ in low frequency and high frequency character?
[introduction] we first for say capacitance, say character of low frequency of large electric capacity is good, small electric capacity is high frequency and characteristic good, so become the word for inverse ratio according to the size of capacitive reactance and capacitance C and frequency F, it is large electric capacity not only low frequency character is good, high frequency character is better, because frequency is taller, the size is larger, capacitive reactance is lower, high frequency whether to pass large electric capacity more easily, but the rate that charges discharge from large electric capacity is slow the word for, high frequency seem to be passed not easily again, is this very not contradictory?
Above all, high frequency low frequency is opposite. If frequency is too tall, so, the capacity of capacitance becomes again big also no point, because, everybody knows, coil is inductance, it is block is high frequency, frequency is taller, block up effect is bigger. Although inductance amount is very small, but, high capacity capacitance has commonly bring foot and bigger plate group longerly to be together, at this moment, the equivalent inductance amount of capacitance bipod is already right high frequency had very big block up effect.
Accordingly, high frequency the high capacity that needs not easily through high frequency function electroanalysises capacitance, the capacitance of pottery and porcelain of a shape takes an advantage on price performance.
Manage together, pairs is inductance bigger high frequency is block up effect bigger? Either. To get bigger inductance is measured, must have as far as possible much, as far as possible big coil, and these conductor with respect to countless plate to capacitance, if chance these plate span closer word (this is pursuit many number cannot avoid) , distributinging capacitance can provide access to high frequency signal.
So, different frequency paragraph the capacitance that signal wants to choose proper size and inductance.
Below we together 3 the most commonly used passive parts of an apparatus, the high frequency and equivalent circuit of resistor, capacitance, inductance analyses:
1. high frequency resistor
Circuit element of the prevailing in low frequency electronics is resistor, its action is the purpose that will achieve voltage to reduce through spending outfit of a few electric energy heat energy. The high frequency and equivalent circuit of resistor is shown like plan institute, among them resistor of imitate of two inductance L the parasitism inductance of the down-lead of two end, the structure that still needs fibrous root seizes actual lead at the same time considers capacitance effect; With effect of depart of charge of capacitance C imitate.
Notation of resistor equivalent circuit
According to the equivalent circuit graph of resistor, OK and convenient computation gives the impedance of whole resistor:
Next graphs described the relationship of the impedance absolute value of resistor and frequency, positive-appearing image sees in that way, the impedance of the resistor when low frequency is R, when lift when frequency however and be worth certainly more than, the influence of parasitism capacitance is become main, it causes the fall of resistor impedance. When frequency continues to lift, as a result of the influence of down-lead inductance, total impedance rises, down-lead inductance represents line of an open a way or infinity impedance below very tall frequency.
A typical 1K? The relation of resistor impedance absolute value and frequency
2. high frequency capacitance
Piece the shape capacitance application in radio frequency circuit is very wide, it can be used at filter frequency modulation, match network, transistor slant in a lot of circuit such as buy, accordingly very the high frequency character that is necessary to understand them. The high frequency and equivalent circuit of capacitance is shown like plan institute, among them the parasitism inductance that L is down-lead; Loss of descriptive down-lead conductor uses the equivalent resistor R1 of a series connection; Descriptive dielectric loss uses a shunt-wound resistor R2.
Notation of capacitance equivalent circuit
Can get the impact of the impedance absolute value of a typical capacitor and frequency likewise. Following plan institute are shown, because be put in dielectric loss to mix finite long lead, capacitance shows as same as resistor syntonic character.
The relation of an absolute value of typical 1pF capacitance impedance and frequency
3. high frequency inductance
The applied photograph of inductance is less to resistor and capacitance, it basically uses what Yu Jing body is in charge of to slant in buy network or filter. Inductance is circled on round conductor column by lead normally make and become, because of this inductance the perceptual feature besides consideration itself, still need to consider the distributinging capacitance between the resistor of lead and photograph adjacent coil. Following plan institute show the equivalent circuit model of inductance, the integrated effect that C of parasitism bypass capacitance and R of series connection resistor bring by distributinging capacitance and resistor respectively.
The equivalent circuit of high frequency inductance
As identical as resistor and capacitance, the high frequency character of inductance is same the anticipation with ideal inductance is characteristic and different, following plan institute show: Above all, when frequency approachs syntonic point, the impedance of high frequency inductance rises quickly; The 2nd, when frequency continues to rise, the influence of parasitism capacitance C is become main, coil impedance is reduced gradually.
The relation of inductance impedance absolute value and frequency
Anyhow, in high frequency circuit, the resistor with lead basic along with, capacitance and inductance the function of these basic passive parts of an apparatus is apparent differ with ideal component feature. The reader can discover the constant resistance when low frequency, to high frequency when show have syntonic place 2 rank the system is corresponding; Be in high frequency when, the dielectric in capacitance produced loss, the ability when causing the impedance feature that appears since capacitance to have low frequency only and frequency become inverse ratio; When low frequency the impedance of inductance answers along with the addition of frequency line form to increase, deviate ideal feature begins before reaching syntonic point, turn into finally capacitance sex. These passive component can be passed in high frequency character in front mentioned quality factor description, to capacitance and inductance, for harmonious purpose, hope normally arrive as far as possible high quality factor.