Phase is the position of a wave in its cycle at a specific time:peak、troughOr the scale of a point between them[1]。Phase describes the change of signal waveformmeasure, usually in degrees (angles), also known asphase angle。 When the signal waveform changes in a periodic manner, the waveform cycle is 360 °.
stayfunctionY=Acos (ω x+φ), ω x+φ is called phase.
In AC, the phase reflects the state of AC at any timephysical quantity。The magnitude and direction of alternating current varies with time.such asSinusoidal AC current, whose formula isi=Isintwoπft。iIs the instantaneous value of AC current,IIs the maximum value of AC current,fIs the frequency of alternating current,tIs the time.As time goes by, AC current can change from zero to maximum, from maximum to zero, from zero to negative maximum, and from negative maximum to zero.staytrigonometric functionintwoπftIt is equivalent to radian, which reflects the state of AC at any time, whether it is increasing or decreasing, positive or negative, and so on.So puttwoπftIt's called phase, or phase[2]。
phase noise
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phase noise It is another kind of signal timing changemeasureThe result ofFrequency domainInternal display, yesfrequencyDomainconcept。Phase noise refers to the ratio of the noise density per Hz to the total signal power, which is represented by the random drift of the carrier phase. It is an important index to evaluate the spectral purity of the frequency source (oscillator).Phase noise actually describes the short-term stability of the carrier frequency (phase), which is due to the random fluctuation of the output signal phase caused by various noises in the system.In the frequency domain, the phase noise is the sideband noise around the carrier spectrum, which reflects the short-term instability of the signal waveform.The smaller the phase noise, the higher the spectral purity of the signal and the better the frequency stability.
The calculation formula of phase noise is: PN (f)=PN0+10log (f/f0)+10log (Δ f/BW).
In this formula, PN (f) represents the phase noise, PN0 is the out of band signal strength, f is the signal frequency, f0 is the out of band signal frequency level, Δ f is the noise bandwidth, and BW is the original signal bandwidth.This formula can be used to estimate the phase noise level under different frequency and bandwidth conditions.
withoutphase noise , then the whole power of the oscillator should be concentrated at the frequency f=f0.However, the appearance of phase noise extends part of the oscillator power to adjacent frequencies, resulting in sidebands.
phase noise Usually defined as d at a given offset frequencyBC/Hz value, where dBc is the ratio of power at this frequency and total power in dB.An oscillator at a certain offset frequencyphase noise It is defined as the ratio of signal power within 1Hz bandwidth at this frequency to the total power of the signal.
phase difference
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Two with the same frequencyalternating currentThe difference of phase is called phase difference, or phase difference.These two alternating currents with the same frequency can be two alternating currentselectric current, can be two exchangesVoltage, can be two exchangesemf, or any two of the three quantities[3]。
For example, the phase difference between the AC voltage applied to the circuit and the AC current passing through the circuit is studied.If the circuit is pureresistance, then the phase difference between the AC voltage and the AC current is equal to zero.That is to say, when the AC voltage is equal to zero, the AC current is also equal to zero. When the AC voltage reaches the maximum value, the AC current also reaches the maximum value.This condition is called in-phase, or in-phase.If the circuit containsinductanceandcapacitanceThe phase difference between the AC voltage and the AC current is generally not equal to zero, that is, it is generally different from the phase, or the voltage is ahead of the current, or the current is ahead of the voltage.
Add totransistoramplifierBaseAC voltage on and fromcollectorThe phase difference between the output AC voltage and the output AC voltage is exactly 180 °.This situation is calledAntiphaseBit, or inverted phase.
Simple harmonic motionPhase difference in: if the frequencies of two simple harmonic motions are equal, their initial phases areφ1，φ2。Whenφ2>φ1Their phase difference is
△φ=(ωt+φ2)-(ωt+φ1)=φ2-φ1
At this time, we often say that the phase of 2 is ahead of that of 1△φ。
