What is the phase shift in the analog circuit?
For low frequencies, the output phase is unaffected by the capacitance. When the cutoff frequency (f c) of the RC filter is reached, the phase drops to -45°. For frequencies above the cutoff frequency, the phase is close to the asymptotic value of -90°. This response simulates the phase shift caused by each shunt capacitor. The shunt capacitor will cause a phase shift between 0° and -90° on the resistive load. Of course, also pay attention to attenuation. A similar appearance to a series capacitor (eg, an AC coupling capacitor) shows the typical effect of this configuration.
In this case, the phase shift starts at + 90° and the filter is a high pass filter. Above the cutoff frequency, we finally stabilized to 0°. Therefore, we see that the series capacitor always has an effect between the +90° and 0° phase shifts. With this information, we can apply the RC model to any circuit we want. For example, such a common-shot amplifier. The amplifier's response is flat to around 10 MHz.
Only after about 10 MHz can we see a phase shift of less than 180° because the common emitter configuration is an inverting amplifier. Ignoring the early effects, the output impedance of the amplifier is R2 = 3kΩ, which is quite high. Place a shunt capacitor at the output. What happens at this stage?
Based on experience, a cutoff frequency of 53 Hz is expected, below which there should be a phase shift of 180° (capacitance has no effect), above which there will be a 180° - 90° = 90° phase shift (and many losses). . Note that this corresponds to a phase of -180° to -270°. Beginning to see the drive capacitive load can cause unexpected phase changes, which can cause severe damage to the undetected feedback amplifier. More commonly, a series coupling capacitor is found at the output.
I changed the circuit value and added a 100kΩ resistor load. Now we have a high-pass filter consisting of C1 and R3 with a cutoff frequency of only 1.6 Hz. We expect
The phase shift is the effect of the circuit causing voltage or current lead or lag from the input to the output. In particular, we will focus on how reactive loads and networks affect the phase shift of the circuit. Whether using oscillators, amplifiers, feedback loops, filters, etc., phase shifts have a variety of consequences. The detection circuit may change the effect further. Maybe you have a cavity that is used in the feedback loop of an oscillator, but this cavity only provides a phase shift of 90°, and you need 180°. How to replace?
The frequency phase shift is derived from reactive components: capacitors and inductors. This is a relative amount, so it must be given as the phase difference between the two points. As used herein, "phase shift" refers to the phase difference between the output and the input. It is said that the voltage of the capacitor lags behind the current by 90 degrees, and the current of the inductor lags behind the voltage by 90 degrees. In the phasor form, this is represented by + j or -j in the inductance and capacitance reactance, respectively. But to some extent, there are capacitances and inductances in all conductors. So why don't they cause a 90° phase shift?
All phase shift effects will be modeled by RC and RL circuits. All circuits can be modeled as sources with some source impedance, powering the circuit, and load following the circuit. The source impedance of the source is also referred to as its output impedance. All circuits can be modeled as a primary output with some output impedance, fed to the current stage, and loaded with the following stages of input impedance.
This will simulate some source circuits (such as amplifiers) with an output impedance of 50Ω, with a load of 10kΩ and shunted by a 10 nF capacitor. It should be clear here that the circuit is basically an RC low pass filter made of R1 and C1. It is known from basic circuit analysis that the voltage phase shift in the RC circuit will vary from 0° to -90°, as demonstrated by the simulation.
For low frequencies, the output phase is unaffected by the capacitance. When the cutoff frequency (f c) of the RC filter is reached, the phase drops to -45°. For frequencies above the cutoff frequency, the phase is close to the asymptotic value of -90°. This response simulates the phase shift caused by each shunt capacitor. The shunt capacitor will cause a phase shift between 0° and -90° on the resistive load. Of course, also pay attention to attenuation. A similar appearance to a series capacitor (eg, an AC coupling capacitor) shows the typical effect of this configuration.
In this case, the phase shift starts at + 90° and the filter is a high pass filter. Above the cutoff frequency, we finally stabilized to 0°. Therefore, we see that the series capacitor always has an effect between the +90° and 0° phase shifts. With this information, we can apply the RC model to any circuit we want. For example, such a common-shot amplifier. The amplifier's response is flat to around 10 MHz.
Only after about 10 MHz can we see a phase shift of less than 180° because the common emitter configuration is an inverting amplifier. Ignoring the early effects, the output impedance of the amplifier is R2 = 3kΩ, which is quite high. Place a shunt capacitor at the output. What happens at this stage?
Based on experience, a cutoff frequency of 53 Hz is expected, below which there should be a phase shift of 180° (capacitance has no effect), above which there will be a 180° - 90° = 90° phase shift (and many losses). . Note that this corresponds to a phase of -180° to -270°. Beginning to see the drive capacitive load can cause unexpected phase changes, which can cause severe damage to the undetected feedback amplifier. More commonly, a series coupling capacitor is found at the output.
I changed the circuit value and added a 100kΩ resistor load. Now we have a high-pass filter consisting of C1 and R3 with a cutoff frequency of only 1.6 Hz. We expect