Representation method of frequency response → Ges to the frequency characteristics of the co-reconstant circuit → Qualitative analysis of its characteristics and formation, while introducing several concepts (f L, F h, bw) → frequency distortion.
3.1.1 Representation of frequency response
A ˙ u (f) = a u (f) ∠φ (f)
A u (f) - amplitude frequency characteristics
φ (f) - phase frequency characteristics
The amplitude and phase frequency characteristics of a typical single tube co-amplifying circuit are shown in Figure 3.1.
It can be seen from the amplitude frequency characteristics: low frequency band, with the decrease in frequency f, a magnification decreased; high frequency segment, with the increase of frequency f, the magnification decreases.
Causes:
Low frequency segment, with the decrease in frequency f, the capacitive increase of the coupling capacitance increase → the voltage reduction of the amplifying circuit input is reduced by the voltage reduction of the amplifying circuit input → the output voltage drop → the magnification decreases.
High frequency segment, with the increase of frequency f, the capacitive capacitance of the triode is reduced → its divergence enhancement → actually amplified current reduction → magnification decreases.
From the phase frequency characteristics, it is possible to generate 0 ° to 90 ° super-additional phase shift Δφ than the medium frequency segment, and the high frequency band generates 0 ° to -90 ° lag additional phase shift Δφ.
3.1.2 lower limit frequency, upper frequency and passband
F L - lower limit frequency
f h - upper limit frequency
BW - pass frequency band, where bw = f h - f L
Tong frequency band characterizes the response capability of amplifying circuits on different frequency input signals, the stronger the response ability of different frequency input signals. It is one of the important technical indicators of amplifying circuits.
3.1.3 frequency distortion
Due to the limit of the passband BW, the amplification circuit is different from the magnification and phase shift of different frequencies, so when the input signal contains multiple harmonics, the output waveform generates distortion, referred to as frequency distortion. Frequency distortion includes amplitude distortion, phase frequency distortion.
Amplitude distortion: the distortion caused by the magnification of the magnification of different frequencies in different frequencies.
Phase frequency distortion: A distortion caused by the phase shift of the enlarged circuit of different frequencies.
For example, it is assumed that the input signal contains two sine quantities in the input signal, as shown in FIG. 3.2 (a), if the amplified circuit is equally amplified by the signals of the two frequencies, and the resulting phase shift is also the same, Then it is not distortion output waveform shown in Fig. 3.2 (a); if the magnification of the signal to the frequency of F 2 is reduced, as shown in Fig. 3.2 (b), the distortion waveform shown in Fig. 3.2 (b) is obtained. This distortion is amplitude distortion; if the amplified circuit is different from the signal of F 1 and F 2, as shown in Fig. 3.2 (c), the distortion waveform shown in Fig. 3.2 (c) is obtained. This distortion is a phase frequency distortion. , Read the full article, original title: General concept of frequency response
Article Source: [Micro Signal: EET-China, WeChat public number: Electronic Engineering Album] Welcome to add attention! Please indicate the source of the article.
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