2-5On figure 2-1, the two points marked f1and f_{2} will enable you to determine the frequency-responselimits of the amplifier. In this case, the limits are 15 hertz (15 Hz) and 20 kilohertz (20 kHz). You shouldnow see how a frequency-response curve can enable you to determine the frequency limits and thebandwidth of an amplifier.READING AMPLIFIER FREQUENCY-RESPONSE CURVESFigure 2-2 shows the frequency-response curves for four different amplifiers. View (A) is the samefrequency-response curve as shown in figure 2-1. View (B) is the frequency-response curve of anamplifier that would also be classified as an audio amplifier, even though the curve is not "flat" from 15hertz to 20 kilohertz and does not drop off sharply at the frequency limits. From the curve, you can seethat the lower frequency limit of this amplifier (f_{1}) is 100 hertz. The upper frequency limit (f_{2}) is 10kilohertz. Therefore, the bandwidth of this amplifier must be 10 kilohertz minus 100 hertz or 9900 hertz.Most amplifiers will have a frequency-response curve shaped like view (B) if nothing is done to modifythe frequency-response characteristics of the circuit. (The factors that affect frequency response and themethods to modify the frequency response of an amplifier are covered a little later in this chapter.)Figure 2-2A.—Frequency response curves.