Figure 2-6.Series peaking coil.
You know that the capacitive reactance of COUT and CIN will limit the high-frequency response of the
circuit. L1 is the series peaking coil. It is in series with the output-signal path and isolates COUT from CIN.
R4 is called a "swamping" resistor and is used to keep L1 from overcompensating at a narrow range of
frequencies. In other words, R4 is used to keep the frequency-response curve flat. If R4 were not used
with L1, there could be a "peak" in the frequency-response curve. (Remember, L1 is called a peaking
If a coil is placed in parallel (shunt) with the output signal path, the technique is called SHUNT
PEAKING. Figure 2-7 shows a circuit with a shunt peaking coil. With the exceptions of the "phantom"
capacitor and the inductor, the components in this circuit are the same as those in figure 2-6. R1 is the
input-signal-developing resistor. R2 is used for bias and temperature stability. C1 is the bypass capacitor
for R2. R3 is the load resistor for Q1 and develops the output signal. C2 is the coupling capacitor which
couples the output signal to the next stage.