Series Peaking

Solid State Devices and Solid State Power Supplies and Amplifiers
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____________________________________________________ Video and Radio Frequency Amplifiers

use of peaking coils will increase the frequency response of an amplifier circuit. However,

it will also lower the gain of the amplifier.

Series Peaking

6-30. The use of a peaking coil in series with the output signal path is known as SERIES

PEAKING. Figure 6-5 shows a transistor amplifier circuit with a series peaking coil. In the

figure, R1 is the input-signal-developing resistor. R2 is used for bias and temperature

stability of Q1. C1 is the bypass capacitor for R2. R3 is the load resistor for Q1 and

develops the output signal. C2 is the coupling capacitor that couples the output signal to

the next stage. "Phantom" capacitor COUT represents the output capacitance of the circuit,

and "phantom" capacitor CIN represents the input capacitance of the next stage. 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.

Figure 6-5. Series Peaking Coil

Shunt Peaking

6-31. If a coil is placed in parallel (shunt) with the output signal path, the technique is

called SHUNT PEAKING. Figure 6-6 shows a circuit with a shunt peaking coil. 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 that couples the output signal to the next stage.

6-32. The "phantom" capacitor, CT, represents the total capacitance of the circuit. Notice

that it tends to couple the output signal to ground. L1 is the shunt peaking coil. While it is

in series with the load resistor (R3), it is in parallel (shunt) with the output-signal path.

6-33. Since inductive reactance increases as frequency increases, the reactance of L1

develops more output signal as the frequency increases. At the same time, the capacitive

23 June 2005

TC 9-62

6-9

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