< Previous - Table of Contents - Next > TRIODE DEGENERATIVE AMPLIFIERS
The equation for the gain of this amplifier was derived in Chapter 2, and is:
K = ( -gm* RL ) / [ 1 + ( gm+ gp ) Rk1 + ( gp* RL ) ] (8)
where Rk, is the portion of the cathode bias resistor which is not by-
passed. The equation for the load line for this amplifier is slightly
modified from that of the ordinary triode amplifier:eb = Ebb - ib ( Rk1 + RL ) (23)
In other respects, the design technique is unchanged.
Example 13. To illustrate the effect of degeneration clearly, the de-
sign of Example 4, Case 1, may be modified by assuming Rk1 = 400 ohms.
Find the change of amplification and distortion.As Rk1, is negligible compared to RL, the same data may be used, giving:
.
ec 0 -2 -4 -6 -8 volts
K -14.1 -13.0 -11.8 -10.7 -9.4
.
DISTORTION
The distortion generated by the degenerative amplifier may be calcu-
lated using either Equation 15 or the Fourier technique. Using Equa-
tion 15 with a peak-to-peak signal voltage es of 8 volts, the amplifier
of Example 13 will have a distortion of 5%. In a similar manner, a
peak signal of 4 volts yields a distortion of 2.4% ( Ec1 = -4 volts ). As
can be seen from page 13, the distortions without degeneration are 6.0
and 3.0%, respectively.
THE PENTODE DEGENERATIVE AMPLIFIER
The amplification equation for the pentode degenerative amplifier has
been derived on page 8; it is:K = ( -Gm1* Xp* RL ) / [ 1 + ( Gm1* Xp* Rk1 )] (10)
The plate-to-cathode voltage, and the voltage to ground, are given by
the equations:eb = Ebb - { Ip [ Xp ( Rk1+ RL ) + ( Xc2* Rk1 ) ] }
EK = Ip ( Xp + Xc22 ) Rk
ek = Ip* Xp* Rk1
The second of this group is used to calculate the bias, and the third
the degenerative signal voltage.
20
< Previous - Table of Contents - Next >
Copyright 2008 for Phyllis K. Pullen, M.D.,
by Robert J. Legg