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SECTION
1 1 1
THEORY O F OPERATION
3-1
DISTRIBUTED
AMPLIFIER
The extremely rapid r i s e time of the
460B
i s obtained through the
use of the distributed amplifier;* the operation of which i s explained
as followsa
See Figure 5.
In the distributed amplifier, the tubes a r e connected at fixed i n t e r -
vals between two artificial transmission lines that have equal p r o -
pagation velocities.
A signal applied to the input terminals passes
down the grid line and appears on each grid in turn.
The resulting
plate signal currents flow in the plate line, half in one direction
and half in the other.
tube to the output a r e the s a m e length in t e r m s of line sections
traversed, the individual plate signal c u r r e n t s will a r r i v e at the
output termination in phase, thus adding together in the load.
The
plate signal currents flowing in the r e v e r s e direction a r e absorbed
without reflection in the r e v e r s e plate line termination.
put voltage of a distributed amplifier is given by the relation
Eo
-
plate signal current, and Zp i s the plate line impedance.
Since the paths f r o m the input through any
The
out-
-
nZp
- r i p where n is the number of tubes in the stage, i p is the
The number of tubes that can be used in a single stage i s limited
by g r i d loading which occurs at high frequencies because of the
increased input conductance of the amplifier tubes.
This effect
reduces the high frequency gain and in effect r e s t r i c t s the f r e -
quency range of the amplifier.
When amplifiers a r e cascaded, the r i s e time will be g r e a t e r than
that of a single unit in accordance with the relation:
T =
112
where:
T is total r i s e time
t is the r i s e time of a single
n is the number of
460
units.
unit (2mbXlO-9 sec.)
In
addition to the r i s e time of the amplifiers, the r i s e time of the
RC
combination formed by the capacitance of the deflection g a t e s
*
Ginzton, Hewlett, e t all, Distributed Amplification, Proc.
IRE,
Vola
3 6 ,
August,
1948
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