Sect. III Page 3
reference. When V3B conducts the Bi-Stable Unit is virtually no signal at the junction of R and C the
is flipped back to its original state, completing one output voltage must also be triangular.
cycle of operation.
In this case the frequency of the applied signal is so
Voltage regulator tubes V5 and V6 are connected low that the amplifier used must be direct coupled.
by a voltage divider from which the switching refer- There is a net voltage rise between input level and
ence voltages are taken. They also provide the output level in a dc amplifier. In this particular
limiting voltages applied tubes to V7 and V8 which application the average output level is determined
are seen to be a push-pull clamping system. In- as the average of the "plus reference" and "minus
asmuch as the integrator output is directly related reference" levels, the since output excursion is
to the input, it is seen that the magnitude of square- limited to these levels. B this level does not coincide
wave applied must be carefully controlled. Al- with the average level of the applied squarewave,
though only the squarewave appearing at the plate then the positive negative and excursions of the
of Vl is needed to drive the integrator, the clamp squarewave will not be equal, resulting in unequal
is made push-pull to prevent excessive current rise and fall rates of the output triangle. Because
variations in the regulator tubes. The action of the squarewave input is generated from the triangular
V7B and V8B is such that if the applied waveform output by the bi-stable circuit, the net result is that
has peak excursions in excess of the potentials on under such conditions the squarewave is really a
the remaining cathode and plate, these being deter- rectangular wave. The resulting rectangular wave
mined by regulator tubes V5 and V6, a current will has an average value just equal to that demanded
flow through R20 which drops the voltage to very of the amplifier input by virtue of the pre-set output
nearly the potential of the regulated element of the level. The average levels of the input and output
conducting section of the diode. The action of the are stabilized by the use of a differential amplifier
other diodes is the same, but 180" out of phase, that has high gain to the difference between the volt-
inasmuch as they are coupled to the plate of V2. age applied its to inputs but little or no gain to any
In this way, waveforms appearing on the clamped voltage change common to both inputs.
sides of R21 and R20 are assured to be of equal
magnitude as well as 180" out of phase, and further Figure 3-4 shows how this is done. The right hand
the average of dc level of the squarewave is ac- grid of the differential amplifier V15, is the signal
curately controlled. input and is driven through R by the rectangular
wave appearing on the FREQUENCY control. The
average voltage of this rectangular wave is depen-
3-3 LINEAR INTEGRATOR dent on the clamping levels and the ratio of "on" to
"off" time. When the system is adjusted for equal
Consider the block diagram of the linear of feed- on-off times (squarewave) the average is just the
back integrator shown as in Figure 3-3. Starting average of the clamping levels. The left hand grid
with the output voltage E,, it is seen that if the gain has no signal because the voltage divider which in-
of the amplifier is high, then the signal appearing cludes the balance control is connected the to no-
at the junction of R and C (the amplifier input) must signal sides of the clamping tubes. However, any
be small. For a fixed output Eo as the gain is in- change in the clamping level changes the average
creased the resultant signal at the input of the am- level appearing on both input grids in the same
plifier becomes arbitrarily small. Since the voltage amount. Due to the large common cathode resistors
at the junction at R and C is arbitrarily small, a of V15 and V16 a common mode change has very
squarewave applied to input the will cause a constant little effect. The input to the left hand grid has
current in R. Because the current charging and dis- another function. If the balance control R60, is
charging C is constant, except for direction, the varied slightly, the output of the amplifier will show
voltage across C will be triangular. Since there a considerable change in average level; and therefore
- - -
- AMP -
?9, Eour
ID-"-5.
t a
Figure 3-3. Generalized Miller or Feedback Integrator |
ACEC
