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Патент USA US3070766

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Dec. 25, 1962
M. FISCHMAN
3,070,756
AMPLITUDE STABILIZED SAWTOOTH CURRENT GENERATOR
Filed May 7, 1959
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Patented Dec. 25, 1962
2
3,070,756
The condenser 30 is connected as shown between the
base 8 and the conductor 18 which may be maintained at
Martin Fischman, Wantagh, N.Y., assignor to Sylvania
a low A.C. potential or grounded by the action of large
bypassing condenser 19, insofar as the generated oscilla
tions are concerned. Resistor 32 in series with the yoke 2
is a monitoring resistance from which a sampling voltage
may be derived by way of lead 34 for test and adjustment
AMPLETUDE gTABILHZED SAWTOOTH (INT
GENERATQR
Electric Products line, a corporation of Delaware
Filed May 7, 1959, Ser. No. 811,649
5 Qlaims. (Ci. 331-109)
purposes.
My present invention relates to a generator of electrical
Transistor T2 serves to maintain the average current
10 through the entire circuit constant. Transistor T2 is
currents of sawtooth waveform.
In the generation of linear sawtooth currents in de?ec
provided with an emitter electrode 40, a base electrode 42,
tion coils that are primarily inductive, a problem arises in
and a collector 44. Emitter 40 is connected to ground
connection with maintaining the sawtooth amplitude in
through a resistor R3 thus providing degeneration in the
dependent of the sawtooth frequency. For example, when
emitter circuit. The voltage applied to the base 42 with
laboratory Oscilloscopes are supplied with de?ecting cur
rents from conventional sawtooth generators, undesirable
respect to emitter 40 of transistor T2, is controlled by a
changes in de?ection of the oscilloscope beam take place
at different frequencies, requiring time consuming re
Resistor R2 as shown, is in series with resistors R5 and
R4, the series combination of resistors R2, R5 and R4,
being connected between the negative terminal 22 of
power supply 24 and ground.
adjustment or use of different scales and calibrations.‘
It is, therefore, an object of my present invention to
provide a sawtooth current generator in which the peak
to peak values of the sawtooth current waveforms gen
erated are maintained constant over a range of operating
l.
u".1
tap 46, adjustably connected along and to resistor R2.
If desired, modulating voltages such as voltages from
a commercial 60 cycle source 53 may be introduced be
tween the base 42 and emitter 40 by means of a trans
frequencies. Another object of my invention is to pro
former 50 connected as shown. The primary winding 51
vide a new, effective and relatively inexpensive amplitude 25 of transformer 50 is connected to the 60 cycle source 53
stabilized sawtooth current generator.
and the secondary winding 52 of transformer 50 is, as
Brie?y, my invention makes use of a transistorized
illustrated, connected in series with base 42 and the tap 46
sawtooth generator connected to an inductive load such
connected to resistor R2.
'
The operation of my improved sawtooth generator may
that currents of sawtooth form are caused to flow in the
inductive load. By means of a current regulating transis 30 be followed and understood more readily by considering
tor circuit, average current through the entire system is
the system ?rst, without reference to the amplitude stabil
ization feature. Referring to FIG. 1 (assuming point A
maintained constant. As a result, when changes in fre
to be grounded) it can be seen that transistor T1 provides
quency are made, automatic, compensating voltage varia
regenerative feedback from emitter 4 to base 8. The feed
tions take place across the inductive load in such a way
that the peak to peak ?ow therethrough is independent of
back is of a magnitude sufficient to cause the transistor
the frequency of operation.
to operate in the saturation region of its characteristic.
In this condition the transistor voltages remain practically
in an equilibrium state due to the lack of dynamic gain
FIG. 1 is a wiring diagram of an amplitude stabilized
of the transistor in the saturation region for an interval
40 corresponding to the forward scan of the cycle. FIG
sawtooth generator according to my present invention;
URES 2B, F, G, and H show this equilibrium state of the
FIG. 2 illustrates de?ection generator waveforms and
voltages on the transistor elements during this interval.
are used herein by way of explanation of the operation of
The duration of this interval depends on the time required
my present invention; and
My invention will be described in greater detail, herein
after, with the aid of the accompanying drawing wherein:
FIG. 3 is an illustration of characteristic curves of a
transistor showing the relationship of collector current to
collector voltage at different base currents.
In my invention, as illustrated in FIG. 1, currents of
sawtooth form are caused to ?ow in'the inductive load
here indicated as a coil 2, usually the de?ecting yoke for
a cathode ray tube. In accordance with my present inven
tion the peak to peak value of this current ?ow through
coil 2 is maintained constant over a desired operating
range of sawtooth wave frequencies.
The sawtooth currents through the'load 2 are generated
by the transistor generator comprising the transistor T1
having an emitter-electrode 4, a collector 6 and a base 8.
for the collector current, starting from zero current, to
reach the sharp knee in the collector characteristic for the
?xed base current that is applicable.
When the knee is reached the rate of change of col
lector current decreases and the ‘ transformer voltages
start to drop resulting in decreased base drive. This
50 process occurs quite rapidly, due to the 'fact that the op
erating point is now out of the saturation region and the
regenerative feedback of the circuit results in rapid cut
off of the transistor. The transformer voltage swings
through approximately a half cycle of oscillation deter
55
mined by the effective inductance and capacity of the cir
cuit and the transistor loading including the internal re
sistance and capacitance of the transistor, whereupon the
oscillation is arrested when the transistor turns-on and
Regeneration is provided by means of the autotransformer
AT having its upper or high potential terminal 10 connect
the next period of forward scan is initiated by the turn
ed to the base 8 by way of the variable resistor R1. An
60 on of the transistor.
intermediate point 12 of the autotransformer AT is con
During the forward scan interval both junctions of
nected by way of conductor 14 to the emitter of transistor
the transistor are forward biased. Low voltage drops
T1. The lower terminal 16 of autotransformer AT is con
therefore exist across the junctions of the transistor result
nected by way of conductor 18 and bypass condenser 20
to the collector 6 of transistor T1. A negative voltage 65 ing in an e?icient switch that connects the supply voltage
--V across the de?ection yoke 2 and the emitter tap 12 of
—V is applied to the collector 6, this voltage being derived
the transformer AT. The base current or drive is deter~
from the negative terminal 22 of a power supply 24, here
mined by the voltage between the emiter 4 and the
illustrated as a battery, grounded at its lower terminal 26.
stepped-up end 10 of the transformer AT and the value
“Shunting the terminals 22, 26 of battery 24 is a bypass
of R1, the frequency control resistance. This resistance
.condenser 25. The value of the voltage applied to col 70 is high in comparison-to the base to emitter resistance
lector 6 is adjusted to a suitable value by adjustment of
of the transistor T1, ‘under this operating condition. Dur
' the source voltage 24.
~-ing the forward ‘scan intervaL-the' base ‘current-is fairly
3,070,756
4
3
the yoke inductance and T is the duration of the sawtooth
constant ‘since the voltages referred to above, the emitter
voltage and the voltage at the high end 10 of the auto
transformer, are practically constant. The waveform of
or time of one cycle of the sawtooth waveform.
The average value of the sawtooth current drawn by
transistor T1 is approximately Ipp/ 2 if the ratio of trace to
retrace time is large as is usualy the case. In accordance
with my invention, I provide a transistor T2 to maintain
the base current of the transistor during the forward scan
interval is shown in FIG. 2-1. With the 1:3 autotrans
former used in the circuit of FIG. 1, a simple approxima
.tion for the base current useful for practical purposes is:
the average current through the circuit constant. By
maintaining the average current constant, the peak to
peak current will likewise remain constant and desired
10 stabilization ensues. Transistor T2 is connected with its
In the foregoing equation, E is the voltage across the
emitter grounded through a resistor R3; emitter degen
lower section 12-16 of transformer AT, and is substantial
eration being provided by resistor R3 and the low base
2E
Ib-fR1
ly equal, during saturation, to —-V.
resistance of transistor T2. The high dynamic collector
Estimated and measured values of base current at the
resistance thus obtained maintains the collector current
end of .the forward scan interval indicate a value of ap 15 practically independent of the collector voltage. Under
proximately 4 ma. Referring now to the collector char
these conditions the collector current of T2 will be ?xed
acteristics of FIG. 3, it can be seen that the transistor
by its base bias permitting the voltage drop across the
will be in the saturation region for collector currents up
scanner circuit to vary in accordance with Formula 1
to 200 ma. with a 4 ma. base drive provided that the
while maintaining the average current through the entire
collector to emitter voltage is small. The emitter voltage 20 circuit constant. Thus for a given DC. current deter
waveform of FIG. 26 shows a .collector to emitter drop
mined by the bias of transistor T2 adjustments of the fre
of about .4 volt near the end of the forward scan interval.
quency of the scanner will result in automatic compensat
FIG. 2E shows that the collector current increases to a
ing variations in the voltage E across yoke 2 with the re
maximum value of 200 ma. corresponding to the knee in
sult that Ipp remains independent of the frequency of the
the collector'characteristic for a base drive of 4 ma. 25 scanner. For example, at higher frequencies the volt
The locus of the operating point of the transistor then
age across the yoke 2 will rise, thereby maintaining the
falls out of the saturation region terminating the forward
peak to peak current through the yoke of unchanged
value. The peak to peak scanning current will be ‘in
The duration of the forward scan may be estimated
dependent of the characteristics of T1, the value of the
with reasonable accuracy provided some simplifying as 30 yoke inductance, the sup-ply voltage V and will in fact
sumptions are made with regard to the circuit. The tran
be determined solely by the collector current of tran
sistor and yoke inductance may be simpli?ed to a series
sistor T2.
inductance-resistance LR circuit and the ‘response to a
The stabilization of the collector current of T2 may be
step voltage E of 5 volts calculated. The total series re
accomplished by emitter degeneration by the inclusion of
sistance R3 is
35 resistor R3 in the emitter circuit. The potentiometer
Ohms
R2 serves as an amplitude control by establishing the DC.
Collector to emitter resistance _ _______ __, _________ __ 2
operating current in the collector circuit of transistor T2
Yoke resistance __
5
and hence the peak to peak sawtooth current of transis
Monitor resistance ___________________________ -_,.; 1
tOl‘ T1.
Modulation of the sawtooth current can be accom
8 40
plished by applying a modulating signal to the base circuit
The parallel combination of the 1 millihenry yoke
of T2, as explained, by use of a source 53 and transformer
and transformer is 900 microhenrysl The collector cur
50. The emitter degeneration serves to establish a
linear relationship between the modulated sawtooth cur
45 rent and the modulating signal.
Table 1, below, indicates the amplitude variations as
a function of frequency with and without the stabilization
and the time required to reach a collector current .of 200
circuit and indicates a measure of improvement obtained
ma. may be calculated from
with my present invention.
50
Table 1
scan interval.
.
Without
Stabilizer
(Point A
Frequency, kc.
55
'
grounded) ,
With stabi
liner Peak to
Peak Yoke
Peak to
Current, ma.
Peak Yoke
Current, ma.
=43 microseconds
now to FIG. 2E, it can be seen that the’
duration of the forward scan interval as shown by the
waveform is close to this value. The frequency of oscil 60
Referring
lation is conveniently controlled by the resistance R; in
the base-emitter circuit. Increasing the value of R1 re
duces the base current and therefore locates the knee in
8
'
16 ______________________________________ __
‘32
240
,180
175
180
70
180
I claim as my invention:
1. In combination a ?rst transistor having a base, an
emitter and a collector; an autotransformer; a resistor
the collector characteristic at a reduced current. The
connecting one end of said autotransformer to the base of
‘period of forward scan is reduced in response to an in 65 said ?rst transistor; a connection from the emitter of
crease of the frequency controlling resistance in the base
said ?rst transistor to an intermediate point on said auto
vemitter circuit.
transformen'an inductor having one end connected to
Undesirable changes in de?ection with changes in fre
the emitter of said ?rst transistor, means connecting the
quency of the de?ecting currents is due to the fact that
other end of said autotransformer to the other end of
the peak to peak current is a function of the saw-tooth 70 said inductor; a ?rst condenser connected between the
‘duration in accordance with the approximation
base of said ?rst transistor and the other end of said auto
ET
transformer; a second condenser connected between the
11:11:?
Wk}???
(.1 )
collector of said ?rst transistor and the other end of said
15 ill? V91tag6 across the yoke or inductance, L is 75 autotransformer; a unidirectional power supply; a second
3,070,758
5
transistor having a base, an emitter and a collector; means
for connecting the collector of said second transistor to
the other end of said autotransformer, means for connect
6
4. A stabilized sawtooth generator as de?ned in claim
3 wherein said current regulating means comprise a sec
ond transistor having its collector-emitter circuit con
nected in series with said inductive load and further in
ing said power supply between the collector of said ?rst
transistor and the emitter of said second transistor, and 5 cluding biasing means coupled between the base and
means for biasing the base of said second transistor with
emitter of said second transistor, said biasing means
respect to its emitter so as to cause constant average cur
controlling the average value of the current through said
rent to ?ow through said ?rst transistor whereby sawtooth
inductive load.
current pulses ?owing through said inductor will have a
5. A stabilized sawtooth generator as de?ned in claim
relatively constant peak to peak value over a range of 10 4 wherein modulation means responsive to an applied
operating frequencies.
signal is coupled to said biasing means, said modulation
2. In combination, a generator adapted for providing
means modulating the current through said inductive load
a sawtooth current to an inductive load, current regulat
in accordance with said applied signal.
ing means coupled in series with said inductive load, and
means coupling said series connected current regulating 15
References Cited in the ?le of this patent
means and said inductive load across the output of said
sawtooth generator, said current regulating means main
UNITED STATES PATENTS
taining the average current through said inductive lo-ad
constant.
2,847,569
Finkelstein __________ __ Aug. 12, 1958
3. A stabilized sawtooth generator comprising a tran
2,891,192
Goodrich ___________ __ June 16, 1959
sistor having an emitter, a base, and a collector, regen
2,897,429
Jochems ____________ __ July 28, 1959
erative feedback means connected betwen the base and
2,939,040
Isabeau ____________ __ May 31, 1960
emitter of said transistor; an inductive load connected to
the emitter of said transistor; current regulating means
OTHER REFERENCES
connected in series with said inductive load; and means 25
“Feedback-Stabilized Transistor Ampli?er,” by Slaugh
adapted for connecting a voltage source between said
ter in Electronics, May 1955, pages 174-175.
current regulating means and the collector of said tran
‘Electronics, by Herzog, May 1, 1959, pages 52—53.
sistor.
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