SURFACE-BARRIER TRANSISTOR

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03535A000500050002-8
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 9
• Document Creation Date: December 27, 2016
• Document Release Date: September 13, 2012
• Sequence Number: 2
• Content Type: MISC

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Declassified and Approved For Release 2012/09/13 :
CIA-RDP78-03535A000500050002-8
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Declassified and Approved For Release 2012/09/13 :
CIA-RDP78-03535A000500050002-8
Declassified and Approved ForRelease2012/09/13 : CIA-RDP78-03535A000500050002-8
/ I.
\._da
Pu11.4%
Amp
* All Video Crystals
with ?ca 25 to 40 micoAmp.
'forward bias.
*41 Surface-Barrier
Transistors
Form A is considered to be a video preamplifier system only.
Form B is considered to be a video preamplifier with sufficient gain to permit
direct audio monitoring and or recording with any conventional recorder/
amplifier system.
Form C 1 is the addition to form A of an transistor audio output (100 to 10000 cps)
power stage to permit full magnetic tape recording into standard magnetic
tape head (or Pierce 360 wire head).
Form C 2 is the addition to form A or B of sufficient transistor audio output
power stages to permit full magnetic recording into standard tape or -wire
head without utilizing the magnetic pulse amplifier stage. This Pnit
should consider video band pass low frequency cutoff of 20 kc as well
as 100 cps.
Pulse Input
DC Signal Control
input (Bias)
Load
GE Kagnetic Pulse Amplifier (Design Electronic Aug '54)
ibis,timiament Is part of mitigated
ditm If separated from the file it must le
filiblerdell to tadivideal systematic MAIM
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' Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
Surface-Barrier Transistor
The jurface-darrier transistor has great appeal to circuit application
eneineere, because it enables them to obtain the low-power advantages of junction
triode trensi3tors in many new aeilications. The high cut-off frequency of these
devices means iivt useable gain can n- ..r]fiv, in the very-elje-frseeonce range.
Further-gc , - te :e 'llgh cutoff fre,eenee ne low capacitance, these
ee'cee eake good video emilefiers.
Video Aeilifier!
One of the most int resting video-amplifier configurations is that in which
a number of similar steges are cascaded directly together. This ccndition is of
particular interest because it is not possible to employ transformer impedance match-
ing in a video amelifier. Furthermore, it has been found that the most efficient
use of transistors for tnis function is obtained by using a grounded-emitter
connection for all transistors. When this configuration is employed, the input
impedance of any etaee is equal to the load impedance of that stage, since the load
impedance is the input impedance of the next stage.
On the basis of the assumption of equal input and load impedances, the voltage
gain of a low-pass amplifier is equal to the magnitude of the current gain. The
bandwidth of such a stage will be determined by either the alpha cutoff frequency
of the collector capacitance. When the alpha cutoff is the limitation, and if it
is assumed that the frequency dependence of alph is like that of a single-section
low-pass filter, the gain-bandwidth product of a single stage is very nearly equal
to the alpha cutoff frequency of the transistor used in the stage. When collector
capacitance limits the bandwidth, the gain-bandwidth product is the reciprocal of
the product of the base resistance and collector capacitance, as in the case of
the tuned amplifier. The only difference is that, in tnis case, it may be necessary
to consider the low-frequency base resistance. For almost all Surface-Barrier
Transistors, the gain-bandwidth product due to collector capacitance is appreciably
higher than that due to alpha cutoff, and consequently is of little importance.
A two-stage video amplifier ueeing similar transistors having alpha cutoff
frequencies of approximately 50 mc., gave the performance shown in the attached figure
With all four coils in the circuit shorted, the bandwidth and transient response
were as shown in B, a bandwidth of 3.2 mc was obtained. The eain between the
1000-ohm source and the load impedance was 28 db. This gave a gain-bandwidth
product of 16 mc, per stage. This figure is lower than the predicted value of
50 mcs. for two reasons: First, the supply resistors dissipate some of the power
gain in the first stage. When shunt chokes were employed in series with these
supply resistors, to raise their impedance at the higher frequencies, the band-
width was increase to 6.5 mcs, as shown in C, giving a gain-bandwidth product
of 33 mc, for each stage. Second, the circuit and collector capacitances cause
some bandwidth limiting. Adding series peaking coils L3 and L4, in order to
resonate the collector capacitances, increased the bandwidth to 9 mcs., as shown
in D., and made the gain-bandwidth product equal to the theoretically predicted
value. Part C and D also show the resultant improvement in transient response.
Thus it is evident that, although the collector capacitance is not sufficiently
great to predominate in limiting bandwidth, it can have an appreciable effect,
?
Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
SMC
PRE-4VENCY
rime -1111.
D 4 ZASEC
Figure 6. Two-Stage Video Amplifier Using Surface-Barrier Tiansistbr-s
A. Sonpilf;ed Schematic and input Pulse
8. Frequency and TronslentResponse with All Four
Peaking Col Is Sherftd (Li = L2 ="1-0 L4 = 0E
C. Frequency and Transient Response unth L, and
in the Circuit a a 0)
b. Fruency and Tivntient atsponse with AII Four.
Pf&rinCo.Is4nU
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VIDEO AMPLIFIER NOTES:-
Amplifier Response & Gain -
Examination of the performance of a video amplifier requires a
determination of:
a. Maximum gain
b. Band width
c. The manner in which the video sensitivity varies for changes
in both input pulse length and pulse repetition frequency,
Amplifier maximum required response not directly related to recorder response.
a. Video sensitivity of an amplifier normally decreases as the pulse time
duration (width) becomes shorter and as the pulse repetition frequency
becomes less.
b. The reduction of sensitivity with pulses of shorter time duration is
a function of the ulimitedo bandwidth of the amplifier, in that amplifier
rise-time is not sufficient to allow the signal within the amplifier to
reach maximum amplitude before the end of the input pulse,
c. Average input power increases directly with the pulse repetition rate
of the signal.
d. The video bandwidth (within which the gain is not down more than
3 db from meadamm) required is from 20 cycles to 750kcs for optimum
sensitivity against pulses of about one microsecond duration. This amplifier
range provides an adequate rise-time and thus permits amplification of
short pus w.ith,AA. ;0...i,5.4ri sensitivity.
e* Effective average input power increases of low pulse repetition frequencies
can be accomplished when a means is provided for stretching the video output
from the video amplifier prior to amplifying it in the audio output stage
prior to recording. This stretching circuit must necessarily charge through
a low impedance in order to completely charge with4n the time-duration of
the signal, or there will be a loss in the amplitude of the output signal.
f. Associated redorder media frequently have a maximum response of
100 to 4000 cycles other recorder units permit increase frequency response
but only at a cost or weight, size and/or maximum duration of recording
time,
Compromise achievable*
Adequate amplifier band width permits a maximum possibility for maximum
complete amplification of pulses of short duration. Pulse stretching
then permits an effective increase of power output by increasing the
amplitude of the audio components of the signal, specifically the funda-
mental pulse repetition frequency and its lower harmonics falling within
the audio frequency response range of the operator or recorder.
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Video Notes:
Video amplifiers and pre-amplifiers can be designed to eliminate or greatly
reduce crystal noise through the low,-frequency cut-off characterisitics. Normally
this cutoff covers the audio range up to 20 ices. These units can not be employed
against continuous wave with voice-frequency modulations.
Video amplifiers and pre-amplifiers can be designed through the use of
larger bypass and coupling capacitors so as to permit receiption of audity,
modulations but will include considerable inherent crystal noise.
AN/PRR-6 video amplifier has a band pass from 20 kc to 1.7 mos, This permits
complete amplification of pulses of 0.25 microsecond duration.
Additional band-pass-can be incorporated in vacuum .tube units only at the
expense of battery life.
Video amplifiers canb e designed to permit adequate amplification to permit s
study and determination of both pulse width and pulse shape charatterisitice. The
useability of these features is dependent upon the associated equipments and methods
to be utilized in the actual measurment and determination of the wave shapes
envolved.
- Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
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Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
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Modification Proposal
1 September 511.
Featuring a possible addition to the Minifon modifications now encompassed within
framework of Shop Job No.TL:11:,2,
A possibility exists for the current modification being applied to the Minifon
recorder unit being made of greater operational potential through the incorporati
of a pulse-stretcher feature so as to obtain greater effective power where low
pulse repetition frequencies may be encountered.
Pulse stretcher to consist of three 1N69 crystals and an RC circuit comprising
R1 and the interelectrode capacity of the Hinifon DL-67 output tube found between
grid and ground.
?ases_of.positive polarity are applied to, and .pap?sed_bythe_lN69_arys,.
Since the intireI6bt-ivai-Cii5a.city-Orthe-CL=L7-is of ,comparatively small value
t chArges rapielly to the peak a-c voltage of the pulse..76;Ciii-WW7a the high
back impedance of-the-11469 crystaii; the iftferaiiirode capacity discharges
through R1, the high value of which (in the order of 2.5 to 3 megohms) slows the 1
rate of discharge. A sawtooth waveform with a shallow exponential trailing
edge thus .is producee and is applied to the grid of the DL-67 audio amplifier.
This causes the amplitude of the low-frequency components of the resultant wavefot
to be considerably increased, at the expense of the amplitudes of the high-
frequency components.
s.
------aince,these--low-frequency- components-fan 441AAl4n-the-audio--range-of---AATa-operator
/or recorder, and the high-frequency components do not, the .effective signal
power delivered to the output is increased. -
Block diagram
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Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
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Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
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Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8
Tiny Pulse Amplifier - A tiny, stable
signal levels, Was been developed by the
Preliminary tests indicate that drift is
-70?C to 1400C. The circuit diagram for
of the amplifier.
pulse amplifier ..t works at extremely low
General Electric CO., Schenectady 5, N.Y.
less than 10-"w over a temperature range of
the unit is shown below with a photograph
The amplifier is essentially a magnetic amplifier that uses a very small high-
permeability core and requires no rectifiers. The two greatest sources of drift
in conventional magnetic amplifiers - variation in rectifier and magnetic core
characteristics - have been eliminated in the pulse amplifier.
Drift problems in the conventional magnetic amplifiers are largely attributed to
forward rectifier drop reverse rectifier leakage, and variations in the magnetic
characteristics between cores. By eliminating the rectifiers, reducing the number
of operational cores to one per amplifying stage, and by operating this core in
push-pull, the pulse amplifier has considerably less opportunity for drift. The
circuitry is so devised that variation in saturation flux density and hysteresis
loop width have negligible effect. Changes in the hysteresis loop affect the gain
only, not the level of drift.
In operation, the magnetic core of the amplifier is driven into saturation by the
power pulses. Between pulses, the core magnetization settles back to a level
dictated by the control signal. The output power is determined by the amount of
pulse remaining after saturation. Push-pull operation is achieved, using a single
magnetic core, by comparing the alternate positive and negative pulses. Approximately
the same gain and speed of response are realized in the pulse amplifier as in the
conventional magnetic amplifier.
Basically a low-level device, the pulse amplifier can be used to amplify a signal
to the microwatt level. Here conventional amplifiers can be used to boost the
power to higher output levels without further effect upon the drift. The concept
of the pulse amplifier suggests a wide variety of new functions that may be performed
by magnetic amplifiers. These cover the fields of optical pyrometry, precision
calorimetry, spectroscopy, geophysics, meteorology, differential thermometry, etc.
Wherever extreme sensitivity is desired, the pulse amplifier has an application.
Materials used to make the cores of the pulse amplifier are the same as those used
in conventional magnetic amplifiers - silicon steel, nickel-iron alloy, permalloy,
Mumetal, etc.
Declassified and Approved For Release 2012/09/13: CIA-RDP78-03535A000500050002-8