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Nov. 6, 1962
Filed March 24, 1959
United States Patent Of "are
Patented Nov. 6, 1962
Irving Horowitz, Eatontown, N.J., assignor to Blonder
Tongue Electronics, Newark, N.J., a corporation of
New Jersey
Filed Mar. 24, 1959, Ser. No. 801,629
3 Claims. (Q1. 330-12)
and will be more particularly pointed out in the appended
The invention will now be described in connection with
the accompanying drawing, FIG. 1 of which is a sche
matic circuit diagram illustrating the invention in simpli
?ed, preferred form; and FIG. 2 is a similar diagram
of the invention in a circuit embodying D.C. stabiliza
tion for temperature-controlling purposes.
Referring to FIG. 1, the vidicon or other substantially
The present invention relates to transistor ampli?er 10 constant-current source is illustrated as a generator 1 of
circuits, and, more particularly, to ampli?er circuits
a relatively broad band of frequencies, ranging from low
adapted for use with substantially constant-current signal
frequencies of the order of a few cycles, to high fre
sources, such as television vidicon pickup-devices, and
quencies of the order, for example, of seven and one-.
the like.
half megacycles. The source 1 is shown provided withv
In circuits employing vidicon and similar substantially 15 an effective internal high resistance 3 and an output
constant-current signal sources, it has been customary
to employ a large input resistance for the purpose of
capacitance Cx, illustrated in dotted lines. This source
1 is applied to an input transistor ampli?er stage 5, that,
generating relatively high voltages at low frequencies
in accordance with the present invention, and unlike
that may override microphonic noise generally produced
prior-art vidicon amplifying circuits and the like, is not
in the ?rst ampli?er stage. The use of such high input 20 of the emitter-follower type, but, rather, is of a normal
resistance, however, inherently makes it di?icult, ‘if not
impossible, to broad-band-peak the high frequencies.
grounded emitter amplifying type, though provided with
certain critical impedance relationships.
The stage 5
This is because the reactance of the input circuit ca
comprises the base 2, emitter 4 and collector 6.
pacitance is low compared to the load resistance to
In accordance with the present invention, there is con
obtain broad-band peaking. The art has thus had to 25 nected in the portion of the output circuits comprising
content itself with improvement of the signal-to-noise
the emitter-to-ground circuit, a resistance R2 that is
ratio at the low frequencies only. Inverse networks have
designed to have a value low compared with the base-to
been employed in subsequent circuits, however, to boost
emitter resistance RB, at the low frequencies of the band.
the high frequencies.
At the low frequencies, therefore, the product of the
This same approach has’ also been applied to transis 30 resistance R2 and the current gain [3 of the stage 5 repre
torized ampli?er stages for vidicons and other substan
sents the effective equivalent input resistance, so that
tially constant-current sources. The transistor, of course,
the input resistance has been raised from that value which
has a relatively low input resistance, so that it has been
would normally exist as a result of the inherent base-to
conventional to employ as the ?rst input stage from the
emitter resistance RB. A boosting of the low frequency
vidicon or other source, an emitter-follower stage having 35 voltages applied to the transistor is thus achieved, as is
a grounded collector. With an emitter~load resistor of
consequent improvement in the signal-to-noise ratio at
the order of, say, 1500 ohms, and a current gain B of
the low frequencies. At the high frequencies, however,
the order of 60, an effective input resistance of the order
the circuit acts as a normal grounded-emitter ampli?er.
of 90,000 ohms may be obtained for the low frequencies,
Shunting the resistor R2 is a capacitor C2 of a rather
providing low-frequency boosting.
40 critical value; namely, a value that presents a relatively
It has been found, however, that the noise produced
high impedance at the low frequencies, so that the resis
in the input transistor ampli?er stage substantially cor
tor R2 is the controlling element, and a relatively low
responds to that which would result if an equivalent
impedance to serve as a bypass at the high frequencies.
e?’ective noise generator were connected in series circuit
The stage 5, at the high frequencies, thus acts as a normal
with the base-to-emitter resistance, between the base and 4.5 ampli?er of the grounded-emitter type having a relatively
the emitter. If the impedance of the base-driving source
low input impedance.
becomes comparable to or greater than the base-to
Since the input capacitance of the transistor circuit is
emitter resistance itself, then such effective noise gen~
the sole effective impedance element, signal-wise, at the
erator exists between the base and emitter, irrespective
high frequencies, it is di?icult to attain the before-mew
of the value of emitter load resistance that may be con 50 tioned desired broad-band peaking in order to improve
nected in the circuit. Ampli?cation of noise results since
the signal-to-noise ratio at the high end of the band.
the circuit performs as a grounded-emitter ampli?er in~
But the input resistance RB of the transistor 5 decreases
sofar as the noise is concerned-and this, irrespective of
with increasing frequency. The present invention thus
whether the output load is disposed in the emitter or in
makes use of this phenomenon to obtain such broad
the collector circuit. The signal, however, will be de 55 band peakings at the high-frequency end by inserting,
generated in an emitter-follower stage, thus degrading the
preferably in series, a peaking inductance L, that reso
effective signal-to-noise ratio. Despite this fact, and
nates at the high frequency end with the output capaci
despite the lack of improvement at the high frequency
tance Cx of the substantially constant-current source 1,
end, these are the types of circuits that the art has had
and the input capacitance CB between the base 2 and
to employ heretofore in vidicon ampli?er stages and the 60 emitter 4 of the transistor 5. Such resonance preferably
is adjusted to occur near the cut-off region. In the
It is an object of the present invention to take advan
before mentioned example, this would be near seven and
tage of the above-mentioned understanding of the effec
one-half megaeycles. Through the utilization of this
tive positioning of the equivalent noise source, and to
peaking circuit, the high-frequency signals are also
overcome the difficulties inherent in such prior-art vidi 65 boosted, thus improving the signal-to-noise ratio at the
con or similar substantially constant current-source tran
high end of the band. The input peaking circuit acts as
sistor amplifying systems.
a transformer at high frequencies, matching the constant
A further object is to provide a new and improved
current source 1, 3, to the input of the transistor 5 by
transistor ampli?er circuit.
the ratio of CK to the larger input capacitance CB. The
Still an additional object is to provide a new and im 70 large L/ C ratio of the tuned circuit allows this to happen
proved vidicon amplifying circuit.
over a broad band of frequencies because the imped
ance of the tuned circuit is high over such broad band:
Other and further objects will be explained hereinafter,
The use of a relatively large peaking inductance L1
though providing a relatively low Q, provides a high
gain response over a broad band, thereby achieving the
desired end of broad-band high-frequency peaking.
What is claimed is:
1. An ampli?er for a substantially constant-current
source of a broad band of frequencies ranging from
relatively low to relatively high frequencies having, in
The capacitor C1 interconnecting the inductance L1
combination, a transistor ampli?er provided with at least
and the base 2 is merely a D.C-isolating capacitor. Bias
a base, an emitter and a collector, an input circuit con
current for the base 2 is provided from the negative ter
nected to the base and an output circuit connected be
minal B- of the current source, through resistor R1,
tween ground and the collector, means for connecting
and collector bias is supplied through resistor R3. The
the substantially constant-current signal source to the
output circuit is traceable from the collector 6 through 10 input circuit and comprising an inductance tuned with
the output conductor 8 and the ultimate load, not shown,
the inherent output capacitance of the source and the
and thence back through to the ground terminal 4’ of
base-to-emitter capacitance of the transistor to resonate
the emitter 4.
at a predetermined one of the said high frequencies, an
In FIG. 2, the system is shown in more complete form.
emitter load of impedance small compared with the base
The base bias network includes the further resistor R5 15 to-emitter input resistance at the said low frequencies,
to ground, and the D.C.-stabilizing resistor R4, inserted
and a capacitance shunting the said load and of high
in the emitter circuit to ground, with its by~pass capaci
impedance at the said low frequencies but low impedance
tor C3. The capacitor C2 then shunts both the resistors
at the said high frequencies.
R2 and R4. The value of the resistor R2 necessary to
2. An ampli?er as claimed in claim 1 and in which
obtain the above-described results will, in general, be 20 there is connected in circuit with the emitter load a
considerably smaller than the conventional value of the
direct-current stabilizing resistance of value greater than
resistor R4 employed for DC. stabilization. In a typi
the said load impedance.
cal circuit for use with a vidicon camera source 1, 3,
3. An ampli?er as claimed in claim 2 and in which
for example, a 2N384-type transistor 5 has been em
the said capacitance shunts both the said emitter load
ployed, with the following circuit values, obtaining the
improved perforance, before-described:
C1=.01 microfarads
R2=100 ohms
C2: 1000 micro-microfarads
C3=25 microfarads
R1=100K ohms
R3: 1000 ohms
R4=6.8K ohms
R5=68K ohms
Further modi?cations will occur to those skilled in
the art, and all such are considered to fall within the
spirit and scope of the invention, as de?ned in the ap
pended claims.
and stabilizing resistance.
References Cited in the ?le of this patent
Goodale _____________ __ Feb. 27, 1945
Wheeler ______________ __ Sept. 2, 1952
Eberhard _____________ __ Oct. 5, 1954
Van Overbeek ________ __ Nov. 5, 1957
Johnson _____________ __ Dec. 21, 1959
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