December 13, 1965 Electronics
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Electronics,
published 1930 - 1988. All copyrights hereby acknowledged.
The December 13, 1965 issue
of Electronics magazine was largely dedicated to assessing Japan's status in the
electronics industry. Japan, with the help of the United States, made a remarkable
recovery from defeat during World War II to have become an emerging power in
electronics. "Made in Japan" labels on products had transformed from being the butt
of jokes because of pre-war low quality products to representing assurance of low
cost, high functionality and high value products. It still does to this day. The
Japanese people have worked hard to acquire the world's respect as smart innovators
and hard workers, and have been sure to maintain manufacturing bases within their
borders. When you read this article, be prepared for a few dated terms like a "Kita" diode, having gigahertz (GHz) presented as gigacycles
(Gc), decibels abbreviated as "db" rather than "dB," intermediate frequency given
as "i-f" instead of "IF," and "polyiron" which if you look it up, nowadays refers to vitamin
supplements rather than iron metal alloys.
Japanese Technology - Bidding for World Leadership in Solid State
Isao Someya is chief of the director's office at the Electrical Communications
Laboratory in charge of planning. He is a 1938 graduate of Tokyo University and
earned his doctorate degree from the university in 1951.
With problems uniquely suited to solution by microwave, the Japanese are making
big advances in solid state equipment using such components as the tunnel diode,
Kita diode, hyperabrupt diode and mesa transistor
By Isao Someya
Electrical Communication Laboratory
Nippon Telegraph and Public Corp.
Japan has many of the problems that microwave is best-suited to solve - communications
needs of a dense population (about half that of the United States squeezed into
an area smaller than Montana), a combination of mountainous terrain and narrow streets
that make coaxial cable difficult to install and maintain, and expensive and limited
natural power. Japan also had an "advantage" - a chance to start fresh after 80%
of its telephone service had been destroyed during World War II.
For these reasons, the country chose microwave and today has the densest system
in the world. Japan's first solid state microwave system went into operation in
1962, an 11-gigacycle system that connected television studios to telephone exchanges
a short distance away. The system required only 10% as much power as would a comparable
tube setup, and construction costs were halved. Because of these savings, Japan
developed solid state systems and today boasts that her solid state microwave gear
is as good as any in the world.
Although Japanese engineers borrow heavily from United States technology, they
have made significant contributions in the microwave field, primarily with the application
of Japanese-developed components such as the tunnel diode and the Kita diode. Since
there are no military programs to prime the research pump in Japan, most of the
development has been done at the Electrical Communication Laboratory of the government-owned
Nippon Telegraph and Telephone Public Corporation. Its laboratory is comparable,
in a modest way, to the Bell Telephone Laboratories. More recently, development
work of this type has also been carried on in the research laboratories of a few
private companies; the Nippon Electric Co., Fujitsu Ltd., Hitachi Ltd., Mitsubishi
Electric Corp. and Toshiba (Tokyo Shibaura Electric Corp.).
New baseband repeater for solid state 2 Gc system. Transmitter-frequency
mixer (color) supplies 300 mw output.
In parametric amplifier for 4-Gc system, d-c biasing voltage
is fed through the circulator and polyiron non-reflecting termination. Pump power
is supplied by a tripler which multiplies the output of the transmitter local oscillator.
When pump power changes, variation of gain in parametric amplifier
for 4-Gc system is small.
Characteristics of low noise amplifiers for 4 Gc system.
Frequency modulator (top), with four abrupt junction diodes (shown
in color) in tuning circuit has linear output. Linearity, bottom, is within 1% over
range of 70 Mc ±8.
Microwave repeater stations, like this one at Futago Yama, dot
the hilltops of the Japanese countryside. Inside the building is a heterodyne repeater.
Block diagram of local oscillator in broadband repeater for 6
Gc system has a crystal oscillator, transistor amplifiers and multipliers. Narrow
bandpass filter, composed of two stages of cavity resonators operating in the H021
mode, reduces undesired harmonics and noise.
Switching circuit with Kita diodes has transition time of 15
to 20 nanoseconds for break and 40 nanoseconds for restoration. That is more than
adequate, even for high-speed data transmission of 1,000 to 2,000 bands for which
a transition time of 40 microseconds is required.
Specifications for varactor diode in high power multiplier.
Once a development is perfected, the Electrical Communication Laboratory (ECL)
turns the design over to one or more manufacturers. The Japanese success in competing
in the international market is evident in the sales of microwave equipment to the
governments of Mexico, Taiwan, and Indonesia.
Solid state research in the microwave field in Japan can be traced to 1955 when
the concept of the parametric amplifier was proposed independently at ECL. From
this proposal came the development of variable capacitance diodes (varactors) and
silver-bonded or Kita diodes. Mesa transistors with gain-bandwidth products of several
hundred megacycles were developed in 1959. Today in Japan, parametric amplifiers
are used mainly in over-the-horizon systems of medium capacity operated by private
users such as railroads and utility companies. NTT has used these amplifiers in
a 2-Gc over-the-horizon system that connects the southern island of Kyushu to Okinawa.
And the applications are increasing as the microwave networks grow.
Last March, NTT tested a new all-solid state 2-Gc system. First units of this
UF-B4 system are being installed now, and are scheduled to be operating before the
end of the year. Designed for short telephone circuits where branching is frequent,
the UF-B4 generally uses a baseband repeater (see block diagram above) but can also
use a heterodyne repeater for long-distance systems.
One of the most interesting parts of the repeater is the transmitter-frequency
mixer, which supplies the 300-milliwatt output of the transmitter. A local oscillator
of the frequency-multiplier type delivers about one watt to the mixer. In the transmitter
converter, a 70 Mc carrier that has been frequency-modulated by the baseband signal
is heterodyned against the transmitter's local oscillator to produce the transmitter
output signal. Power loss of about 5 decibels in the transmitter mixer accounts
for the difference between the one-watt frequency-multiplier output and the 300-milliwatt
As a baseband system, the modulator is connected to the last i-f amplifier, which
is sometimes called the post-i-f amplifier, so that the signal is amplified to the
high level required at the transmitting mixer. When the mixer is to be used as a
heterodyne repeater, the output of the receiver main i-f of half the repeater is
connected to the last i-f amplifier of the transmitter of the other half. In this
configuration, the receiver demodulators and transmitter modulators are not used.
The power consumption of a repeater in this 2-Gc system is about 100 watts. The
standard repeating span is about 31 miles. If the span loss is large, NTT inserts
a tunnel-diode amplifier with a gain of 15 db and a noise figure of 5 db on the
front-end of the receiver. In the 70 Mc modulator, hyperabrupt junction diodes are
the modulating elements.
While one section of ECL is designing systems, another section works on components.
One major area of research has been in low-noise amplifiers.
At present, the laboratory considers only the parametric amplifier, operating
at room temperature, and tunnel-diode amplifiers practical for broadband microwave
systems. Maser and parametric amplifiers, which operate at the temperature of liquid
helium, are so expensive and difficult to maintain that NTT considers them unsuitable
for first-stage amplifiers of broadband systems.
So far in NTT's networks, parametric amplifiers have been used commercially only
in the over-the-horizon system between Kyushu and Okinawa. The amplifiers are placed
in the front ends of the receiver for this link's two operating bands: 900 Mc for
television and 2-Gc for multichannel telephone transmission.
A similar amplifier has been designed for a 4 Gc broadband system (see figure
next page) that can handle 960 telephone channels. The doc biasing voltage, which
is applied to the varactor diode, is fed through the circulator and polyiron non-reflecting
termination. Coaxial lines are tuned by inserting dielectric plungers.
Pump power for the amplifier, 10 to 20 milliwatts at 12 Gc, is supplied by a
tripler which multiplies the output of the transmitter local oscillator. As pump
power changes, variations in gain characteristics of the amplifier are small (see
p. 103). Because of the design, automatic control of the pump power is unnecessary;
this simplification is made possible primarily by the characteristics of the device:
an optimum self-bias voltage for the diodes and suitable detuning of the resonance
circuit. These characteristics eliminate variations in the bandpass characteristics.
In 1963, research started on an 11-Gc parametric amplifier built with silver-bonded
diodes. These diodes are a unique Japanese development, devised by Shoichiro Kita
at ECL in 1955. Many types of these devices are now made in Japan for parametric
amplifiers, microwave switches, transmitter converters for repeaters and i-f limiters.
Because of its Kita diodes, the 11-Gc amplifier had a very low noise figure: 3 db
measured for sideband reception at room temperature and 0.7 db at 85°.
The other low-noise amplifier favored by the Japanese is a tunnel-diode type.
This amplifier is not suitable for systems operating with relatively high input
lines, because its saturation level is low. This restriction can be removed if tunnel
diodes with high negative conductance are chosen.
For example, in the receiver of a 4-Gc broadband system, a tunnel-diode amplifier
has a noise figure only slightly worse than a parametric amplifier. But it has one
big advantage: it can amplify microwaves without requiring pump power.
When the Japanese became acquainted with variable capacitance diodes or varactors,
they began using them in frequency multipliers.
NTT uses such a frequency multiplier as a local oscillator when the required
output power of the oscillator is low and the frequency is 6 Gc or less. Under these
operating conditions, the solid state multiplier has a higher efficiency (defined
as the ratio of microwave output to the doc power input) than the conventional klystron
oscillator. In addition, NTT has found that the longer life of a diode and the elimination
of complicated automatic frequency control circuits simplify maintenance. In the
SF-U2 system - NTT's second-generation 6-Gc system - only the local oscillator is
solid state. Its output is only 20 dbm (20 db above 1 milliwatt or 100 milliwatts).
But in the newest 6-Gc system, the SF-U3 - scheduled for field test in 1966 and
for installation in 1967 - all vacuum tubes are replaced by transistors.
The local oscillator in this new system (see block diagram p. 104) has a crystal
oscillator, transistor amplifiers and multipliers. Operating at a frequency between
55 and 59 Mc, the crystal oscillator is an overtone type.
The input to the frequency multiplier has a frequency-modulated noise component.
Because its frequency deviation is multiplied by a factor of 108, parasitic oscillations
have to be suppressed and noise reduced in the crystal oscillator and power amplifiers
that follow. To reduce undesired harmonics and noise, a narrow bandpass filter -
composed of two stages of cavity resonators operating in the H021 mode
- has been inserted in the output of the multiplier. The loaded Q of the filter
is about 8,000 and its insertion loss is about 2 db.
ECL also has developed a new frequency multiplier for the new all-solid state
4-Gc system. In this multiplier, the overtone crystal oscillates at 114 Mc, This
signal is amplified to about 30 watts before two tripler stages increase the frequency
to 1,025 Mc.
The last two multiplier stages are doublers. They are made with a special varactor
diode, the ECL 1242, which has an output of 2.5 watts at 4 Gc (see table p. 105
for its characteristics). Thus, the power range of the multiplier varies from an
input of 30 watts at 114 Mc to an output of 2.5 watts at 4.1 Gc.
Improvements in solid state i-f amplifiers have made it possible to design better
solid state repeaters. A solid state i-f amplifier was used first in 1961 in the
first-generation 11-Gc system. Its bandwidth was large enough to amplify 600 telephone
channels. Better transistors and transistor circuitry boosted this capability to
1,800 telephone channels and such an amplifier is now in production. ECL also has
almost completed work on an improved amplifier that can handle 2,700 telephone channels
- more than quadrupling capacity in 4 years.
Low-Noise Parametric Amplifier
A key performance characteristic is output voltage. The output voltage of the
i-f amplifier, designed for the repeater of the new solid state 4-Gc system, is
90 volts into a load of 500 ohms in parallel with 10 picofarads. This is a desirable
performance for a heterodyne-type repeater, which requires a large i-f amplifier
output supplied to the transmitter frequency mixer. In addition, a large i-f input
decreases the microwave loss between the input of the local oscillator and the output
of the transmitter frequency mixer. The new i-f amplifier has a frequency characteristic
which deviates less than 0.2 db at 70 Mc + 10 Mc.
Another component that has made an important contribution to microwave technology
in Japan is the hyperabrupt junction diode, which has made possible solid state
The useful characteristic of a hyperabrupt junction diode is the value of n in
the equation for junction capacitance:
Cj = (Ck)/(φ
where Cj = junction capacity
Ck = a constant
V = bias voltage supplied to diode
φ = contact potential
Usually, n is larger than 1/2 and sometimes is as large as 5 or 6.
If a diode with an n value of about 2 is placed in the tuning circuit of the
modulating oscillator and its bias voltage is controlled by the input signal, its
linearity is good enough so the oscillator can modulate a super multi-channel signal.
Under these conditions, the variation of differential modulation is less than 1%
in the range of 70 Mc + 4 Mc. Sensitivity is more than 10 Mc per volt.
Also, when several diodes are connected in parallel and are given different bias
voltages to compensate for the characteristics of each, linearity can be improved
to cover a broader range of frequency deviation. One modulator designed this way
used 4 hyperabrupt junction diodes (see figure p. 104) and its variation of differential
modulation was less than 1% in the range of 70 Mc ± 8 Mc (see figure below
circuit on p. 104).
Solid State Switching
Traditionally, the reed relay has been used for switching an r-f channel to a
protection channel when there is equipment failure or severe fading. The transition
time of these mechanical devices is 1 to 2 milliseconds. Since this time is barely
satisfactory for the transmission of 50-band telegraphy, it is clearly unsatisfactory
for high-speed data transmission. Therefore, ECL has developed a solid state unit,
using Kita diodes, for the 11-Gc system and the unit can be used in the new 15 Gc
system, too. The actual design goes back to 1959, even though it has been used only
When such a switching circuit (see figure above) is used in the receiving side
of a broadband telephone system, the distortion introduced by the diodes which are
positively biased, must be kept small. The impedance ratio of reverse-biased diodes
to positive-biased diodes determines the quantity of cross talk between switched
The insertion loss of this circuit is less than 0.6 db. The transition time is
about 15 to 20 nanoseconds for break, 40 nanoseconds for restoration. These times,
which include the operation times of the driving circuits, are more than adequate
because the transmission of high-speed (1,000 to 2,000 band) data requires a transition
time of about 40 microseconds.
To extend solid state in microwave, researchers in Japan are concentrating on
developing power transistors and varactor diodes that can handle the higher frequencies
at higher powers. The biggest obstacle is not system design, but lack of understanding
of the diffusion technology for producing such devices.
Posted July 18, 2019