Integrated injection logic (IIL, I
2L, or I2L) is a class of
digital circuits built with multiple collector
bipolar junction transistor
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipola ...
s (BJT). When introduced it had speed comparable to
TTL
TTL may refer to:
Photography
* Through-the-lens metering, a camera feature
* Zenit TTL, an SLR film camera named for its TTL metering capability
Technology
* Time to live, a computer data lifespan-limiting mechanism
* Transistor–transistor lo ...
yet was almost as low power as
CMOS, making it ideal for use in
VLSI
Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) c ...
(and larger)
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s. The gates can be made smaller with this logic family than with CMOS because complementary transistors are not needed. Although the logic voltage levels are very close (High: 0.7V, Low: 0.2V), I2L has high noise immunity because it operates by current instead of voltage. I2L was developed in 1971 by
Siegfried K. Wiedmann and
Horst H. Berger
Horst H. Berger (born March 30, 1933) is a German electrical engineer noted for his contributions to semiconductor technologies for integrated circuits.
Berger was born in Liegnitz (Legnica), Lower Silesia, and received the Vordiplom. from the T ...
who originally called it merged-transistor logic (MTL).
[
]
A disadvantage of this logic family is that the gates draw power when not switching unlike with CMOS.
Construction
The I2L inverter gate is constructed with a
PNP common base current source transistor and an
NPN common emitter open collector inverter transistor (i.e. they are connected to the GND). On a wafer, these two transistors are merged. A small voltage (around 1 volts) is supplied to the emitter of the current source transistor to control the current supplied to the inverter transistor. Transistors are used for current sources on integrated circuits because they are much smaller than resistors.
Because the inverter is open collector, a
wired AND operation may be performed by connecting an output from each of two or more gates together. Thus the
fan-out
In digital electronics, the fan-out is the number of gate inputs driven by the output of another single logic gate.
In most designs, logic gates are connected to form more complex circuits. While no logic gate input can be fed by more than one ...
of an output used in such a way is one. However, additional outputs may be produced by adding more collectors to the inverter transistor. The gates can be constructed very simply with just a single layer of interconnect metal.
In a discrete implementation of an I2L circuit, bipolar NPN transistors with multiple collectors can be replaced with multiple discrete 3-terminal NPN transistors connected in parallel having their bases connected together and their emitters connected likewise. The current source transistor may be replaced with a resistor from the positive supply to the base of the inverter transistor, since discrete resistors are smaller and less expensive than discrete transistors.
Similarly, the merged PNP current injector transistor and the NPN inverter transistor can be implemented as separate discrete components.
Operation
The heart of an I2L circuit is the common emitter open collector inverter. Typically, an inverter consists of an NPN transistor with the emitter connected to ground and the base biased with a forward
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
from the current source. The input is supplied to the base as either a current sink (low logic level) or as a high-z floating condition (high logic level). The output of an inverter is at the collector. Likewise, it is either a current sink (low logic level) or a high-z floating condition (high logic level).
Like
direct-coupled transistor logic
Direct-coupled transistor logic (DCTL) is similar to resistor–transistor logic (RTL) but the input transistor bases are connected directly to the collector outputs without any base resistors. Consequently, DCTL gates have fewer components, ar ...
, there is no resistor between the output (collector) of one NPN transistor and the input (base) of the following transistor.
To understand how the inverter operates, it is necessary to understand the current flow. If the bias current is shunted to ground (low logic level), the transistor turns off and the collector floats (high logic level). If the bias current is not shunted to ground because the input is high-z (high logic level), the bias current flows through the transistor to the emitter, switching on the transistor, and allowing the collector to sink current (low logic level). Because the output of the inverter can sink current but cannot source current, it is safe to connect the outputs of multiple inverters together to form a wired AND gate. When the outputs of two inverters are wired together, the result is a two-input NOR gate because the configuration (NOT A) AND (NOT B) is equivalent to NOT (A OR B) (per
De Morgan's Theorem
In propositional logic and Boolean algebra, De Morgan's laws, also known as De Morgan's theorem, are a pair of transformation rules that are both valid rules of inference. They are named after Augustus De Morgan, a 19th-century British mathem ...
). Finally the output of the NOR gate is inverted by IIL inverter in upper right of the diagram, the result is a two-input OR gate.
Due to internal parasitic capacitance in transistors, higher currents sourced into the base of the inverter transistor result in faster switching speeds, and since the voltage difference between high and low logic levels is smaller for I2L than other bipolar logic families (around 0.5 volts instead of around 3.3 or 5 volts), losses due to charging and discharging parasitic capacitances are minimized.
Usage
I2L is relatively simple to construct on an
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
, and was commonly used before the advent of
CMOS logic by companies such as
Motorola
Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent public companies, Motorol ...
(now
NXP Semiconductors) and
Texas Instruments
Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...
. In 1975,
Sinclair Radionics
Sinclair Radionics Ltd was a company founded by Sir Clive Sinclair in Cambridge, England which developed hi-fi products, radios, calculators and scientific instruments.
History
After raising funds to start the business by writing articles ...
introduced one of the first consumer-grade digital watches, the
Black Watch
The Black Watch, 3rd Battalion, Royal Regiment of Scotland (3 SCOTS) is an infantry battalion of the Royal Regiment of Scotland. The regiment was created as part of the Childers Reforms in 1881, when the 42nd (Royal Highland) Regime ...
, which used I2L technology.
In 1976, Texas Instruments introduced
SBP0400 CPU which used I2L technology.
In the late 1970s, RCA used I²L in its CA3162 ADC 3 digit meter integrated circuit. In 1979, HP introduced a frequency measurement instrument based on a HP-made custom LSI chip that uses integrated injection logic (I2L) for
low power consumption and high density, enabling portable battery operation, and also some emitter function logic (EFL) circuits where high speed is needed in its HP 5315A/B.
["HP memory project: Time, Frequency Standard & Counter"]
References
Further reading
*
{{DEFAULTSORT:Integrated Injection Logic
Logic families