Transcript
TRANSLINEAR CIRCUITSNaveen KumarTarun KumarAnubhav Anand
Guide: Dr. V.K. Singh Co-guide: Er. Ashok Kumar
Contents• History• What is Translinear?• Translinear Cells• Modern usage of the word• General Principles• Translinear Loop/Network• Translinear Principle• Application of Translinear Principle• Extended Translinear Theory• Effect of Device non idealities• Conclusion
History•The word translinear (TL)
was invented by Barrie Gilbert in 1975 to describe circuits that used the exponential current-voltage relation of BJTs
• Concept arose within the con- text of ‘gain cells’ for use in oscilloscopes.
What is Translinear?• Used of those cells invoking
exponential device behaviour• Applies to all BJTs, and MOS
transistor operating in sub threshold region
• Everyday use in analog multipliers, variable-gain cells, filters, RMS converters and many other nonlinear circuits.
• Strictly TL(just TL) in BJTs and Voltage Translinear in MOS Transistors
Translinear Circuit Types•Translinear Cells are categorised as TL cells
and TN cells on the basis of network topology
•TL Cells are Translinear Loops•TN Cells are characterized by having
multiple emitters tied to a common node and biased by one current
•TN Cells are the Translinear cell network• A TL Cell can be an integral part of TN Cell
TN Cells Vs. TL Cells A Translinear Network but not a Translinear Loop
Characteristics of TL Cell• Use of monolithically integrated bipolar junction
transistors (BJTs)• Simple and elegant, being largely comprised of DC-
coupled BJTs and current sources• Arranged in closed loops, each containing at least
two base-emitter junctions • Variables-the cell inputs, outputs and control biases
are all in current-mode form.• Operation at very low supply voltages was possible• squaring; square-rooting; multiplication and
division; multi-dimensional vector addition and subtraction;
Modern Usage of the Word•Seevinck and Wiegerink have stretched
the idea of translinearity even further•JFETs and MOSFETs in strong inversion
exhibit a Voltage Translinearity• Transconductance is a linear function of
the gate-source bias Vgs, starting with the popularly-assumed quadratic relationship
General Principles• The basic starting point is the
exponential relationship of BJT’s collector current and base emitter voltage
• And also
• The collector current will vary enormously even for fixed base emitter voltage• A TL circuit is quite immune to
this immense variation in current
Translinear Loops•Function depends primarily on the use of
current as signals•Arranged in one or more closed loops•Augmented by various biasing means.•Nevertheless, such circuits can be quickly
understood when the Translinear Principle is applied
•Example- A simple Current Mirror
Translinear Network•BJT circuits such as LNAs, differential
pairs, CML and ECL logic gates, multi-tanh transductors
•These circuits have no closed loop junctions
•But transconductance (or transresistance) of the transistors is of crucial importance
•A differential pair is general example of a translinear network.
The Translinear Principle•a
Application of TL Principle•Using translinear Principle
the vector sum can be shown to be achieved easily
Extended TL Theory•In basic TL circuits, this ratiometric
behaviour arises from setting the net loop voltage to zero.
• However, it is certainly possible, and occasionally even useful, to include one or more voltage sources in a loop, when the governing equation becomes
• A practical use of such a voltage is to null out the 'VBE mismatch' in a TL loop
The Ratiometric Viewpoint•The advantage of this viewpoint is that
one does not need to worry about the absolute value of the currents
Effect of Device nonidealities•There are various nonidealities in the BJT
operation•The value of base emitter voltage used in
(2.1b) assumes a base collector voltage of zero which is not such
•The current gets modified by a factor of• There are no general solutions to
dilemmas of this sort, but they usually can be worked around
Conclusion•The 'voltage- controlled current-source' view
of the BJT, which is captured in the notion of 'translinearity', is a more useful one than the older idea of a 'current-controlled current source' (the 'beta view') in a modern monolithic context.
• Largest utilization of translinear concepts has been in the area of analog multiplication.
• 'MOS-translinear' (MTL) circuits are Voltage translinear circuits.
Thank You
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