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