1. Hall Effect Current
Sensor using
Transconductance
Amplifier
J Sudheer Kumar
Thesis Supervisor: Dr. P. Sensarma

2. Outline
 Introduction
 Closed loop Hall effect current sensor
operation
 Compensator Design
 Transconductance Amplifier design
 Results
 Conclusion and future scope
 Experimental setup
 References

3. Introduction
 Aim is to design a current transducer which provides
good linearity and accuracy at large currents with
adequate bandwidth
 Current sensing techniques
 Ohm's law of resistance – Shunt resistors and trace
resistors etc.
 Faraday's law of induction - Current Transformers
etc.
 Magnetic field sensors – Hall sensors, Fluxgate
sensors etc.
 Faraday effect – Polarimeter detection method etc.

4. Current Transformer Operation

5.  Using both the principles of the current
transformer and closed loop Hall element
current sensors, a modified Hall effect
current transducer can measure both DC
and high frequency currents
 Indium antimonide (InSb) have ultra-high
sensitivity.
Hall Element

6. Closed loop Hall effect current sensor

7. Plant transfer function

8. Model of the complete plant

9. Compensator Design
 Low Frequency Model:

10.  corner frequency is at 14.6 rad/s

11.  High Frequency Model:

12. Tuning the compensator
 uniform gain throughout all the frequencies is ensured by Kp = 2:59

13. Limitation

14. Realization with op-amps
Hall element Control current
Circuit
 Kp = 2.59 and Ki = 37.8

15. Transconductance Amplifier
Design
 Why MOSFET?

16. MOSFETs in parallel operation

17. MOSFET as an amplifier
 Cross-over Distortion

18. Amplifier with matched pair

19. Operation under signal
conditions

20. Drawbacks with matched pair Amplifier
 output current is unsymmetrical
 Negative feedback of output voltage

21. Schematic of Complete
Transconductance Amplifier

22. Limitation of supply voltage

23. Closed loop circuit

24. Results
Waveforms of amplifier for 160mA output current at
15kHz
Signals of amplifier at peak output current of
130mA at 100 kHz
Frequency THD of
Input (%
of fund)
THD of
Output (%
of fund)
150 kHz 0.5621 3.1107
100 kHz 0.4132 2.0171
70 kHz 0.5810 1.6605
2 kHz 0.6726 0.9408
100 Hz 0.6572 0.7727
5 Hz 0.5795 0.8251

25. Response to
input signals
 Response to
50Hz signal
 Step Response

26. Linearity test results
 DC current measured is varied
from -200AT to 200AT

27. Experimental setup

28. Experimental setup – Complete circuit

29. Experimental setup –
Transconductance Amplifier

30. Conclusion
 Mathematical modeling of each of these is
subsequently presented to arrive at an overall plant
model
 A feedback (closed-loop) controller is then
systematically developed to realize a at pass-band
characteristic
 Two possible circuit realization approaches, based
on matched-pair and identical devices, are
presented
 An experimental circuit is fabricated and the
results obtained are presented for evaluation

31. Scope for Future Work
 Bootstrap Circuit to push op-amp rail voltage
Overcome the problem of limited op-amp
rail voltage by using the output voltage to increase
the rail voltage of the op-amp
 Overdrive circuit for high frequency operation
MOSFET enters into ohmic region of operation

32. References
 S. Ziegler, R. C. Woodward, H.-C. Iu, and L. J. Borle, “Current
sensing techniques: A review”, Sensors Journal, IEEE, vol. 9, no. 4,
pp. 354 -376, 2009.
 D. Halliday, R. Resnick, and J.Walker, Fundamentals of physics
extended. John Wiley & Sons, 2010.
 A. S. Sedra and K. C. Smith, Microelectronic Circuits Revised Edition.
Oxford University Press, Inc., 2007.
 R. P. Feynman, R. B. Leighton, and M. Sands, The Feynman Lectures
on Physics, Desktop Edition , vol. 1. Basic Books, 2013.
 A. Kumar and V. John, “Compensator design for closed loop hall-
effect current sensors,” Sixth National Power Electronics Conference
IIT Kanpur, India, Dec 20-22 2013.
 Je Pankau, David Leggate, D Schlegel, R Kerkman, and G Skibiniski.
“High frequency modeling of current sensors,” in Applied Power
Electronics Conference and Exposition, 1999. APEC'99. volume 2,
pages 788-794.

33. Thank you!