IEEE SSCS Distinguished Lecture on "Design of Ultra low distortion Band pass Filters and Sinusoidal Oscillators"
IEEE SSCS Kolkata Chapter has successfully organized a Distinguished Lecture Program on 1st April. 2023. Prof. Nagendra Krishnapura, Department of Electrical Engineering, IIT Madras has delivered the lecture on “Design of Ultra low distortion Band pass Filters and Sinusoidal Oscillators”. The Event was held virtually on WebEx platform from 3.30 pm on 1st April, 2023.
Abstract of the Talk
Histogram test and THD measurement of high resolution( 18 to 20 bits) ADCs require a sinusoidal source with THD 140 dBc Bench top generators can be used, but they are bulky The alternatives are to use a band pass filter to clean up a medium accuracy(~ 80 dBc) sinusoid from a DAC or to use a sinusoidal oscillator In either case, a very low distortion filter core is essential This work investigates techniques for realizing ultra low distortion band pass filters and sinusoidal oscillators
Active RC filters have a very low distortion because nonlinearities can be suppressed using a high loop gain The main sources of distortion in an active RC bandpass filter are ( The nonlinearity of the output stage of the opamp used in the active filter coupled with the capacitance at the input of that stage This is suppressed using a buffer between the first and the second stage of the opamp ,,( distortion contributed by passive components(integrating capacitors) in the feedback loop that is not suppressed by the loop gain This is mitigated using distortion cancellation, and ( output conductance nonlinearity of the opamp This is suppressed using a gain boosted cascode output stage In oscillators, an additional distortion source is the modulation of the oscillator’s loss by the ripple in the output of the amplitude stabilization loop that is required for stable sinusoidal oscillations A four phase full wave rectifier combined with second order ripple filtering minimizes this effect
Using the principles above, low distortion band pass filters and sinusoidal oscillators are demonstrated in a 0 6 μm process With a 5 6 V supply, the 1 kHz/ 10 kHz band pass filter prototype has 60 dB HD 2 attenuation and 143 dBc/ 142 dBc THD for a 10 Vppd output The 1 kHz/ 10 kHz oscillator has 133 dBc/ 111 dBc THD for a 10 Vppd output.
More than 60 Student/Faculty/ Research Scholar/Industry professionals participated in the event. Lecture created lots of interest among the participants. Prof. Krishnapura answered all the queries from the participants after the talk. IEEE SSCS Kolkata chapter will organize more such events in future.
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Prof. Nagendra Krishnapura of Indian Institute of Technology, Madras, India
Design of Ultra low distortion Band pass Filters and Sinusoidal Oscillators
Biography:
Prof Nagendra Krishnapura obtained his B.Tech from the Indian Institute of Technology, Madras, India and his PhD from Columbia University, New York. He has worked as an analog design engineer at Celight, Multilink and Vitesse semiconductor. He has taught analog circuit design courses at Columbia University as an adjunct faculty. He is currently a professor at the Indian Institute of Technology, Madras. His interests are analog and RF circuit design and analog signal processing
Address:Department of Electrical Engineering, IIT Madras