Envelope-Tracking Supply Modulator with Trellis Search-Based Switching and 160MHz Capability

Speaker: Weiyu Leng
Affiliation: Ph.D. Candidate

Via Zoom Only: https://ucla.zoom.us/j/91696217830

Abstract: Envelope tracking (ET) is in wide use to raise the efficiencies of PAs. It operates on the principle that if PA’s supply voltage tracks the RF waveform’s envelope, the PA will operate in saturation all the time, and therefore at its peak efficiency. A practical realization brings up many problems, chief being the realization of an envelope-tracking supply modulator (ETSM), whose own efficiency must be as high as possible. A hybrid amplifier is commonly used, which, in effect, partitions the envelope bandwidth into a low and high subband. An efficient switching buck converter tracks the low band, which contains most of the load current. In parallel with it, an op amp with a Class-AB output stage supplies the current in the high band. Feedback servos the total current to the envelope waveform extracted from the baseband modulator.

In prior art the HA is realized with feedback using a hysteresis comparator, whose output actuates the two switches of the buck converter to respond to the changing envelope; the continuous-time op amp makes up for the error. But a buck converter driven by a comparator that reacts to the instantaneous waveform produces a slew-rate limited current that, like a slewing op amp, always lags the envelope waveform. This forces the op amp to produce a larger current to correct the error, and the arrangement cannot guarantee that the buck converter switches no often than is absolutely necessary. We replace the hysteresis comparator with a novel trellis-search that, first, finds the optimal sequence to switch the buck converter to minimize the RMS current that the op amp must deliver; second, to lower loss from switching capacitance of FETs, it penalizes a large number of switching events in the buck converter. The Viterbi-like search is optimal. Meanwhile, bypassing the DSP and replacing it with an on-chip hysteresis comparator to realize a conventional HA, we can demonstrate ETSM operation up to 160 MHz modulation bandwidth. This is the widest bandwidth reported so far for any ETSM.

Biography: Weiyu Leng is a Ph.D. candidate in the Electrical & Computer Engineering Department at UCLA. He is pursuing his Ph.D. at UCLA since fall 2015. He received the B.S. (summa cum laude) and M.S. degrees in electrical engineering from UCLA in 2013 and 2015, respectively. He has interned at Silicon Labs in 2013, Mediatek in 2016, Qualcomm in 2017, and Broadcom in 2019. His research interests include radio frequency and analog integrated circuit design.

For more information, contact Prof. Asad A. Abidi (abidi@ee.ucla.edu)

Date/Time:
Date(s) - Oct 16, 2020
12:00 pm - 2:00 pm

Location:
Via Zoom Only
No location, Los Angeles
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