A Digital RF Transmitter with Background Nonlinearity Correction

Speaker: S. Mehrdad Babamir
Affiliation: UCLA Ph.D. Candidate

Abstract:  Digital RF Transmitters (TXs) have gained popularity in recent years for their many advantages. They dispense with analog functions, such as baseband filters, variable gain amplifiers, and predrivers, while allowing correction of I/Q mismatches and carrier leakage in the digital domain. Moreover, they avoid the linearity-gain trade-off present in every stage of an analog TX.

The greatest challenge facing RF transmitter, analog or digital, is the trade-off between the linearity and power efficiency in the front end, specially, in the output DAC in a digital design. This issue has led to many linearization techniques. Since the die temperature varies considerably with the output power, the nonlinearity correction must continue in real time, a point addressed by no digital TX work reported to date.

In this presentation, we describe a new TX architecture that automatically corrects static and dynamic nonlinearity with no need for digital Predistortion or adaptation. We begin with the Newton-Raphson method of solving equations and show that it leads to ΔΣ modulation as a special case and to a compact, efficient digital TX in the general case. Owing to a multitude of simplifications, the TX reduces to two shift registers, four Δ modulators, and a single output DAC. To demonstrate the efficacy of the proposed concepts, a prototype has been developed for the WCDMA standard in 28-nm CMOS technology. The complete TX achieves an overall efficiency of 50% while delivering +24 dBm with an adjacent channel power of -35.4 dB and a receive-band noise of -137 dBc/Hz.

Biography:  S. Mehrdad Babamir received his B.Sc. and M.Sc. degree in Electrical Engineering from Sharif University of Technology, Tehran, Iran in 2013 and 2015.  He was a research intern in Algo Lab, EPFL University, Switzerland in 2012. He joined CCL Lab in 2015 as a Ph.D. student.  Mehrdad is also a recipient of Broadcom Fellowship in 2017.  His research interests lie in RF circuit design.

For more information, contact Prof. Behzad Razavi ()

Date(s) - May 30, 2019
2:00 pm - 4:00 pm

E-IV Maxwell Room #57-124
420 Westwood Plaza - 5th Flr. , Los Angeles CA 90095