John M. Khoury

A Low-EMI 3-W Audio Class-D Amplifier Compatible With AM/FM Radio

A 3-W audio class-D amplifier compatible with AM/FM radio while requiring minimal external filtering is presented. The amplifier uses driver slew rate control to reduce electromagnetic interference (EMI) in the FM band and digital modulation to spread the PWM common-mode signal and place a null at the tuned AM channel. Two original feedback techniques are employed to linearize the H-bridge. One cancels signal-dependent propagation delays in the H-bridge to improve harmonic distortion and eliminate high-frequency noise folding into the audio band. The second technique boosts the power supply rejection ratio to simplify and reduce the cost of supply filters. The amplifier system, implemented in a standard 110-nm CMOS process, operates with a supply voltage ranging from 2.7 to 6.6 V and achieves an SNR of 95 dB and 85% efficiency.

Linearization of class D amplifiers

Signal dependent propagation delay and supply modulation are among the major sources of performance deterioration in class D amplifiers. More so in the case where the control of the common-mode EMI of a Class D amplifier utilizes DSP-based signal spreading techniques and requires the switching amplifier to be “linear” to avoid folding the high frequency spectrum into the audio band. This paper reviews the sources of nonlinearity and describes two original solutions based on analog feedback techniques for a 3W audio amplifier that were implemented in a 110 nm CMOS process.

Yannis Tsividis' Early Contributions to MOS Filters

In the 1970s, when the bipolar transistor was the undisputed king of analog integrated circuits (ICs), most electrical engineers regarded the MOS transistor as a second-rate device for ICs: it was a good switch, but a mediocre amplifier. As a graduate student at UC Berkeley, under the supervision of Paul Gray, Yannis Tsividis had a very different vision. He saw the MOS transistor as the future star for mixed-signal ICs and was excited to prove to the world he was right. The opening gambit was his thesis work demonstrating the first fully-integrated MOS opamp. This single achievement propelled him to the top of his generation of researchers and earned him a Berkeley PhD degree, a teaching appointment at Columbia University and a consulting position at Bell Laboratories.

EP2: You're hired! The top 25 interview questions for circuit designers

Circuit designers have to survive one or many technical interviews before being hired for their dream job. Many students and practicing engineers feel confident that they have a strong and intuitive understanding of circuits. However, even the best circuit designers can be stumped by exotic circuits or through a misunderstanding of fundamental concepts. This panel of industry and academic circuit designers will entertain and challenge the audience and each other with questions that often arise during job interviews. The audience can judge which interview questions are fair game in the pursuit of the highly coveted mixed-signal integrated circuit job.