Gino Rocca

A compact CMOS MEMS microphone with 66dB SNR

Silicon MEMS microphones that offer small size, ease of integration with CMOS electronics, and the ability to withstand lead-free solder reflow cycles, are becoming increasingly popular for high-volume consumer electronic products, and are competing in price and performance with traditional electret condenser microphones [1]. The design of a MEMS microphone, consisting of a compliant membrane and a stiff back-plate forming a variable capacitor, is a challenging task with a number of design trade-offs [2]. For cost reasons, a small-area membrane is desired; however, lower acoustical noise is obtained with a larger membrane. In this work, we demonstrate a method to increase the SNR of a microphone system without the need for a complicated and risky MEMS die redesign. An SNR of 66dB is achieved using two microphones (instead of a single one) in a differential configuration, thus doubling the total membrane area.

Re-configurable Switched Capacitor Sigma-Delta Modulator for MEMS Microphones in Mobiles

This paper presents a reconfigurable discrete-time audio Sigma-Delta modulator implemented in 0.18-µm CMOS technology. The 600 µm × 400 µm core area SD modulator is based on a 2 + 2 MASH architecture, and features several different operating modes in which noise-shaping order, number of output word bits, sampling rate, and bandwidth can be programmed ad hoc. By design, the power consumption is minimized for the selected operating mode. The achieved performance ranges from 99-dB DR with 4th-order noise shaping and full standard audio bandwidth, while consuming 0.97 mW down to 85-dB DR with second order noise shaping over reduced bandwidth for vocal control operation, while consuming 100 µW. The developed device can be used either to read-out different sources (microphones) or to operate in different modes within the same system (i.e. with the same microphone in different scenarios). The trade-off between performance and re-configurability is the key element of this work.

Fully integrated triple-mode sigma-delta modulator for speech codec

Mixed-signal speech processing system has been used in microphone-embedded portable electronics. Speech codec is the core of such a system. In speech codecs, sigma-delta modulator is one key block which converts analog voice signal into pulse density modulation (PDM) output for further digital signal processing. This paper shows the design of a triple-mode switched-capacitor sigma-delta modulator for speech codec. High mode (20 kHz signal bandwidth), low mode (4 kHz signal bandwidth), and sleep mode are implemented by addressing a flexible operation current. In order to realize a fully integrated solution, power management circuits dedicated to the modulator are also implemented, which includes frequency detector, LDO, bandgap and reference voltage buffers. The ASIC is fabricated in a 0.18-um CMOS process. In high mode measurement, an A-weighted signal-to-noise ratio (SNR) of 78 dB with −2.5 dBFS input is achieved under 138 uA. In low mode measurement, an SNR of 78 dB with −2 dBFS is achieved under 100 uA. In the standby condition, a sleep mode with current less than 10 uA is realized, so that the battery life is extended.

A multi-mode SC audio ΣΔ Modulator for MEMS microphones with reconfigurable power consumption, noise-shaping order, and DR

This paper presents a reconfigurable SC audio ΣΔ modulator implemented in a 0.18-mm CMOS technology. The 0.4-mm2 ΣΔ modulator, based on a 2-2 MASH architecture, features several different operating modes in which noise-shaping order, number of output bits, sampling rate, and signal bandwidth can be programmed. The power consumption is always minimized for the selected operating mode. The achieved performances range from 99-dB DR with 4th-order noise shaping over a 20-kHz bandwidth, while consuming 0.97 mW to 85-dB DR with 2nd-order noise shaping over a 4-kHz bandwidth, while consuming 100 μW. Thanks to its reconfigurability, the proposed device can be used either to read-out different sources (microphones) or to operate in different modes within the same system (i. e. with the same microphone in different scenarios). Compared to single-mode devices, such a reconfigurable ΣΔ modulator trades off slightly lower performance with higher system-level efficiency when different operating modes are required concurrently.