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It is, then, a challenging exercise in analogue electronics design and manufacturing to produce a MEMS interface IC which optimises the performance of the sensor it is paired with.These characteristics, as much as the quality of the sensor itself, determine the quality of the sensor input to the system processor or microcontroller.input impedance o A clean, stable 5-20V low-noise bias voltage independent of the external supply to the IC The performance of the microphone module is strongly affected by the supply and amplification characteristics of the ams interface IC. The module offers a very low figure for total harmonic distortion (below 0.5% at 100dBSPL (Sound Pressure Level) and below 5% at 115dBSPL) and a signalto-noise ratio of 62dB(A) at 94dBSPL.ams' IC uses a Flipped Voltage Follower technique, however, to implement a capacitor-less, multiple-output LDO which offers low power consumption, provides a precisely regulated charge pump supply and occupies a small area on the die.CMOS is normally used for manufacturing digital circuits, but at ams' fab in Graz, Austria the proprietary 0.35um HV CMOS process has been optimised for high-performance analogue, while preserving the low-cost advantages that CMOS confers.Together, the combination of circuit design and manufacturing process produce an IC that interfaces directly to both the MEMS microphone and a baseband processor, with no external components required, and is capable of providing: o <5uV noise in the analogue circuit o a low 130uA current draw o <100fF input capacitance o ~10T?This specific example of the MEMS microphone module is representative of the situation facing all MEMS sensor specifiers: a combination of low noise, high voltage, high impedance and low capacitance are required to optimise the performance of the sensor, and this is produced through advanced circuit design implemented in an optimised fabrication process.

It is, then, a challenging exercise in analogue electronics design and manufacturing to produce a MEMS interface IC which optimises the performance of the sensor it is paired with. The scale of the challenge is best illustrated by reference to a real-world example of a MEMS sensor: MEMS microphones are today widely used in mobile phones and other end products, because they offer performance, stability and reliability advantages over traditional electret condenser microphones.
A MEMS microphone is a typical instance of a MEMS sensor in its electrical characteristics. In the tight physical confines of a mobile phone, it is essential that the interface integrates all the required functions, with no external components used.
Successful implementation of such a device requires a combination of advanced analogue circuit design techniques and a fabrication process optimised for low noise and high voltage. In an interface IC designed and manufactured by ams AG to partner a MEMS microphone transducer, innovative designs have achieved extremely low levels of noise in the power supply and the signal amplifier.
For instance, voltage regulation is provided with a Low Drop-Out regulator (LDO), a device type which provides good decoupling of supply and digital noise from the small-signal analogue circuit, and which produces a precise input voltage for the charge pump. But the power efficiency of conventional LDO designs is poor, an external capacitor on each output is typically required for good stability, and charge pump ripple introduces excessive noise into the sensor supply.
ams’ IC uses a Flipped Voltage Follower technique, however, to implement a capacitor-less, multiple-output LDO which offers low power consumption, provides a precisely regulated charge pump supply and occupies a small area on the die.
Innovation is also apparent in a patented* low-noise amplifier design, which again requires no external capacitor, occupies a small die area and includes low- and high-frequency noise filters.
Alongside the circuit design, ams’ HV (High Voltage) CMOS fabrication process also supports low noise and up to 120V analogue circuit operation. CMOS is normally used for manufacturing digital circuits, but at ams’ fab in Graz, Austria the proprietary 0.35µm HV CMOS process has been optimised for high-performance analogue, while preserving the low-cost advantages that CMOS confers.
Together, the combination of circuit design and manufacturing process produce an IC that interfaces directly to both the MEMS microphone and a baseband processor, with no external components required, and is capable of providing:
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